As filed with the Securities and Exchange Commission on March 26, 2013

Registration No. 333-187145

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

 

Amendment No. 1
To
FORM S-1
  
REGISTRATION STATEMENT
UNDER THE SECURITIES ACT OF 1933

 

Chimerix, Inc.

(Exact Name of Registrant as Specified in Its Charter)

Delaware		2834		33-0903395
(State or Other Jurisdiction of Incorporation or Organization)		(Primary Standard Industrial Classification Code Number)		(I.R.S. Employer Identification Number)

2505 Meridian Parkway, Suite 340
Durham, NC 27713
(919) 806-1074

(Address, Including Zip Code, and Telephone Number,
Including Area Code, of Registrant’s Principal Executive Offices)

 

Kenneth I. Moch
President and Chief Executive Officer
Chimerix, Inc.
2505 Meridian Parkway, Suite 340
Durham, NC 27713
(919) 806-1074

(Name, Address, Including Zip Code, and Telephone Number,
Including Area Code, of Agent for Service)

 

Copies to:

Jason L. Kent, Esq. Cooley LLP 4401 Eastgate Mall San Diego, CA 92121 (858) 550-6000		Timothy W. Trost Senior Vice President, Chief Financial Officer and Corporate Secretary Chimerix, Inc. 2505 Meridian Parkway, Suite 340 Durham, NC 27713 (919) 806-1074		Richard D. Truesdell, Jr., Esq. Davis Polk & Wardwell LLP 450 Lexington Avenue New York, NY 10017 (212) 450-4000

 

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended (the “Securities Act”), check the following box. o

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer o		Accelerated filer o
Non-accelerated filer x (Do not check if a smaller reporting company)		Smaller reporting company o

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CALCULATION OF REGISTRATION FEE

Title of each class of securities to be registered		Proposed maximum aggregate offering price(1)				Amount of registration fee(2)
Common Stock, $0.001 par value per share		$	85,000,000			$	11,594

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment that specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

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The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and we are not soliciting offers to buy these securities in any state where the offer or sale is not permitted.

PROSPECTUS (Subject to Completion)
Issued            , 2013

         Shares

COMMON STOCK

 

Chimerix, Inc. is offering         shares of its common stock. This is our initial public offering and no public market currently exists for our shares. We anticipate that the initial public offering price of our common stock will be between $         and $         per share.

 

We have applied to list our common stock on the Nasdaq Global Market under the symbol CMRX.

We are an emerging growth company as that term is used in the Jumpstart Our Business Startups Act of 2012 and, as such, have elected to comply with certain reduced public company reporting requirements for this prospectus and future filings.

 

Investing in our common stock involves risks. See “Risk Factors” beginning on page 10.

 

PRICE $       A SHARE

 

Price to Public

Underwriting Discounts and Commissions

Proceeds to Company(1)

Per Share

$

$

$

Total

$

$

$

Chimerix, Inc. has granted the underwriters the right to purchase up to an additional          shares of common stock to cover over-allotments.

Entities affiliated with certain of our existing stockholders and directors have indicated an interest in purchasing up to an aggregate of approximately $     million in shares of our common stock in this offering at the initial public offering price. However, because indications of interest are not binding agreements or commitments to purchase, the underwriters could determine to sell more, less or no shares to any of these potential investors and any of these potential investors could determine to purchase more, less or no shares in this offering.

The Securities and Exchange Commission and state securities regulators have not approved or disapproved these securities, or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares of common stock to purchasers on            , 2013.

 

MORGAN STANLEY		COWEN AND COMPANY

 

WILLIAM BLAIR		LAZARD CAPITAL MARKETS

           , 2013

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		Page
Prospectus Summary			1
Risk Factors			10
Special Note Regarding Forward-Looking Statements			39
Market, Industry and Other Data			40
Use of Proceeds			41
Dividend Policy			42
Capitalization			43
Dilution			45
Selected Financial Data			48
Management’s Discussion and Analysis of Financial Condition and Results of Operations			50
Business			71
Management			113

		Page
Executive and Director Compensation			121
Certain Relationships and Related Party Transactions			139
Principal Stockholders			143
Description of Capital Stock			146
Shares Eligible for Future Sale			152
Material U.S. Federal Income Tax Consequences to Non-U.S. Holders of our Common Stock			154
Underwriters			157
Legal Matters			162
Experts			162
Where You Can Find Additional Information			162
Index to Financial Statements			F-1

  

 

Neither we nor any of the underwriters has authorized anyone to provide you with information different from, or in addition to, that contained in this prospectus or any free writing prospectus prepared by or on behalf of us or to which we may have referred you in connection with this offering. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. Neither we nor any of the underwriters is making an offer to sell or seeking offers to buy these securities in any jurisdiction where or to any person to whom the offer or sale is not permitted. The information in this prospectus is accurate only as of the date on the front cover of this prospectus and the information in any free writing prospectus that we may provide you in connection with this offering is accurate only as of the date of that free writing prospectus. Our business, financial condition, results of operations and future growth prospects may have changed since those dates.

Through and including            , 2013 (25 days after the commencement of this offering), all dealers that effect transactions in these securities, whether or not participating in this offering, may be required to deliver a prospectus. This delivery is in addition to a dealer’s obligation to deliver a prospectus when acting as an underwriter and with respect to their unsold allotments or subscriptions.

This prospectus includes statistical and other industry and market data that we obtained from industry publications and research, surveys and studies conducted by third parties. Industry publications and third-party research, surveys and studies generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information. While we believe these industry publications and third-party research, surveys and studies are reliable, we have not independently verified such data.

For investors outside the United States: neither we nor any of the underwriters has done anything that would permit this offering or possession or distribution of this prospectus or any free writing prospectus we may provide to you in connection with this offering in any jurisdiction where action for that purpose is required, other than in the United States. You are required to inform yourselves about and to observe any restrictions relating to this offering and the distribution of this prospectus and any such free writing prospectus outside of the United States.

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PROSPECTUS SUMMARY

This summary highlights information contained in other parts of this prospectus. Because it is only a summary, it does not contain all of the information that you should consider before investing in shares of our common stock and it is qualified in its entirety by, and should be read in conjunction with, the more detailed information appearing elsewhere in this prospectus. You should read the entire prospectus carefully, especially “Risk Factors” and our financial statements and the related notes, before deciding to buy shares of our common stock. Unless the context requires otherwise, references in this prospectus to “Chimerix”, the “Company”, “we”, “us” and “our” refer to Chimerix, Inc.

Overview

Chimerix is a biopharmaceutical company committed to the discovery, development and commercialization of novel, oral antiviral therapeutics that are designed to transform patient care in areas of high unmet medical need. Our proprietary lipid technology has given rise to two clinical-stage compounds, CMX001 and CMX157, which have demonstrated the potential for enhanced antiviral activity and safety in convenient, orally administered dosing regimens. We have worldwide rights to our lead product candidate, CMX001, and anticipate beginning the Phase 3 SUPPRESS study in 2013 for the prevention of cytomegalovirus (CMV) infection in hematopoietic stem cell transplant (HSCT) recipients. We intend to develop CMX001 as the first broad-spectrum antiviral against double-stranded DNA (dsDNA) viruses. Our second clinical-stage compound, CMX157, is a Phase 1 product candidate for the treatment of HIV and was licensed to Merck, Sharp & Dohme Corp. (Merck) in 2012.

CMX001 is an orally administered drug that utilizes our proprietary lipid technology to deliver high intracellular concentrations of a potent antiviral compound, cidofovir-diphosphate (CDV-PP). Following oral dosing, CMX001 is absorbed through the gut, remains intact in the plasma, and is readily taken up by and delivered into cells. Once inside cells, CMX001 is converted into CDV-PP, which acts as an alternative substrate that interferes with the enzymes necessary for viral replication. When CDV-PP is selected by critical enzymes as a substrate over the normal cellular substrate (i.e. nucleotides), the result is diminished enzymatic activity and therefore diminished viral replication.

CMX001 is similar to the drug cidofovir in that both drugs are converted into CDV-PP once inside cells. Although cidofovir is approved for administration in an intravenous formulation, Vistide, it requires a high plasma concentration to deliver a therapeutic level of cidofovir into cells and its use is limited due to the risk of kidney damage. In contrast, oral administration of CMX001 results in significantly lower plasma concentrations, higher levels of drug inside cells, and a lower risk of kidney toxicity.

Double-stranded DNA viral infections such as CMV are commonly transmitted in childhood and early adulthood, and generally remain latent in individuals with a functioning immune system. However, in immunocompromised patients, such as HSCT or solid organ transplant (SOT) recipients, CMV and other dsDNA viral infections are associated with significant morbidity, mortality, graft rejection and co-infection with other opportunistic infections. CMV, a human herpesvirus, is the most common infectious pathogen in HSCT, and can result in life-threatening pneumonia or other organ involvement, particularly in the first 100 days following transplant when the immune system is most vulnerable. In vitro, CMX001 has shown broad-spectrum antiviral activity against all families of dsDNA viruses that cause human disease, including herpesviruses, adenoviruses (AdV), polyomaviruses such as BK virus (BKV), papillomaviruses and orthopoxviruses.

In the HSCT setting, there are three paradigms for addressing viral infections: prevention, preemptive therapy and treatment of disease. Prevention is the administration of an antiviral to at-risk patients to avoid reactivation of a latent virus. Preemptive therapy is the initiation of antiviral(s) only after detection of a specific virus in the blood (viremia) in an asymptomatic patient. Treatment is the watch-and-wait approach of initiating antiviral therapy after the virus is detected in an organ system where clinical signs or symptoms are present.

No drugs are approved for prevention of CMV in HSCT recipients, primarily due to significant renal and hematological side effects. We believe that a safe and well-tolerated antiviral with demonstrated efficacy in prevention settings would provide a new standard of care for immunocompromised patients. In HSCT, a safe

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and effective therapy for CMV prevention could potentially replace the current practice of frequent monitoring for CMV viremia and initiation of anti-CMV preemptive therapy following detection. In addition, we believe that an antiviral that could reduce the frequency of other dsDNA viruses and avoid increasing the risk of other opportunistic infections could provide measureable clinical and pharmacoeconomic benefits for patients and the health care system.

Chimerix demonstrated the potential of CMX001 in a 230-patient Phase 2 dose-escalation study for the prevention of CMV reactivation in HSCT recipients. In this study, CMX001 or placebo was administered to HSCT recipients from stem cell engraftment through Week 13 post-transplant. A reduction of more than 50% in risk of CMV infection was observed for the subjects who received CMX001 in 100 mg doses twice weekly (BIW). Ten percent of subjects (five of 50 subjects) in the CMX001 100 mg BIW cohort met the primary endpoint, CMV disease or a positive quantitative blood test for CMV at the end of the dosing period, versus 37% of subjects (22 of 59 subjects) in the placebo cohort (p=0.002, where the p-value is the statistical probability of a result not due to chance alone). CMX001’s dose-limiting toxicity was diarrhea, which was addressed with a Safety Monitoring and Management Plan (SMMP) incorporated in the final Phase 2 cohort and in subsequent studies, and which will be implemented in SUPPRESS. There was no evidence of kidney, hematologic or bone marrow toxicity in this study.

The results of this Phase 2 study, together with CMX001’s overall preclinical and clinical profile, which includes a safety database of more than 800 subjects exposed to CMX001 in controlled and uncontrolled clinical studies, support the progression to a Phase 3 study of CMX001 for the prevention of CMV infection in high-risk HSCT recipients. Discussions with the FDA have resulted in an agreed population, endpoint and study design for which we have received a “Study May Proceed” letter. We remain in active discussions with the FDA regarding final protocol specifics and anticipate initiation of dosing in 2013. The primary endpoint is a composite endpoint of either (i) CMV disease, or (ii) initiation of anti-CMV preemptive therapy triggered by a positive test for CMV in the blood (viremia), and will be assessed through Week 24 post-transplant. We intend to enroll 540 at-risk (i.e., with latent CMV infection) HSCT recipients who will be randomized to receive one of two twice-weekly doses of CMX001 or placebo. Secondary endpoints include pharmacoeconomic data and the incidence of disease and reactivation of other herpesviruses, AdV, and BKV.

We intend to submit a new drug application (NDA) under an accelerated approval pathway seeking regulatory approval to market CMX001 in the United States and equivalent applications outside the United States. We have received Fast Track designation from the FDA for the CMV, AdV and smallpox indications for CMX001.

We believe that there is a significant commercial opportunity for an antiviral such as CMX001 with broad-spectrum activity against dsDNA viruses. According to the Center for International Blood and Marrow Transplant Research and the Organ Procurement and Transplantation Network, more than 20,000 HSCTs and 28,000 SOTs are performed annually in the United States, with similar numbers of transplants performed annually in Europe according to the European Group for Blood and Marrow Transplantation and the World Health Organization. More than 65% of stem cell transplant patients are at increased risk of CMV infection due to prior exposure to CMV (i.e., seropositive). Outside the transplant population, many factors are influencing the epidemiology of dsDNA viral infections, including the use of potent immunosuppressive therapies in autoimmune and other diseases. Since 2009, Chimerix has made CMX001 available under expanded access regulations to over 80 transplant centers worldwide for the treatment of over 430 patients with life-threatening dsDNA viral infections and no satisfactory alternative treatment options, reflecting the unmet medical need in this therapeutic area. Our CMX001 Compassionate Use Program consists of the emergency investigational new drug (EIND) program which has provided treatment to 230 individuals and Study 350, the expanded access study which enrolled 215 patients meeting similar inclusion criteria as the EINDs.

If CMX001 obtains regulatory approval, we intend to build our own sales force and to commercialize CMX001. In the United States, approximately 200 institutions perform transplants, of which approximately 75% perform HSCT and 75% perform SOT. As a result, we believe we can commercialize CMX001 for prevention of CMV in HSCT recipients in the United States and Canada with a relatively small marketing and specialty sales force infrastructure of approximately 50 employees.

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We are also evaluating the potential for CMX001 as a preemptive therapy for AdV infections. In December 2012, we completed enrollment of a Phase 2 placebo-controlled study of preemptive therapy for AdV viremia in 48 pediatric and adult HSCT recipients. Data on the mortality and disease endpoints for this Phase 2 study are expected during the second half of 2013. Future clinical development for CMX001 may include a Phase 3 CMV prevention study in pediatric HSCT recipients, as well as the possible development of CMX001 for BKV infection in HSCT and SOT recipients.

CMX157, our second clinical stage compound, is an oral nucleotide compound in Phase 1 development for the treatment of HIV infection. In July 2012, we granted Merck an exclusive worldwide license to develop and commercialize CMX157 for all human uses. Merck is responsible for all development and marketing activities for CMX157 on a worldwide basis.

Our Strategy

Our strategy is to discover, develop, and commercialize novel oral antiviral therapeutics in areas of significant unmet medical need. Key elements of our strategy include:

We may enter into additional collaborations to implement our strategy.

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Our Product Candidates

The following chart depicts our product candidates, their indications, and their current stage of development:

Risks Associated with Our Business

Our business is subject to numerous risks, as more fully described in the section entitled “Risk Factors” immediately following this prospectus summary. You should read these risks before you invest in our common stock. We may be unable, for many reasons, including those that are beyond our control, to implement our business strategy. In particular, risks associated with our business include:

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Corporate Information

We were incorporated in Delaware in April 2000. Our principal executive offices are located at 2505 Meridian Parkway, Suite 340, Durham, North Carolina 27713, and our telephone number is (919) 806-1074. Our corporate website address is www.chimerix.com. Information contained on or accessible through our website is not a part of this prospectus, and the inclusion of our website address in this prospectus is an inactive textual reference only.

We have obtained a registered trademark for Chimerix® in the United States. This prospectus contains references to our trademarks and to trademarks belonging to other entities. Solely for convenience, trademarks and trade names referred to in this prospectus, including logos, artwork and other visual displays, may appear without the ® or ^TM symbols, but such references are not intended to indicate, in any way, that we will not assert, to the fullest extent under applicable law, our rights or the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other companies’ trade names or trademarks to imply a relationship with, or endorsement or sponsorship of us by, any other companies.

We are an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012. We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of this offering, (b) in which we have total annual gross revenue of at least $1.0 billion, or (c) in which we are deemed to be a large accelerated filer, which means the market value of our common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30th, and (2) the date on which we have issued more than $1.0 billion in non-convertible debt during the prior three-year period. We refer to the Jumpstart Our Business Startups Act of 2012 in this prospectus as the “JOBS Act,” and references in this prospectus to “emerging growth company” shall have the meaning associated with it in the JOBS Act.

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THE OFFERING

Entities affiliated with certain of our existing stockholders and directors have indicated an interest in purchasing up to an aggregate of approximately $     million in shares of our common stock in this offering at the initial public offering price. However, because indications of interest are not binding agreements or commitments to purchase, the underwriters could determine to sell more, less or no shares to any of these potential investors and any of these potential investors could determine to purchase more, less or no shares in this offering. Any shares purchased by our existing stockholders and directors will be subject to lock-up restrictions described in “Shares Eligible for Future Sale.”

The number of shares of our common stock to be outstanding after this offering is based on 16,014,083 shares of common stock outstanding as of December 31, 2012, and excludes:

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Unless otherwise indicated, all information contained in this prospectus assumes:

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SUMMARY FINANCIAL DATA

The following summary financial data should be read together with our financial statements and related notes, “Selected Financial Data” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” appearing elsewhere in this prospectus. Our historical results are not necessarily indicative of the results that may be expected in the future and results of interim periods are not necessarily indicative of the results for the entire year.

We derived the following summary statement of operations data for the years ended December 31, 2010, 2011 and 2012 from our audited financial statements and related notes appearing elsewhere in this prospectus.

		Year Ended December 31,
Statement of Operations Data:		2010				2011				2012
		(in thousands, except share and per share data)
Revenues:
Collaboration and licensing revenues		$	—			$	55			$	17,445
Contract and grant revenues			1,715				12,046				16,275
Total revenues			1,715				12,101				33,720
Operating expenses:
Research and development			19,413				27,695				27,821
General and administrative			7,606				9,398				8,682
Total operating expenses			27,019				37,093				36,503
Loss from operations			(25,304	)			(24,992	)			(2,783	)
Interest income (expense), net			(154	)			(212	)			(776	)
Fair value adjustment to warrant liability			—				(385	)			(847	)
Other income			1				—				—
Net loss			(25,457	)			(25,589	)			(4,406	)
Accretion of redeemable convertible preferred stock			—				(9,565	)			(4,357	)
Net loss attributable to common stockholders		$	(25,457	)		$	(35,154	)		$	(8,763	)
Basic and diluted net loss per common share(1)		$	(17.52	)		$	(23.49	)		$	(5.75	)
Shares used to calculate net loss per common share(1)			1,453				1,496				1,525
Pro forma net loss per common share, basic and diluted (unaudited)(2)
Shares used to calculate pro forma net loss per common share, basic and diluted (unaudited)(2)

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		As of December 31, 2012
		Actual				Pro Forma(3)				Pro Forma as Adjusted(4)(5)
						(unaudited)
						(in thousands)
Balance Sheet Data:
Cash and cash equivalents		$	19,906			$	19,906			$
Short-term investments, available-for-sale			9,849				9,849
Working capital			23,931				23,931
Total assets			32,031				32,031
Loan payable(6)			14,620				14,620
Redeemable convertible preferred stock warrant liability			7,512				—
Redeemable convertible preferred stock			107,723				—
Total stockholders’ equity (deficit)			(101,031	)			14,204

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RISK FACTORS

An investment in shares of our common stock involves a high degree of risk. You should carefully consider the following information about these risks, together with the other information appearing elsewhere in this prospectus, before deciding to invest in our common stock. The occurrence of any of the following risks could have a material adverse effect on our business, financial condition, results of operations and future growth prospects. In these circumstances, the market price of our common stock could decline, and you may lose all or part of your investment.

Risks Related to Our Financial Condition and Need for Additional Capital

We have incurred significant losses since our inception. We anticipate that we will continue to incur significant losses for the foreseeable future, and we may never achieve or maintain profitability.

We are a biopharmaceutical company focused primarily on developing our lead product candidate, CMX001. We have incurred significant net losses in each year since our inception, including net losses of approximately $25.5 million, $25.6 million and $4.4 million for the fiscal years ended 2010, 2011 and 2012, respectively. As of December 31, 2012, we had an accumulated deficit of $101.0 million.

To date, we have financed our operations primarily through the sale of equity securities and, to a lesser extent, through government funding, licensing fees and debt. We have devoted most of our financial resources to research and development, including our preclinical development activities and clinical trials. We have not completed development of any product candidates. We expect to continue to incur significant and increasing losses and negative cash flows for the foreseeable future. The size of our losses will depend, in part, on the rate of future expenditures and our ability to generate revenues. In particular, we expect to incur substantial and increased expenses as we:

To become and remain profitable, we must succeed in developing and eventually commercializing products with significant market potential. This will require us to be successful in a range of challenging activities, including discovering product candidates, completing preclinical testing and clinical trials of our product candidates, obtaining regulatory approval for these product candidates, and manufacturing, marketing and selling those products for which we may obtain regulatory approval. We are only in the preliminary stages of some of these activities.

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To date, we have not completed Phase 3 clinical trials or obtained regulatory approval for any of our product candidates, and none of our product candidates have been commercialized. We may never succeed in developing or commercializing any of our product candidates. If our product candidates are not successfully developed or commercialized, or if revenues from any products that do receive regulatory approvals are insufficient, we will not achieve profitability and our business may fail. Even if we successfully obtain regulatory approval to market our product candidates in the United States, our revenues are also dependent upon the size of markets outside of the United States, as well as our ability to obtain market approval and achieve commercial success outside of the United States.

Even if we do achieve profitability, we may not be able to sustain or increase profitability on a quarterly or annual basis. Our failure to become and remain profitable would depress the value of our company and could impair our ability to raise capital, expand our business, diversify our product offerings or continue our operations. A decline in the value of our company could cause you to lose all or part of your investment.

Our ability to generate future revenues from product sales is uncertain and depends upon our ability to successfully develop, obtain regulatory approval for, and commercialize our product candidates.

Our ability to generate revenue and achieve profitability depends on our ability, alone or with collaborators, to successfully complete the development, obtain the necessary regulatory approvals and commercialize our product candidates. We do not anticipate generating revenues from sales of our product candidates for the foreseeable future, if ever. Our ability to generate future revenues from product sales depends heavily on our success in:

Conducting preclinical testing and clinical trials is a time-consuming, expensive and uncertain process that takes years to complete, and we may never generate the necessary data required to obtain regulatory approval and achieve product sales. Our anticipated development costs would likely increase if we do not obtain favorable results or if development of our product candidates is delayed. In particular, we would likely incur higher costs than we currently anticipate if development of our product candidates is delayed because we are required by the United States Food and Drug Administration (FDA) to perform studies or trials in addition to those that we currently anticipate. Because of the numerous risks and uncertainties associated with pharmaceutical product development, we are unable to predict the timing or amount of any increase in our anticipated development costs.

In addition, our product candidates, if approved, may not achieve commercial success. Our commercial revenues, if any, will be derived from sales of products that we do not expect to be commercially available for several years, if at all. Even if one or more of our product candidates is approved for commercial sale, we anticipate incurring significant costs in connection with commercialization. As a result, we cannot assure you that we will be able to generate revenues from sales of any approved product candidates, or that we will achieve or maintain profitability even if we do generate sales.

If we fail to obtain additional financing, we could be forced to delay, reduce or eliminate our product development programs, seek corporate partners for the development of our product development programs or relinquish or license on unfavorable terms, our rights to technologies or product candidates.

Developing pharmaceutical products, including conducting preclinical studies and clinical trials, is a time-consuming, expensive and uncertain process that takes years to complete. We expect our research and

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development expenses to substantially increase in connection with our ongoing activities, particularly as we advance our clinical programs for CMX001.

We estimate that the net proceeds from this offering will be approximately $     million, assuming an initial public offering price of $     per share (the mid-point of the price range set forth on the cover page of this prospectus) after deducting estimated underwriting discounts and commissions and offering expenses payable by us. Based upon our current operating plan, we believe that the net proceeds from this offering, together with our existing cash, cash equivalents and short-term investments, will enable us to fund our operating expenses and capital requirements at least through mid-2015. However, changing circumstances beyond our control may cause us to consume capital more rapidly than we currently anticipate. For example, our clinical trials may encounter technical, enrollment or other difficulties that could increase our development costs more than we expected, or because the FDA requires us to perform studies or trials in addition to those that we currently anticipate. We may need to raise additional funds if we choose to initiate clinical trials for our product candidates other than CMX001. In any event, we will require additional capital to obtain regulatory approval for, and to commercialize, our product candidates.

Securing additional financing may divert our management from our day-to-day activities, which may adversely affect our ability to develop and commercialize our product candidates, including CMX001. In addition, we cannot guarantee that future financing will be available in sufficient amounts or on terms acceptable to us, if at all. If we are unable to raise additional capital when required or on acceptable terms, we may be required to:

If we are unable to raise additional capital in sufficient amounts or on terms acceptable to us, we will be prevented from pursuing development and commercialization efforts, which will have a material adverse effect on our business, operating results and prospects and on our ability to develop our product candidates.

Raising additional capital may cause dilution to our existing stockholders, restrict our operations or require us to relinquish rights to our technologies or product candidates.

Until such time, if ever, as we can generate substantial product revenues, we expect to finance our cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other marketing and distribution arrangements. We do not have any committed external source of funds. Under our collaboration and license agreement with Merck, we are entitled to receive milestone and royalty payments if specified events occur, but that agreement is terminable by Merck at any time upon 90 days written notice or, in certain circumstances, immediately upon written notice.

In order to raise additional funds to support our operations, we may sell additional equity or debt securities, enter into collaborations, strategic alliances, or licensing arrangements or other marketing or distribution arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, your ownership interest will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect your rights as a stockholder. Debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures, and declaring dividends, and will impose limitations on our ability to acquire, sell or license intellectual property rights and other operating restrictions that could adversely impact our ability to conduct our business.

If we raise additional funds through collaborations, strategic alliances, or licensing arrangements or other marketing or distribution arrangements with third parties, we may have to relinquish valuable rights to our technologies, future revenue streams, research programs or product candidates, or grant licenses on terms that

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may not be favorable to us. If we are unable to expand our operations or otherwise capitalize on our business opportunities, our business, financial condition and results of operations could be materially adversely affected and we may not be able to meet our debt service obligations. If we are unable to raise additional funds through equity or debt financings when needed, we may be required to delay, limit, reduce or terminate our product development or commercialization efforts, or grant others rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

We may be required to repay the outstanding indebtedness under our loan agreement if a material adverse change occurs with respect to us, which could have a materially adverse effect on our business.

As of December 31, 2012, we had $15.0 million of indebtedness outstanding under our loan and security agreement with Silicon Valley Bank (SVB) and MidCap Financial SBIC, L.P. (MidCap). Under the loan agreement, an event of default will occur if, among other things, a material adverse change in our business, operations or condition occurs, or a material impairment of the prospect of our repayment of any portion of the amounts we owe under the loan agreement occurs. An event of default would allow the lenders to, among other things, accelerate the loan and take certain action with respect to the collateral securing our obligations under the loan agreement. We may not have enough available cash or be able to raise additional funds through equity or debt financings to repay such indebtedness at the time any such event of default occurs. In this case, we may be required to delay, limit, reduce or terminate our product development or commercialization efforts or grant to others, rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves. Our business, financial condition and results of operations could be materially adversely affected as a result.

Risks Related to Clinical Development and Regulatory Approval

We depend on the success of our lead product candidate, CMX001, which is still under clinical development, and may not obtain regulatory approval or be successfully commercialized.

We have not marketed, distributed or sold any products. The success of our business depends upon our ability to develop and commercialize our lead product candidate, CMX001, which has completed a Phase 2 clinical trial for the prevention of CMV infection in HSCT patients. We plan to initiate a Phase 3 clinical trial for CMX001 for the prevention of CMV infection in adult HSCT patients. We intend to use this trial as a basis to submit a new drug application (NDA) to the FDA under the accelerated approval pathway seeking regulatory approval to market CMX001 in the United States and equivalent applications outside the United States. We also intend to conduct a separate Phase 3 clinical trial for the prevention of CMV infection in pediatric HSCT recipients. There is no guarantee that our Phase 3 clinical trials will be completed or, if completed, will be successful. The success of CMX001 will depend on several factors, including the following:

If we do not achieve one or more of these factors in a timely manner or at all, we could experience significant delays or an inability to successfully commercialize CMX001, which would materially harm our business.

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We have never obtained regulatory approval for a drug and we may be unable to obtain, or may be delayed in obtaining, regulatory approval for CMX001.

We have never obtained regulatory approval for a drug. It is possible that the FDA may refuse to accept our NDA for substantive review or may conclude after review of our data that our application is insufficient to obtain regulatory approval of CMX001. If the FDA does not accept or approve our NDA, it may require that we conduct additional clinical, nonclinical or manufacturing validation studies and submit that data before it will reconsider our application. Depending on the extent of these or any other FDA required studies, approval of any NDA or application that we submit may be delayed by several years, or may require us to expend more resources than we have available. It is also possible that additional studies, if performed and completed, may not be considered sufficient by the FDA to approve our NDA.

Any delay in obtaining, or an inability to obtain, regulatory approvals would prevent us from commercializing CMX001, generating revenues and achieving and sustaining profitability. If any of these outcomes occur, we may be forced to abandon our development efforts for CMX001, which would have a material adverse effect on our business and could potentially cause us to cease operations.

We depend on the successful completion of clinical trials for our product candidates, including CMX001. The positive clinical results obtained for our product candidates in prior clinical studies may not be repeated in future clinical studies.

Before obtaining regulatory approval for the sale of our product candidates, including CMX001, we must conduct extensive clinical trials to demonstrate the safety and efficacy of our product candidates in humans. Clinical testing is expensive, difficult to design and implement, can take many years to complete and is uncertain as to outcome. A failure of one or more of our clinical trials can occur at any stage of testing. The outcome of preclinical testing and early clinical trials may not be predictive of the success of later clinical trials, and interim results of a clinical trial do not necessarily predict final results. Moreover, preclinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that have believed their product candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failed to obtain marketing approval for their products.

We have completed a Phase 2 clinical study of CMX001 for the prevention of CMV infection in HSCT patients and have an ongoing Phase 2 study of CMX001 as preemptive therapy for AdV infection in HSCT patients. In addition, we have completed an initial Phase 1 study with CMX157. However, we have never conducted a pivotal Phase 3 clinical trial. The positive results we have seen to date in our Phase 2 clinical trial of CMX001 for the prevention of CMV in HSCT patients do not ensure that later clinical trials, such as our planned Phase 3 clinical trials, will demonstrate similar results. Product candidates in later stages of clinical trials may fail to show the desired safety and efficacy characteristics despite having progressed satisfactorily through preclinical studies and initial clinical testing. A number of companies in the pharmaceutical and biotechnology industries, including those with greater resources and experience than us, have suffered significant setbacks in Phase 3 clinical development, even after seeing promising results in earlier clinical trials.

We may experience a number of unforeseen events during, or as a result of, clinical trials for our product candidates, including CMX001, that could adversely affect the completion of our clinical trials, including:

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Negative or inconclusive results of our Phase 3 clinical trial of CMX001, which we refer to as SUPPRESS, or any other clinical trial we conduct, could cause the FDA to require that we repeat or conduct additional clinical studies. Despite the results reported in earlier clinical trials for CMX001, we do not know whether SUPPRESS or any other clinical trials we may conduct will demonstrate adequate efficacy and safety to result in regulatory approval to market our product candidates, including CMX001. If later stage clinical trials do not produce favorable results, our ability to obtain regulatory approval for our product candidates, including CMX001, may be adversely impacted.

We are developing CMX001 to treat patients who are extremely ill, and patient deaths that occur in our clinical trials could negatively impact our business even if they are not shown to be related to CMX001.

We are developing our lead product candidate, CMX001, for the prevention of CMV infection in HSCT patients and we plan on initiating SUPPRESS, which will focus on the prevention of CMV in high-risk HSCT patients. These patients receive HSCT as a potential cure or remission for many cancers and genetic disorders.

To prepare for their transplant, such patients receive a pre-transplant conditioning regimen, which involves high-dose chemotherapy and may also include radiation therapy. The conditioning regimen suppresses the patient’s immune system and/or own bone marrow in order to prevent it from attacking the newly transplanted cells. Generally, patients remain at high risk during the first 100 days following their transplant and can readily acquire infections during that period, which can be serious and even life threatening due to their weakened immune systems. As a result, it is likely that we will observe severe adverse outcomes during our Phase 3 trial for CMX001, including patient death. If a significant number of study subject deaths were to occur, regardless of whether such deaths are attributable to CMX001, our ability to obtain regulatory approval for CMX001 may be adversely impacted and our business could be materially harmed.

Delays in clinical trials are common and have many causes, and any delay could result in increased costs to us and jeopardize or delay our ability to obtain regulatory approval and commence product sales.

Clinical testing is expensive, difficult to design and implement, can take many years to complete, and is uncertain as to outcome. We may experience delays in clinical trials at any stage of development and testing of our product candidates. We plan to initiate SUPPRESS in 2013. Our planned clinical trials may not begin on time, have an effective design, enroll a sufficient number of subjects, or be completed on schedule, if at all.

Events which may result in a delay or unsuccessful completion of clinical trials, including our Phase 3 clinical trial for CMX001, include:

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For example, due to the specialized indication and patient population being studied in our Phase 3 clinical trial of CMX001, the number of study sites available to us is relatively limited, and therefore enrollment of suitable patients to participate in the trial may take longer than is typical for studies involving other indications. This may result in a delay or unsuccessful completion of our Phase 3 clinical trial of CMX001.

If initiation or completion of any of our clinical trials for our product candidates, including our Phase 3 clinical trial of CMX001, are delayed for any of the above reasons, our development costs may increase, our approval process could be delayed, any periods during which we may have the exclusive right to commercialize our product candidates may be reduced and our competitors may have more time to bring products to market before we do. Any of these events could impair our ability to generate revenues from product sales and impair our ability to generate regulatory and commercialization milestones and royalties, all of which could have a material adverse effect on our business.

Our product candidates may cause adverse effects or have other properties that could delay or prevent their regulatory approval or limit the scope of any approved label or market acceptance.

Adverse events (AEs) caused by our product candidates could cause us, other reviewing entities, clinical study sites or regulatory authorities to interrupt, delay or halt clinical studies and could result in the denial of regulatory approval. For example, subjects enrolled in our Phase 2 clinical trials for CMX001 have reported gastrointestinal and liver-related AEs and safety laboratory value changes. Furthermore, CMX001 is related to the approved drug cidofovir (CDV), a compound which has been shown to result in significant renal toxicity and impairment following use. There is also a risk that our other product candidates may induce AEs, many of which may be unknown at this time. If an unacceptable frequency and/or severity of AEs are reported in our clinical trials for our product candidates, our ability to obtain regulatory approval for product candidates, including CMX001, may be negatively impacted.

Furthermore, if any of our approved products cause serious or unexpected side effects after receiving market approval, a number of potentially significant negative consequences could result, including:

Any of these events could prevent us from achieving or maintaining market acceptance of the affected product candidate and could substantially increase the costs of commercializing our product candidates.

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After the completion of our clinical trials, we cannot predict whether or when we will obtain regulatory approval to commercialize CMX001 and we cannot, therefore, predict the timing of any future revenue from CMX001.

We cannot commercialize our product candidates, including CMX001, until the appropriate regulatory authorities, such as the FDA, have reviewed and approved the product candidate. The regulatory agencies may not complete their review processes in a timely manner, or we may not be able to obtain regulatory approval for CMX001. Additional delays may result if CMX001 is brought before an FDA advisory committee, which could recommend restrictions on approval or recommend non-approval of the product candidate. In addition, we may experience delays or rejections based upon additional government regulation from future legislation or administrative action, or changes in regulatory agency policy during the period of product development, clinical studies and the review process. As a result, we cannot predict when, if at all, we will receive any future revenue from commercialization of any of our product candidates, including CMX001.

Even if we obtain regulatory approval for CMX001 and our other product candidates, we will still face extensive regulatory requirements and our products may face future development and regulatory difficulties.

Even if we obtain regulatory approval in the United States, the FDA may still impose significant restrictions on the indicated uses or marketing of our product candidates, including CMX001, or impose ongoing requirements for potentially costly post-approval studies or post-market surveillance. For example, the labeling ultimately approved for our product candidates, including CMX001, will likely include restrictions on use due to the specific patient population and manner of use in which the drug was evaluated and the safety and efficacy data obtained in those evaluations. In addition, the label for CMX001 may be required to include a boxed warning, or “black box,” regarding CMX001 being carcinogenic, teratogenic and impairing fertility in animal studies, as well as a contraindication in patients who have had a demonstrated clinically significant hypersensitivity reaction to CMX001 or CDV or any component of the formulation. The CMX001 labeling may also include warnings or black boxes pertaining to gastrointestinal or liver-related AEs or safety laboratory value changes.

CMX001 and our other product candidates will also be subject to additional ongoing FDA requirements governing the labeling, packaging, storage, distribution, safety surveillance, advertising, promotion, record-keeping and reporting of safety and other post-market information. The holder of an approved NDA is obligated to monitor and report AEs and any failure of a product to meet the specifications in the NDA. The holder of an approved NDA must also submit new or supplemental applications and obtain FDA approval for certain changes to the approved product, product labeling or manufacturing process. Advertising and promotional materials must comply with FDA rules and are subject to FDA review, in addition to other potentially applicable federal and state laws. Furthermore, promotional materials must be approved by the FDA prior to use for any drug receiving accelerated approval, the pathway we are pursuing for CMX001 in the United States.

In addition, manufacturers of drug products and their facilities are subject to payment of user fees and continual review and periodic inspections by the FDA and other regulatory authorities for compliance with current good manufacturing practices (cGMP), and adherence to commitments made in the NDA. If we, or a regulatory agency, discover previously unknown problems with a product, such as quality issues or AEs of unanticipated severity or frequency, or problems with the facility where the product is manufactured, a regulatory agency may impose restrictions relative to that product or the manufacturing facility, including requiring recall or withdrawal of the product from the market or suspension of manufacturing.

If we fail to comply with applicable regulatory requirements following approval of our product candidate, a regulatory agency may:

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Any government investigation of alleged violations of law could require us to expend significant time and resources in response and could generate negative publicity. The occurrence of any event or penalty described above may inhibit our ability to commercialize CMX001 and our other product candidates and inhibit our ability to generate revenues.

Even if we obtain FDA approval for CMX001 or any of our other products in the United States, we may never obtain approval for or commercialize CMX001 or any of our other products outside of the United States, which would limit our ability to realize their full market potential.

In order to market any products outside of the United States, we must establish and comply with numerous and varying regulatory requirements on a country-by-country basis regarding safety and efficacy. Approval by the FDA does not ensure approval by regulatory authorities in other countries or jurisdictions. In addition, clinical trials conducted in one country may not be accepted by regulatory authorities in other countries, and regulatory approval in one country does not guarantee regulatory approval in any other country. Approval processes vary among countries and can involve additional product testing and validation and additional administrative review periods. Seeking foreign regulatory approval could result in difficulties and costs for us and require additional preclinical studies or clinical trials which could be costly and time consuming. Regulatory requirements can vary widely from country to country and could delay or prevent the introduction of our products in those countries. We do not have any product candidates approved for sale in any jurisdiction, including international markets, and we do not have experience in obtaining regulatory approval in international markets. If we fail to comply with regulatory requirements in international markets or to obtain and maintain required approvals, or if regulatory approvals in international markets are delayed, our target market will be reduced and our ability to realize the full market potential of our products will be unrealized.

Our relationships with customers and payors will be subject to applicable anti-kickback, fraud and abuse and other healthcare laws and regulations, which could expose us to criminal sanctions, civil penalties, contractual damages, reputational harm and diminished profits and future earnings.

Healthcare providers, physicians and others play a primary role in the recommendation and prescription of any products for which we obtain marketing approval. Our future arrangements with third-party payors and customers may expose us to broadly applicable fraud and abuse and other healthcare laws and regulations that may constrain the business or financial arrangements and relationships through which we market, sell and distribute our products for which we obtain marketing approval. Restrictions under applicable federal and state healthcare laws and regulations, include the following:

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Efforts to ensure that our business arrangements with third parties will comply with applicable healthcare laws and regulations will involve substantial costs. It is possible that governmental authorities will conclude that our business practices may not comply with current or future statutes, regulations or case law involving applicable fraud and abuse or other healthcare laws and regulations. If our operations are found to be in violation of any of these laws or any other governmental regulations that may apply to us, we may be subject to significant civil, criminal and administrative penalties, damages, fines, exclusion from government funded healthcare programs, such as Medicare and Medicaid, and the curtailment or restructuring of our operations. If any of the physicians or other providers or entities with whom we expect to do business are found to be not in compliance with applicable laws, they may be subject to criminal, civil or administrative sanctions, including exclusions from government funded healthcare programs.

Recently enacted and future legislation may increase the difficulty and cost for us to obtain marketing approval of and commercialize our product candidates and affect the prices we may obtain.

In the United States and some foreign jurisdictions, there have been a number of legislative and regulatory changes and proposed changes regarding the healthcare system that could prevent or delay marketing approval of our product candidates, restrict or regulate post-approval activities and affect our ability to profitably sell any products for which we obtain marketing approval.

In the United States, the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (Medicare Modernization Act) changed the way Medicare covers and pays for pharmaceutical products. The legislation expanded Medicare coverage for drug purchases by the elderly and introduced a new reimbursement methodology based on average sales prices for physician administered drugs. In addition, this legislation provided authority for limiting the number of drugs that will be covered in any therapeutic class. Cost reduction initiatives and other provisions of this legislation could decrease the coverage and price that we receive for any approved products. While the Medicare Modernization Act applies only to drug benefits for Medicare beneficiaries, private payors often follow Medicare coverage policy and payment limitations in setting their own reimbursement rates. Therefore, any reduction in reimbursement that results from the Medicare Modernization Act may result in a similar reduction in payments from private payors.

More recently, in March 2010, the Health Care Reform Law was enacted to broaden access to health insurance, reduce or constrain the growth of healthcare spending, enhance remedies against fraud and abuse, add new transparency requirements for health care and health insurance industries, impose new taxes and fees on the health industry and impose additional health policy reforms. The Health Care Reform Law revises the definition of “average manufacturer price” for reporting purposes, which could increase the amount of Medicaid drug rebates to states. Further, the new law imposes a significant annual fee on companies that manufacture or import branded prescription drug products. New provisions affecting compliance have also been enacted, which may affect our business practices with health care practitioners. We will not know the full effects of the Health Care Reform Law until applicable federal and state agencies issue regulations or guidance under the new law. Although it is too early to determine the effect of the Health Care Reform Law,

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the new law appears likely to continue the pressure on pharmaceutical pricing, especially under the Medicare program, and may also increase our regulatory burdens and operating costs.

Legislative and regulatory proposals have been made to expand post-approval requirements and restrict sales and promotional activities for pharmaceutical products. We are not sure whether additional legislative changes will be enacted, or whether the FDA regulations, guidance or interpretations will be changed, or what the impact of such changes on the marketing approvals of our product candidates, if any, may be.

Risks Related to Our Reliance on Third Parties

We rely on third-party manufacturers to produce our preclinical and clinical drug supplies, and we intend to rely on third parties to produce commercial supplies of any approved product candidates.

We do not own or operate, and we do not expect to own or operate, facilities for product manufacturing, storage and distribution, or testing. In the past we have relied on third-party manufacturers for supply of our preclinical and clinical drug supplies. We expect that in the future we will continue to rely on such manufacturers for supply of drug supplies that will be used in clinical trials of our product candidates, including CMX001, and for commercialization of any of our product candidates that receive regulatory approval.

Our reliance on third-party manufacturers entails risks to which we would not be subject if we manufactured our product candidates ourselves, including:

Any of these events could lead to clinical study delays, failure to obtain regulatory approval or impact our ability to successfully commercialize our products. Some of these events could be the basis for FDA action, including injunction, recall, seizure, or total or partial suspension of production.

We rely on limited sources of supply for the drug component for our lead product candidate, CMX001, and any disruption in the chain of supply may cause delay in developing and commercializing CMX001.

We are currently transferring the drug substance manufacturing process to our selected contractor that will produce the commercial supply of drug substance and are currently evaluating manufacturers to optimize tablet and suspension formulation production to meet forecasted commercial demand. It is our expectation that

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only one supplier of drug substance and one supplier of drug product will be qualified as vendors with the FDA. If supply from an approved vendor is interrupted, there could be a significant disruption in commercial supply of CMX001. An alternative vendor would need to be qualified through an NDA supplement which could result in further delay. The FDA or other regulatory agencies outside of the United States may also require additional studies if a new drug substance or drug product supplier is relied upon for commercial production.

These factors could cause the delay of clinical trials, regulatory submissions, required approvals or commercialization of CMX001, and cause us to incur additional costs. Furthermore, if our suppliers fail to deliver the required commercial quantities of active pharmaceutical ingredient on a timely basis and at commercially reasonable prices, and we are unable to secure one or more replacement suppliers capable of production at a substantially equivalent cost, our clinical trials for CMX001 may be delayed, which could inhibit our ability to generate revenues.

Manufacturing issues may arise that could increase product and regulatory approval costs or delay commercialization of CMX001.

We have validated the drug substance production process for CMX001 at a manufacturer at a scale of 100 kg, and have validated the manufacturing of clinical trial material at a 165 kg commercial scale. However, we are currently conducting stability studies and analyses that may reveal previously unknown impurities which could require resolution in order to proceed with our planned clinical trials and obtain regulatory approval for the commercial marketing of CMX001. In the future, we may identify significant impurities, which could result in increased scrutiny by the regulatory agencies, delays in clinical program and regulatory approval for CMX001, increases in our operating expenses, or failure to obtain or maintain approval for CMX001.

We depend on the continuation of our current collaboration with Merck, who will develop and commercialize CMX157.

In July 2012, we entered into a collaboration and licensing arrangement with Merck, whereby Merck is responsible for the future development and commercialization of CMX157. Under this arrangement, Merck is responsible for conducting preclinical studies and clinical trials and obtaining required regulatory approvals for CMX157 and manufacturing and commercializing CMX157. Our right to receive milestone and royalty payments under the licensing agreement depends on the achievement of certain development, regulatory and commercial milestones by Merck.

As a result, the development and commercialization of CMX157 would be delayed, and our ability to receive potential milestone and royalty payments under the license agreement with Merck, would be adversely affected if Merck:

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Furthermore, disagreements with Merck could lead to litigation or arbitration, which would be time-consuming and expensive. If any of these issues arise, it may delay the development and commercialization of CMX157 and, ultimately, impair our ability to generate revenues from regulatory and commercialization milestones and royalties based on further development and sales of CMX157.

We rely on third parties to conduct, supervise and monitor our clinical studies, and if those third parties perform in an unsatisfactory manner, it may harm our business.

We rely on contract research organizations (CROs) and clinical trial sites to ensure the proper and timely conduct of our clinical trials. While we have agreements governing their activities, we have limited influence over their actual performance. We have relied and plan to continue to rely upon CROs to monitor and manage data for our ongoing clinical programs for CMX001 and our other product candidates, as well as the execution of nonclinical studies. We control only certain aspects of our CROs’ activities. Nevertheless, we are responsible for ensuring that each of our studies is conducted in accordance with the applicable protocol, legal, regulatory and scientific standards and our reliance on the CROs does not relieve us of our regulatory responsibilities.

We and our CROs are required to comply with the FDA’s guidance, which follows the International Conference on Harmonization Good Clinical Practice (ICH GCP), which are regulations and guidelines enforced by the FDA for all of our product candidates in clinical development. The FDA enforces the ICH GCP through periodic inspections of trial sponsors, principal investigators and clinical trial sites. If we or our CROs fail to comply with the ICH GCP, the clinical data generated in our clinical trials may be deemed unreliable and the FDA may require us to perform additional clinical trials before approving our marketing applications. For example, upon inspection, the FDA may determine that our Phase 3 clinical trial for CMX001, SUPPRESS, does not comply with the ICH GCP. In addition, our Phase 3 clinical trials for CMX001 will require a sufficiently large number of test subjects to evaluate the safety and effectiveness of CMX001. Accordingly, if our CROs fail to comply with these regulations or fail to recruit a sufficient number of subjects, we may be required to repeat these Phase 3 clinical trials, which would delay the regulatory approval process.

Our CROs are not our employees, and we cannot control whether or not they devote sufficient time and resources to our ongoing clinical and nonclinical programs. These CROs may also have relationships with other commercial entities, including our competitors, for whom they may also be conducting clinical studies, or other drug development activities which could harm our competitive position. We face the risk of potential unauthorized disclosure or misappropriation of our intellectual property by CROs, which may reduce our trade secret protection and allow our potential competitors to access and exploit our proprietary technology. If our CROs do not successfully carry out their contractual duties or obligations, fail to meet expected deadlines, or if the quality or accuracy of the clinical data they obtain is compromised due to the failure to adhere to our clinical protocols or regulatory requirements or for any other reasons, our clinical trials may be extended, delayed or terminated, and we may not be able to obtain regulatory approval for, or successfully commercialize CMX001 or our other product candidates. As a result, our financial results and the commercial prospects for CMX001 and any other product candidates that we develop would be harmed, our costs could increase, and our ability to generate revenues could be delayed.

Risks Related to Commercialization of Our Product Candidates

The commercial success of CMX001 and our other product candidates will depend upon the acceptance of these products by the medical community, including physicians, patients and health care payors.

If any of our product candidates, including CMX001, receive marketing approval, they may nonetheless not gain sufficient market acceptance by physicians, patients, healthcare payors and others in the medical community. If these products do not achieve an adequate level of acceptance, we may not generate significant product revenues and we may not become profitable. The degree of market acceptance of any of our product candidates, including CMX001, will depend on a number of factors, including:

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If any of our product candidates, including CMX001, is approved but does not achieve an adequate level of acceptance by physicians, patients and health care payors, we may not generate sufficient revenue and we may not become or remain profitable.

If we are unable to establish sales and marketing capabilities or enter into agreements with third parties to market and sell our product candidates, we may be unable to generate any revenue.

We currently do not have an organization for the sales, marketing and distribution of pharmaceutical products and the cost of establishing and maintaining such an organization may exceed the cost-effectiveness of doing so. In order to market any products that may be approved, including CMX001, we must build our sales, marketing, managerial and other non-technical capabilities or make arrangements with third parties to perform these services. We may enter into strategic partnerships with third parties to commercialize our product candidates outside of the United States, including for CMX001. We intend to build our own sales force and to commercialize CMX001, but we will also consider the option to enter into strategic partnerships for our product candidates in the United States.

Our strategy for CMX001 is to develop a hospital-directed sales force and/or collaborate with third parties to promote the product to healthcare professionals and third-party payors in the United States. Our future collaboration partners, if any, may not dedicate sufficient resources to the commercialization of our product candidates or may otherwise fail in their commercialization due to factors beyond our control. If we are unable to establish effective collaborations to enable the sale of our product candidates to healthcare professionals and in geographical regions, including the United States, that will not be covered by our own marketing and sales force, or if our potential future collaboration partners do not successfully commercialize our product candidates, our ability to generate revenues from product sales, including sales of CMX001, will be adversely affected.

Building an internal sales force involves many challenges, including:

If we are unable to build our own sales force or negotiate a strategic partnership for the commercialization of CMX001 in the United States, we may be forced to delay the potential commercialization of CMX001, reduce the scope of our sales or marketing activities for CMX001 or undertake the commercialization activities for CMX001 at our own expense. If we elect to increase our expenditures to fund commercialization activities ourselves, we will need to obtain additional capital, which may not be available to us on acceptable terms, or at all. If we do not have sufficient funds, we will not be able to bring CMX001 to market or generate product revenue.

If we are unable to establish adequate sales, marketing and distribution capabilities, whether independently or with third parties, we may not be able to generate sufficient product revenue and may not

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become profitable. We will be competing with many companies that currently have extensive and well-funded marketing and sales operations. Without an internal team or the support of a third party to perform marketing and sales functions, we may be unable to compete successfully against these more established companies.

In addition, there are risks involved with both establishing our own sales and marketing capabilities and entering into arrangements with third parties to perform these services. For example, recruiting and training a sales force is expensive and time-consuming and could delay any product launch. If the commercial launch of a product candidate for which we recruit a sales force and establish marketing capabilities is delayed or does not occur for any reason, we would have prematurely or unnecessarily incurred these commercialization expenses. This may be costly, and our investment would be lost if we cannot retain or reposition our sales and marketing personnel.

If we obtain approval to commercialize any products outside of the United States, a variety of risks associated with international operations could materially adversely affect our business.

If our product candidates are approved for commercialization, we intend to enter into agreements with third parties to market those product candidates outside the United States, including for CMX001. We expect that we will be subject to additional risks related to entering into international business relationships, including:

We have no prior experience in these areas. In addition, there are complex regulatory, tax, labor and other legal requirements imposed by both the European Union and many of the individual countries in Europe with which we will need to comply. Many U.S.-based biopharmaceutical companies have found the process of marketing their own products in Europe to be very challenging.

We face significant competition from other biotechnology and pharmaceutical companies and our operating results will suffer if we fail to compete effectively.

The biotechnology and pharmaceutical industries are intensely competitive. We have competitors both in the United States and internationally, including major multinational pharmaceutical companies, biotechnology companies and universities and other research institutions.

Currently the only approved antiviral treatment for CMV in HSCT patients is Cytovene® (ganciclovir), although other antivirals, such as Valcyte® (valganciclovir), Foscavir® (foscarnet), Zovirax® (acyclovir) and Vistide® (cidofovir) are used. Ganciclovir, foscarnet and cidofovir are currently generically available and we expect Valcyte to become generically available in the near-term. We are aware of several companies that are working specifically to develop drugs that would compete against CMX001, including Merck’s development

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of letermovir, Viropharma Incorporated’s development of maribavir and Vical Incorporated’s and Astellas Pharma US, Inc.’s development of TransVax. Many of our competitors have substantially greater financial, technical, commercial and other resources, such as larger research and development staff, stronger intellectual property portfolios and experienced marketing and manufacturing organizations. Additional mergers and acquisitions in the biotechnology and pharmaceutical industries may result in even more resources being concentrated in our competitors.

Competition may increase further as a result of advances in the commercial applicability of technologies and greater availability of capital for investment in these industries. Our competitors may succeed in developing, acquiring or licensing, on an exclusive basis, drug products that are more effective or less costly than CMX001 or any other drug candidate that we are currently developing or that we may develop.

We will face competition from other drugs currently approved or that will be approved in the future for the same indications. Therefore, our ability to compete successfully will depend largely on our ability to:

The availability of our competitors’ products could limit the demand, and the price we are able to charge, for CMX001 and any other product candidate we develop. We will not achieve our business plan if the acceptance of CMX001 is inhibited by price competition or the reluctance of physicians to switch from existing drug products to CMX001, or if physicians switch to other new drug products or choose to reserve CMX001 for use in limited circumstances. The inability to compete with existing or subsequently introduced drug products would have a material adverse impact on our business, financial condition and prospects.

Established pharmaceutical companies may invest heavily to accelerate discovery and development of novel compounds or to in-license novel compounds that could make our product candidates, including CMX001, less competitive. In addition, any new product that competes with an approved product must demonstrate compelling advantages in efficacy, convenience, tolerability and safety in order to overcome price competition and to be commercially successful. Accordingly, our competitors may succeed in obtaining patent protection, receiving FDA approval or discovering, developing and commercializing medicines before we do, which would have a material adverse impact on our business.

Hospital formulary approval and reimbursement may not be available for CMX001 and our other product candidates, which could make it difficult for us to sell our products profitably.

Obtaining hospital formulary approval can be an expensive and time consuming process. We cannot be certain if and when we will obtain formulary approval to allow us to sell our product candidates, including CMX001, into our target markets. Failure to obtain timely formulary approval will limit our commercial success.

Furthermore, market acceptance and sales of CMX001, or any other product candidates that we develop, will depend in part on the extent to which reimbursement for these products and related treatments will be available from government health administration authorities, private health insurers and other organizations. Government authorities and third-party payors, such as private health insurers, hospitals and health maintenance organizations, decide which drugs they will pay for and establish reimbursement levels. Government authorities and third-party payors, such as private health insurers and health maintenance organizations, decide which medications they will pay for and establish reimbursement levels. A primary trend

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in the U.S. healthcare industry and elsewhere is cost containment. Government authorities and these third-party payors have attempted to control costs by limiting coverage and the amount of reimbursement for particular medications. Increasingly, third-party payors are requiring that companies provide them with predetermined discounts from list prices and are challenging the prices charged for medical products. We cannot be sure that reimbursement will be available for any product that we commercialize and, if reimbursement is available, what the level of reimbursement will be. Reimbursement may impact the demand for, or the price of, any product for which we obtain marketing approval. Obtaining reimbursement for our products may be particularly difficult because of the higher prices often associated with products administered under the supervision of a physician. We cannot be sure that reimbursement will be available for CMX001, or any other product candidates. Also, reimbursement amounts may reduce the demand for, or the price of, our products. If reimbursement is not available, or is available only to limited levels, we may not be able to successfully commercialize CMX001, or any other product candidates that we develop.

There have been a number of legislative and regulatory proposals to change the healthcare system in the United States and in some foreign jurisdictions that could affect our ability to sell any future products profitably. These legislative and regulatory changes may negatively impact the reimbursement for any future products, following approval. The availability of generic treatments may also substantially reduce the likelihood of reimbursement for any future products, including CMX001. The application of user fees to generic drug products will likely expedite the approval of additional generic drug treatments. We expect to experience pricing pressures in connection with the sale of CMX001 and any other product candidate that we develop, due to the trend toward managed healthcare, the increasing influence of health maintenance organizations and additional legislative changes.

In addition, there may be significant delays in obtaining reimbursement for approved products, and coverage may be more limited than the purposes for which the product is approved by the FDA or regulatory authorities in other countries. Moreover, eligibility for reimbursement does not imply that any product will be paid for in all cases or at a rate that covers our costs, including research, development, manufacture, sale and distribution. Interim payments for new products, if applicable, may also not be sufficient to cover our costs and may not be made permanent. Payment rates may vary according to the use of the product and the clinical setting in which it is used, may be based on payments allowed for lower cost products that are already reimbursed, and may be incorporated into existing payments for other services. Net prices for products may be reduced by mandatory discounts or rebates required by government healthcare programs or private payors and by any future relaxation of laws that presently restrict imports of products from countries where they may be sold at lower prices than in the United States. Third-party payors often rely upon Medicare coverage policy and payment limitations in setting their own reimbursement policies.

Our inability to promptly obtain coverage and profitable payment rates from both government funded and private payors for any of our product candidates, including CMX001, could have a material adverse effect on our operating results, our ability to raise capital needed to commercialize products and our overall financial condition.

We may expend our limited resources to pursue a particular product candidate or indication and fail to capitalize on product candidates or indications that may be more profitable or for which there is a greater likelihood of success.

The success of our business depends primarily upon our ability to identify, develop and commercialize product candidates. Because we have limited financial and managerial resources, we focus on research programs and product candidates for specific indications. As a result, we may forego or delay pursuit of opportunities with other product candidates or other indications that later prove to have greater commercial potential. Our research programs may initially show promise in identifying potential product candidates, yet fail to yield product candidates for clinical development for a number of reasons, including:

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If any of these events occur, we may be forced to abandon our development efforts for a program or programs, which would have a material adverse effect on our business and could potentially cause us to cease operations. Research programs to identify new product candidates require substantial technical, financial and human resources. We may focus our research efforts and resources on potential programs or product candidates that ultimately prove to be unsuccessful.

If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through collaboration, licensing or other royalty arrangements in cases in which it would have been advantageous for us to retain sole development and commercialization rights.

Risks Related to Our Intellectual Property

If we are unable to obtain or protect intellectual property rights related to our products and product candidates, we may not be able to compete effectively in our market.

We rely upon a combination of patents, trade secret protection and confidentiality agreements to protect the intellectual property related to our products and product candidates. The strength of patents in the biotechnology and pharmaceutical field involves complex legal and scientific questions and can be uncertain. The patent applications that we own or in-license may fail to result in issued patents with claims that cover the products in the United States or in other countries. If this were to occur, early generic competition could be expected against CMX001, CMX157 and other product candidates in development. There is no assurance that all of the potentially relevant prior art relating to our patents and patent applications has been found, which can invalidate a patent or prevent a patent from issuing based on a pending patent application. Even if patents do successfully issue, third parties may challenge their validity, enforceability, scope or ownership, which may result in such patents, or our rights to such patents, being narrowed or invalidated. Furthermore, even if they are unchallenged, our patents and patent applications, may not adequately protect our intellectual property or prevent others from designing around our claims. If the patent applications we hold or license with respect to CMX001 and CMX157 fail to issue or if their breadth or strength of protection is threatened, it could dissuade companies from collaborating with us to develop, and threaten our ability to commercialize, our products. We cannot offer any assurances about which, if any, patents will issue or whether any issued patents will be found not invalid and not unenforceable, will go unthreatened by third parties or will adequately protect our products and product candidates. Further, if we encounter delays in regulatory approvals, the period of time during which we could market CMX001 and CMX157 under patent protection could be reduced. Since patent applications in the United States and most other countries are confidential for a period of time after filing, and some remain so until issued, we cannot be certain that we or our licensors were the first to file any patent application related to CMX001, CMX157 or our other product candidates. Furthermore, if third parties have filed such patent applications, an interference proceeding in the United States can be provoked by a third party or instituted by us to determine who was the first to invent any of the subject matter covered by the patent claims of our applications. An unfavorable outcome could require us to cease using the related technology or to attempt to license it from the prevailing party, which may not be possible.

In addition to the protection afforded by patents, we rely on trade secret protection and confidentiality agreements to protect proprietary know-how that is not patentable, processes for which patents are difficult to enforce and other elements of our drug discovery and development processes that involve proprietary know-how, information or technology that is not covered by patents. Although we expect all of our employees to assign their inventions to us, and all of our employees, consultants, advisors and any third parties who have access to our proprietary know-how, information or technology to enter into confidentiality agreements, we cannot provide any assurances that all such agreements have been duly executed, that such agreements provide adequate protection and will not be breached, that our trade secrets and other confidential proprietary information will not otherwise be disclosed or that competitors will not otherwise gain access to our trade secrets or independently develop substantially equivalent information and techniques. If we are unable to prevent material disclosure of the non-patented intellectual property related to our technologies to third parties,

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and there is no guarantee that we will have any such enforceable trade secret protection, we may not be able to establish or maintain a competitive advantage in our market, which could materially adversely affect our business, results of operations and financial condition.

Further, the laws of some foreign countries do not protect patents and other proprietary rights to the same extent or in the same manner as the laws of the United States. As a result, we may encounter significant problems in protecting and defending our intellectual property abroad. We may also fail to pursue or obtain patents and other intellectual property protection relating to our products and product candidates in all foreign countries.

Finally, certain of our activities and our licensors’ activities have been funded, and may in the future be funded, by the U.S. federal government. When new technologies are developed with U.S. federal government funding, the government obtains certain rights in any resulting patents, including a nonexclusive license authorizing the government to use the invention for non-commercial purposes. These rights may permit the government to disclose our confidential information to third parties and to exercise “march-in” rights to use or allow third parties to use our patented technology. The government can exercise its march-in rights if it determines that action is necessary because we fail to achieve practical application of the U.S. government-funded technology, because action is necessary to alleviate health or safety needs, to meet requirements of federal regulations or to give preference to U.S. industry. In addition, U.S. government-funded inventions must be reported to the government, U.S. government funding must be disclosed in any resulting patent applications, and our rights in such inventions may be subject to certain requirements to manufacture products in the United States.

Third-party claims of intellectual property infringement may prevent or delay our development and commercialization efforts or otherwise affect our business.

Our commercial success depends in part on our avoiding infringement and other violations of the patents and proprietary rights of third parties. There is a substantial amount of litigation, both within and outside the United States, involving patent and other intellectual property rights in the biotechnology and pharmaceutical industries, including patent infringement lawsuits, interferences, oppositions and inter party reexamination proceedings before the United States Patent and Trademark Office (U.S. PTO) and its foreign counterparts. Numerous U.S. and foreign issued patents and pending patent applications, which are owned by third parties, exist in the fields in which we and our collaborators are developing product candidates. As the biotechnology and pharmaceutical industries expand and more patents are issued, and as we gain greater visibility and market exposure as a public company, the risk increases that our product candidates or other business activities may be subject to claims of infringement of the patent and other proprietary rights of third parties.

Third parties may assert that we are employing their proprietary technology without authorization. There may be third-party patents or patent applications with claims to materials, formulations, methods of manufacture or methods for treatment related to the use or manufacture of CMX001 and CMX157 and/or our other product candidates. Because patent applications can take many years to issue, there may be currently pending patent applications which may later result in issued patents that our product candidates may infringe. In addition, third parties may obtain patents in the future and claim that use of our technologies infringes upon these patents. If any third-party patents were held by a court of competent jurisdiction to cover the manufacturing process of any of our product candidates, any molecules formed during the manufacturing process or any final product itself, the holders of any such patents may be able to block our ability to commercialize such product candidate unless we obtained a license under the applicable patents, or until such patents expire. Similarly, if any third-party patent were held by a court of competent jurisdiction to cover aspects of our formulations, processes for manufacture or methods of use, including combination therapy, the holders of any such patent may be able to block our ability to develop and commercialize the applicable product candidate unless we obtained a license or until such patent expires. In either case, such a license may not be available on commercially reasonable terms or at all. In addition, we may be subject to claims that we are infringing other intellectual property rights, such as trademarks or copyrights, or misappropriating the trade secrets of others, and to the extent that our employees, consultants or contractors use intellectual property or proprietary information owned by others in their work for us, disputes may arise as to the rights in related or resulting know-how and inventions.

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Parties making claims against us may obtain injunctive or other equitable relief, which could effectively block our ability to further develop and commercialize one or more of our product candidates. Defense of these claims, regardless of their merit, would involve substantial litigation expense and would be a substantial diversion of employee resources from our business. In the event of a successful infringement or other intellectual property claim against us, we may have to pay substantial damages, including treble damages and attorneys’ fees for willful infringement, obtain one or more licenses from third parties, pay royalties or redesign our affected products, which may be impossible or require substantial time and monetary expenditure. We cannot predict whether any such license would be available at all or whether it would be available on commercially reasonable terms. Furthermore, even in the absence of litigation, we may need to obtain licenses from third parties to advance our research or allow commercialization of our product candidates, and we have done so from time to time. We may fail to obtain any of these licenses at a reasonable cost or on reasonable terms, if at all. In that event, we would be unable to further develop and commercialize one or more of our product candidates, which could harm our business significantly. We cannot provide any assurances that third-party patents do not exist which might be enforced against our products or product candidates, resulting in either an injunction prohibiting our sales, or, with respect to our sales, an obligation on our part to pay royalties and/or other forms of compensation to third parties.

We license certain key intellectual property from third parties, and the loss of our license rights could have a materially adverse effect on our business.

We are a party to a number of technology licenses that are important to our business and expect to enter into additional licenses in the future. For example, we rely on an exclusive license to certain patents, proprietary technology and know-how from The Regents of the University of California (UC), which we believe cover CMX001 and CMX157. If we fail to comply with our obligations under our agreement with UC or our other license agreements, or we are subject to a bankruptcy, the licensor may have the right to terminate the license, in which event we would not be able to develop or market products covered by the license, including in the case of the UC license, CMX001 and CMX157, which would have a materially adverse effect on our business.

We may be involved in lawsuits to protect or enforce our patents, the patents of our licensors or our other intellectual property rights, which could be expensive, time consuming and unsuccessful.

Competitors may infringe or otherwise violate our patents, the patents of our licensors or our other intellectual property rights. To counter infringement or unauthorized use, we may be required to file legal claims, which can be expensive and time-consuming. In addition, in an infringement proceeding, a court may decide that a patent of ours or our licensors is not valid or is unenforceable, or may refuse to stop the other party from using the technology at issue on the grounds that our patents do not cover the technology in question. An adverse result in any litigation or defense proceedings could put one or more of our patents at risk of being invalidated or interpreted narrowly and could put our patent applications at risk of not issuing. The initiation of a claim against a third party may also cause the third party to bring counter-claims against us.

We may not be able to prevent, alone or with our licensors, misappropriation of our intellectual property rights, particularly in countries where the laws may not protect those rights as fully as in the United States. Our business could be harmed if in a litigation the prevailing party does not offer us a license on commercially reasonable terms. Any litigation or other proceedings to enforce our intellectual property rights may fail, and even if successful, may result in substantial costs and distract our management and other employees.

Furthermore, because of the substantial amount of discovery required in connection with intellectual property litigation, there is a risk that some of our confidential information could be compromised by disclosure during this type of litigation. There could also be public announcements of the results of hearings, motions or other interim proceedings or developments. If securities analysts or investors perceive these results to be negative, it could have a material adverse effect on the price of our common stock.

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Obtaining and maintaining our patent protection depends on compliance with various procedural, document submission, fee payment and other requirements imposed by governmental patent agencies, and our patent protection could be reduced or eliminated for non-compliance with these requirements.

Periodic maintenance fees on any issued patent are due to be paid to the U.S. PTO and foreign patent agencies in several stages over the lifetime of the patent. The U.S. PTO and various foreign governmental patent agencies require compliance with a number of procedural, documentary, fee payment and other similar provisions during the patent application process. While an inadvertent lapse can in many cases be cured by payment of a late fee or by other means in accordance with the applicable rules, there are situations in which noncompliance can result in abandonment or lapse of the patent or patent application, resulting in partial or complete loss of patent rights in the relevant jurisdiction. Non-compliance events that could result in abandonment or lapse of a patent or patent application include, but are not limited to, failure to respond to official actions within prescribed time limits, non-payment of fees and failure to properly legalize and submit formal documents. If we or our licensors that control the prosecution and maintenance of our licensed patents fail to maintain the patents and patent applications covering our product candidates, we may lose our rights and our competitors might be able to enter the market, which would have a material adverse effect on our business.

Risks Related to Our United States Government Contracts and Grants

All of our immediately foreseeable future revenues to support the development of CMX001 for the treatment of smallpox are dependent upon our contract with BARDA, and if we do not receive all of the funds under the BARDA contract we anticipate that we will suspend or terminate our smallpox program.

Substantially all of our revenues that support the development of CMX001 for the treatment of smallpox have been derived from prior government grants and our current contract with BARDA. Our contract with BARDA is for the development of CMX001 for the treatment of smallpox. It is divided into a base segment and four option segments. We are currently performing the base segment of the contract. BARDA has the right, exercisable in its sole discretion, to extend the contract for successive option segments following the base segment. We anticipate renegotiating certain aspects of the smallpox animal plan to take into account recent guidance from the FDA for development of CMX001 under the FDA’s Animal Efficacy Rule. There can be no assurance that we will reach agreement with BARDA on the most appropriate development pathway or that the FDA will ultimately agree with the experiments which we perform or the appropriateness of the results of these experiments for licensure of CMX001 for smallpox. We do not anticipate continuing this program without ongoing support from BARDA.

Additionally, the contract provides for reimbursement of the costs of the development of CMX001 for the treatment of smallpox that are allowable under the Federal Acquisition Regulation (FAR), plus the payment of a fixed fee. It does not include the manufacture of CMX001 for the Strategic National Stockpile. There can be no assurances that this contract will continue, that BARDA will extend the contract for successive option segments following the base segment, that any such extension would be on favorable terms, or that we will be able to enter into new contracts with the United States government to support our smallpox program. Changes in government budgets and agendas may result in a decreased and de-prioritized emphasis on supporting the discovery and development of CMX001 for the treatment of smallpox. In such event, BARDA is not required to continue funding our existing contract. Any such reduction in our revenues from BARDA or any other government contract could materially adversely affect our financial condition and results of operations. In addition, if we do not receive all of the funds under the BARDA contract, we anticipate that we will suspend or terminate our program for the development of CMX001 for the treatment of smallpox.

Unfavorable provisions in government contracts, including our contract with BARDA, may harm our business, financial condition and operating results.

United States government contracts typically contain unfavorable provisions and are subject to audit and modification by the government at its sole discretion, which will subject us to additional risks. For example, under our contract with BARDA, the U.S. government has the power to unilaterally:

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The U.S. government also has the right to terminate the BARDA contract if termination is in the government’s interest, or if we default by failing to perform in accordance with the milestones set forth in the contract. Termination-for-convenience provisions generally enable us to recover only our costs incurred or committed (plus a portion of the agreed fee) and settlement expenses on the work completed prior to termination. Except for the amount of services received by the government, termination-for-default provisions do not permit recovery of fees.

In addition, we must comply with numerous laws and regulations that affect how we conduct business with the United States government. Among the most significant government contracting regulations that affect our business are:

Furthermore, we may be required to enter into agreements and subcontracts with third parties, including suppliers, consultants and other third-party contractors, in order to satisfy our contractual obligations pursuant to our agreements with the U.S. government. Negotiating and entering into such arrangements can be time-consuming and we may not be able to reach agreement with such third parties. Any such agreement must also be compliant with the terms of our government contract. Any delay or inability to enter into such arrangements or entering into such arrangements in a manner that is non-compliant with the terms of our contract, may result in violations of our contract.

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As a result of these unfavorable provisions, we must undertake significant compliance activities. The diversion of resources from commercial programs to these compliance activities, as well as the exercise by the U.S. government of any rights under these provisions, could materially harm our business.

Our business is subject to audit by the U.S. government, including under our contract with BARDA, and a negative audit could adversely affect our business.

United States government agencies such as the Department of Health and Human Services (DHHS), routinely audit and investigate government contractors and recipients of federal grants, including our contract with BARDA. These agencies review a contractor’s performance under its contracts, cost structure and compliance with applicable laws, regulations and standards.

The DHHS can also review the adequacy of, and a contractor’s compliance with, its internal control systems and policies, including the contractor’s purchasing, property, estimating, compensation and management information systems. Any costs found to be improperly allocated to a specific contract will not be reimbursed, while such costs already reimbursed must be refunded. If an audit uncovers improper or illegal activities, we may be subject to civil and criminal penalties and administrative sanctions, including:

In addition, we could suffer serious reputational harm if allegations of impropriety were made against us by the U.S. government, which could adversely affect our business.

Agreements with government agencies may lead to claims against us under the Federal False Claims Act, and these claims could result in substantial fines and other penalties.

The biopharmaceutical industry is, and in recent years has been, under heightened scrutiny as the subject of government investigations and enforcement actions. Our BARDA contract is subject to substantial financial penalties under the Federal Civil Monetary Penalties Act and the Federal Civil False Claims Act (False Claims Act). Under the False Claims Act’s “whistleblower” provisions, private enforcement of fraud claims against businesses on behalf of the U.S. government has increased due in part to amendments to the False Claims Act that encourage private individuals to sue on behalf of the government. These whistleblower suits, known as qui tam actions, may be filed by private individuals, including present and former employees. The False Claims Act provides for treble damages and up to $11,000 per false claim. If our operations are found to be in violation of any of these laws, or any other governmental regulations that apply to us, we may be subject to penalties, including civil and criminal penalties, damages, fines, exclusion from the Medicare and Medicaid programs, and the curtailment or restructuring of our operations. Any penalties, damages, fines, exclusions, curtailment, or restructuring of our operations could adversely affect our ability to operate our business and our financial results.

Risks Related to Our Business Operations and Industry

Our future success depends on our ability to retain key executives and to attract, retain and motivate qualified personnel.

We are highly dependent on principal members of our executive team listed under “Management.” While we have entered into employment agreements or offer letters with each of our executive officers, any of them could leave our employment at any time, as all of our employees are “at will” employees. We do not maintain “key person” insurance for any of our executives or other employees. Recruiting and retaining other qualified employees for our business, including scientific and technical personnel, will also be critical to our success. There is currently a shortage of skilled executives in our industry, which is likely to continue. We also experience competition for the hiring of scientific and clinical personnel from universities and research

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institutions. As a result, competition for skilled personnel is intense and the turnover rate can be high. We may not be able to attract and retain personnel on acceptable terms given the competition among numerous pharmaceutical and biotechnology companies for similar personnel. In addition, failure of any of our clinical studies may make it more challenging to recruit and retain qualified personnel. The inability to recruit or loss of the services of any executive or key employee may adversely affect the progress of our research, development and commercialization objectives.

In addition, we rely on consultants and advisors, including scientific and clinical advisors, to assist us in formulating our research and development and commercialization strategy. Our consultants and advisors may be employed by employers other than us and may have commitments under consulting or advisory contracts with other entities that may limit their availability to us, which could also adversely affect the progress of our research, development and commercialization objectives.

We will need to expand our organization, and we may experience difficulties in managing this growth, which could disrupt our operations.

As of December 31, 2012, we had 46 full-time employees. As our company matures, we expect to expand our employee base to increase our managerial, clinical, scientific and engineering, operational, sales, and marketing teams. Future growth would impose significant additional responsibilities on our management, including the need to identify, recruit, maintain, motivate and integrate additional employees, consultants and contractors. Also, our management may need to divert a disproportionate amount of its attention away from our day-to-day activities and devote a substantial amount of time to managing these growth activities. We may not be able to effectively manage the expansion of our operations, which may result in weaknesses in our infrastructure, give rise to operational mistakes, loss of business opportunities, loss of employees and reduced productivity among remaining employees. Our expected growth could require significant capital expenditures and may divert financial resources from other projects, such as the development of product candidates. If our management is unable to effectively manage our growth, our expenses may increase more than expected, our ability to generate and/or grow revenues could be reduced, and we may not be able to implement our business strategy. Our future financial performance and our ability to commercialize CMX001 and our other product candidates and compete effectively will depend, in part, on our ability to effectively manage any future growth.

Potential product liability lawsuits against us could cause us to incur substantial liabilities and to limit commercialization of any products that we may develop.

The use of our product candidates, including CMX001, in clinical studies and the sale of any products for which we obtain marketing approval exposes us to the risk of product liability claims. Product liability claims might be brought against us by consumers, health care providers, pharmaceutical companies or others selling or otherwise coming into contact with our products. On occasion, large judgments have been awarded in class action lawsuits based on drugs that had unanticipated adverse effects. If we cannot successfully defend against product liability claims, we could incur substantial liability and costs. In addition, regardless of merit or eventual outcome, product liability claims may result in:

We currently carry $5.0 million in product liability insurance covering our clinical trials. Our current product liability insurance coverage may not be sufficient to reimburse us for any expenses or losses we may suffer. Moreover, insurance coverage is becoming increasingly expensive and in the future we may not be able

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to maintain insurance coverage at a reasonable cost or in sufficient amounts to protect us against losses due to liability. If and when we obtain marketing approval for our product candidates, we intend to expand our insurance coverage to include the sale of commercial products; however, we may be unable to obtain product liability insurance on commercially reasonable terms or in adequate amounts. A successful product liability claim or series of claims brought against us could cause our stock price to decline and, if judgments exceed our insurance coverage, could adversely affect our results of operations and business.

Risks Related to this Offering and Ownership of Our Common Stock

The market price of our common stock is likely to be volatile, and you may not be able to resell your shares at or above the initial public offering price.

The trading price of our common stock is likely to be volatile. Our stock price could be subject to wide fluctuations in response to a variety of factors, including the following:

In addition, the stock market in general, and the Nasdaq Global Market in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of these companies. Broad market and industry factors may negatively affect the market price of our common stock, regardless of our actual operating performance.

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An active trading market for our common stock may not develop.

Prior to this offering, there has not been a public market for our common stock. Although our common stock has been approved for listing on the Nasdaq Global Market, an active trading market for our shares may never develop or be sustained following this offering. Entities affiliated with certain of our existing stockholders and directors have indicated an interest in purchasing up to an aggregate of approximately $     million in shares of our common stock in this offering at the initial public offering price. To the extent these potential investors are allocated and purchase shares in this offering, such purchases would reduce the available public float for our shares because these potential investors will be restricted from selling the shares under the lock-up agreements described in the “Shares Eligible for Future Sale” section of this prospectus. As a result, the liquidity of our common stock could be significantly reduced from what it would have been if these shares had been purchased by investors that were not affiliated with us. If an active market for our common stock does not develop, you may not be able to sell your shares quickly or at the market price. The initial public offering price for the shares will be determined by negotiations between us and representatives of the underwriters and may not be indicative of prices that will prevail in the trading market.

Our principal stockholders and management own a significant percentage of our stock and will be able to exert significant control over matters subject to stockholder approval.

Our executive officers, directors, 5% stockholders and their affiliates beneficially own approximately 81% of our voting stock and, upon the closing of this offering, that same group will beneficially own approximately     % of our voting stock, excluding any shares of our common stock that these stockholders may purchase in the offering. Therefore, even after this offering these stockholders will have the ability to substantially influence us through this ownership position. For example, these stockholders, if they choose to act together, may be able to control elections of directors, amendments of our organizational documents, or approval of any merger, sale of assets, or other major corporate transaction. This concentration of voting power could delay or prevent an acquisition of our company on terms that other stockholders may desire.

We are an “emerging growth company,” and we cannot be certain if the reduced reporting requirements applicable to emerging growth companies will make our common stock less attractive to investors.

We are an “emerging growth company,” as defined in the JOBS Act. For as long as we continue to be an emerging growth company, we may take advantage of exemptions from various reporting requirements that are applicable to other public companies that are not “emerging growth companies,” including exemption from compliance with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act of 2002 (Sarbanes-Oxley Act), reduced disclosure obligations regarding executive compensation in this prospectus and our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved. We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of this offering, (b) in which we have total annual gross revenue of at least $1.0 billion, or (c) in which we are deemed to be a large accelerated filer, which means the market value of our common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30th, and (2) the date on which we have issued more than $1.0 billion in non-convertible debt during the prior three-year period.

Even after we no longer qualify as an emerging growth company, we may still qualify as a “smaller reporting company” which would allow us to take advantage of many of the same exemptions from disclosure requirements including exemption from compliance with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act and reduced disclosure obligations regarding executive compensation in this prospectus and our periodic reports and proxy statements. We cannot predict if investors will find our common stock less attractive because we may rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stock and our stock price may be more volatile.

Under the JOBS Act, emerging growth companies can also delay adopting new or revised accounting standards until such time as those standards apply to private companies. We have irrevocably elected not to

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avail ourselves of this exemption from new or revised accounting standards and, therefore, will be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies.

We will incur significant increased costs as a result of operating as a public company, and our management will be required to devote substantial time to new compliance initiatives.

As a public company, we will incur significant legal, accounting and other expenses that we did not incur as a private company. In addition, the Sarbanes-Oxley Act, as well as rules subsequently implemented by the Securities and Exchange Commission (SEC), and the Nasdaq Global Market have imposed various requirements on public companies. In July 2010, the Dodd-Frank Wall Street Reform and Consumer Protection Act (Dodd-Frank Act), was enacted. There are significant corporate governance and executive compensation related provisions in the Dodd-Frank Act that require the SEC to adopt additional rules and regulations in these areas such as “say on pay” and proxy access. Stockholder activism, the current political environment and the current high level of government intervention and regulatory reform may lead to substantial new regulations and disclosure obligations, which may lead to additional compliance costs and impact (in ways we cannot currently anticipate) the manner in which we operate our business. Our management and other personnel will need to devote a substantial amount of time to these compliance initiatives. Moreover, these rules and regulations will increase our legal and financial compliance costs and will make some activities more time-consuming and costly. For example, we expect that these rules and regulations will make it more difficult and more expensive for us to obtain director and officer liability insurance and we may be required to incur substantial costs to maintain our current levels of such coverage.

If you purchase our common stock in this offering, you will incur immediate and substantial dilution in the book value of your shares.

Investors purchasing common stock in this offering will pay a price per share that substantially exceeds the pro forma book value (deficit) per share of our tangible assets after subtracting our liabilities. As a result, investors purchasing common stock in this offering will incur immediate dilution of $   per share, based on an assumed initial public offering price of $     per share (the mid-point of the price range set forth on the cover page of this prospectus) and our pro forma net tangible book value (deficit) as of December 31, 2012. Further, based on these assumptions, investors purchasing common stock in this offering will contribute approximately    % of the total amount invested by stockholders since our inception, but will own only approximately    % of the shares of common stock outstanding. For information on how the foregoing amounts were calculated, see “Dilution.”

This dilution is due to the substantially lower price paid by our investors who purchased shares prior to this offering as compared to the price offered to the public in this offering, and the exercise of stock options granted to our employees. In addition, as of December 31, 2012, options to purchase 2,593,423 shares of our common stock at a weighted-average exercise price of $2.45 per share were outstanding, restricted stock units to acquire 43,199 shares of our common stock were outstanding and warrants to purchase 1,613,395 shares of our common stock at a weighted-average exercise price of $7.26 per share were outstanding. The exercise of any of these options or warrants, and the issuance of shares pursuant to these restricted stock units (which will vest in connection with the consummation of this offering), would result in additional dilution. As a result of the dilution to investors purchasing shares in this offering, investors may receive significantly less than the purchase price paid in this offering, if anything, in the event of our liquidation.

A significant portion of our total outstanding shares are restricted from immediate resale but may be sold into the market in the near future. This could cause the market price of our common stock to drop significantly, even if our business is doing well.

Sales of a substantial number of shares of our common stock in the public market or the perception that these sales might occur, could depress the market price of our common stock and could impair our ability to raise capital through the sale of additional equity securities. We are unable to predict the effect that sales may have on the prevailing market price of our common stock.

After this offering, we will have outstanding       shares of common stock based on the number of shares outstanding as of December 31, 2012. This includes the shares that we are selling in this offering,

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which may be resold in the public market immediately without restriction, unless purchased by our affiliates. Of the remaining shares, shares are currently restricted as a result of securities laws or lock-up agreements but will be able to be sold after the offering as described under the “Shares Eligible for Future Sale.”

Substantially all of our existing stockholders, optionholders, restricted stock unit holders and warrantholders are subject to lock-up agreements with the underwriters of this offering that restrict their ability to transfer shares of our common stock or securities convertible into or exercisable or exchangeable for shares of our common stock for at least 180 days from the date of this prospectus. The lock-up agreements limit the number of shares of common stock that may be sold immediately following the public offering. Subject to certain limitations, approximately     shares will become eligible for sale upon expiration of the lock-up period, as calculated and described in more detail in the section entitled “Shares Eligible for Future Sale.” In addition, shares issued or issuable upon exercise of options, restricted stock units and warrants vested as of the expiration of the lock-up period will be eligible for sale at that time. Sales of stock by these stockholders could have a material adverse effect on the trading price of our common stock.

Certain holders of our securities are entitled to rights with respect to the registration of their shares under the Securities Act, subject to the 180-day lock-up arrangement described above. At any time after 180 days of this offering but not before six months after this offering, holders of the registrable securities then outstanding, will have rights, subject to some conditions, to require us to file registration statements covering their shares or to include their shares in registration statements that we may file for ourselves or other stockholders. Registration of these shares under the Securities Act would result in the shares becoming freely tradable without restriction under the Securities Act, except for shares held by our affiliates as defined in Rule 144 under the Securities Act. Any sales of securities by these stockholders could have a material adverse effect on the trading price of our common stock.

We also intend to register all shares of common stock that we may issue under our equity compensation plans. Once we register these shares, they can be freely sold in the public market upon issuance, subject to volume limitations applicable to affiliates and the lock-up agreements described in the “Underwriting” section of this prospectus.

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds, including for any of the purposes described in the section entitled “Use of Proceeds,” and you will not have the opportunity as part of your investment decision to assess whether our management are using the net proceeds appropriately. Because of the number and variability of factors that will determine our use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. The failure by our management to apply these funds effectively could result in financial losses that could have a material adverse effect on our business, cause the price of our common stock to decline and delay the development of our product candidates. Pending their use, we may invest the net proceeds from this offering in short-term, investment-grade, interest-bearing securities. These investments may not yield a favorable return to our stockholders.

Volatility in our stock price could subject us to securities class action litigation.

In the past, securities class action litigation has often been brought against a company following a decline in the market price of its securities. This risk is especially relevant for us because pharmaceutical companies have experienced significant stock price volatility in recent years. If we face such litigation, it could result in substantial costs and a diversion of management’s attention and resources, which could harm our business.

Our ability to use our net operating loss carryforwards and certain other tax attributes may be limited.

Under Section 382 of the Internal Revenue Code of 1986, as amended (Code), if a corporation undergoes an “ownership change,” generally defined as a greater than 50% change (by value) in its equity ownership over a three year period, the corporation’s ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes (such as research tax credits) to offset its post-change income may be limited. We have determined that a Section 382 ownership change occurred in 2002 and 2007 resulting in limitations

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of at least $64,000 and $762,000, respectively, of losses incurred prior to the respective ownership change dates. We believe that, with our initial public offering, our most recent private placement and other transactions that have occurred since 2007, we may have triggered an ownership change limitation. We may also experience ownership changes in the future as a result of subsequent shifts in our stock ownership. As a result, if we earn net taxable income, our ability to use our pre-change net operating loss carryforwards to offset United States federal taxable income may be subject to limitations, which could potentially result in increased future tax liability to us.

Because we do not anticipate paying any cash dividends on our common stock in the foreseeable future, capital appreciation, if any, would be your sole source of gain.

We have never declared or paid any cash dividends on our common stock. We currently anticipate that we will retain future earnings for the development, operation and expansion of our business and do not anticipate declaring or paying any cash dividends for the foreseeable future. As a result, capital appreciation, if any, of our common stock would be your sole source of gain on an investment in our common stock for the foreseeable future.

Provisions in our corporate charter documents and under Delaware law could make it more difficult for a third party to acquire us or increase the cost of acquiring us, even if doing so would benefit our stockholders and may prevent attempts by our stockholders to replace or remove our current management.

Some provisions of our charter documents and Delaware law may have anti-takeover effects that could discourage an acquisition of us by others, even if an acquisition would be beneficial to our stockholders and may prevent attempts by our stockholders to replace or remove our current management. These provisions include:

The amendment of any of these provisions, with the exception of the ability of our board of directors to issue shares of preferred stock and designate any rights, preferences and privileges thereto, would require the affirmative vote of the holders of at least 66 2/3% of the voting power of all of our then outstanding common stock.

These provisions may frustrate or prevent any attempts by our stockholders to replace or remove our current management by making it more difficult for stockholders to replace members of our board of directors, which is responsible for appointing the members of our management. In addition, we are subject to Section 203 of the Delaware General Corporation Law, which generally prohibits a Delaware corporation from engaging in any of a broad range of business combinations with an interested stockholder for a period of three years following the date on which the stockholder became an interested stockholder, unless such transactions are approved by our board of directors. This provision could have the effect of delaying or preventing a change of control, whether or not it is desired by or beneficial to our stockholders. Further, other provisions of Delaware law may also discourage, delay or prevent someone from acquiring us or merging with us.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, including the sections entitled “Prospectus Summary,” “Risk Factors,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Business,” contains forward-looking statements. We may, in some cases, use word such as “anticipate,” “believe,” “could,” “estimate,” “expects,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” or the negative of those terms, and similar expressions that convey uncertainty of future events or outcomes to identify these forward-looking statements. Any statements contained herein that are not statements of historical facts may be deemed to be forward-looking statements. Forward-looking statements in this prospectus include, but are not limited to, statements about:

These forward-looking statements reflect our management’s beliefs and views with respect to future events and are based on estimates and assumptions as of the date of this prospectus and are subject to risks and uncertainties. We discuss many of these risks in greater detail under “Risk Factors.” Moreover, we operate in a very competitive and rapidly changing environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. Given these uncertainties, you should not place undue reliance on these forward-looking statements.

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You should read this prospectus and the documents that we reference in this prospectus and have filed as exhibits to the registration statement, of which this prospectus is a part, completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in this prospectus by these cautionary statements. Except as required by law, we undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise.

MARKET, INDUSTRY AND OTHER DATA

This prospectus also contains estimates, projections and other information concerning our industry, our business and relevant antiviral markets, including data regarding the estimated size of relevant antiviral markets, patient populations, projected diagnosis rates and the perceptions and preferences of patients and physicians regarding certain therapies, as well as data regarding market research and estimates. Information that is based on estimates, forecasts, projections, market research or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances that are assumed in this information. Unless otherwise expressly stated, we obtained this industry, business, market and other data from reports, research surveys, studies and similar data prepared by market research firms and other third parties, industry, medical and general publications, government data and similar sources that we believe to be reliable. In some cases, we do not expressly refer to the sources from which this data is derived. In that regard, when we refer to one or more sources of this type of data in any paragraph, you should assume that other data of this type appearing in the same paragraph is derived from the same sources, unless otherwise expressly stated or the context otherwise requires.

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USE OF PROCEEDS

We estimate that we will receive net proceeds of approximately $      million (or approximately $      million if the underwriters’ over-allotment option is exercised in full) from the sale of the shares of common stock offered by us in this offering, based on an assumed initial public offering price of $      per share (the mid-point of the price range set forth on the cover page of this prospectus), and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

A $1.00 increase (decrease) in the assumed initial public offering price of $      per share would increase (decrease) the net proceeds to us from this offering by approximately $      million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Similarly, a one million share increase (decrease) in the number of shares offered by us, as set forth on the cover of this prospectus, would increase (decrease) the net proceeds to us by $      , assuming the assumed initial public offering price of $      per share (the mid-point of the price range set forth on the cover of this prospectus), remains the same, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

The principal purposes of this offering are to obtain additional capital to support our operations, to create a public market for our common stock and to facilitate our future access to the public equity markets. We anticipate that we will use the net proceeds of this offering for the following purposes:

We may also use a portion of the remaining net proceeds to in-license, acquire, or invest in complementary businesses, technologies, products or assets. However we have no current commitments or obligations to do so.

The amount and timing of our actual expenditures will depend upon numerous factors, including the ongoing status and results of SUPPRESS. Furthermore, we anticipate that we will need to secure additional funding for the further development of CMX001 for other indications, and for the development of any of our other product candidates.

Our expected use of net proceeds from this offering represents our current intentions based upon our present plans and business condition. As of the date of this prospectus, we cannot predict with certainty all of the particular uses for the net proceeds to be received upon the completion of this offering, or the amounts that we will actually spend on the uses set forth above. The amounts and timing of our actual use of the net proceeds will vary depending on numerous factors, including our ability to obtain additional financing, the relative success and cost of our research, preclinical and clinical development programs, the amount and timing of additional revenues, if any, received from our collaboration and licensing agreement with Merck, whether we are able to enter into future licensing arrangements, and whether we are able to extend our agreement with BARDA. As a result, our management will have broad discretion in the application of the net proceeds, and investors will be relying on our judgment regarding the application of the net proceeds of this offering. In addition, we might decide to postpone or not pursue clinical trials or preclinical activities (including SUPPRESS) if the net proceeds from this offering and the other sources of cash are less than expected.

Pending their use, we plan to invest the net proceeds from this offering in short- and intermediate-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or guaranteed obligations of the U.S. government.

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DIVIDEND POLICY

We have never declared or paid any cash dividends on our capital stock. We currently intend to retain all available funds and any future earnings to support our operations and finance the growth and development of our business. We do not intend to pay cash dividends on our common stock for the foreseeable future. Any future determination related to our dividend policy will be made at the discretion of our board of directors and will depend upon, among other factors, our results of operations, financial condition, capital requirements, contractual restrictions, business prospects and other factors our board of directors may deem relevant.

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CAPITALIZATION

The following table sets forth our cash and cash equivalents, and our capitalization as of December 31, 2012:

The pro forma information below is illustrative only and our capitalization following the closing of this offering will be adjusted based on the actual initial public offering price and other terms of this offering determined at pricing. You should read this table together with “Selected Financial Data” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our financial statements and the related notes appearing elsewhere in this prospectus.

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		As of December 31, 2012
		Actual				Pro Forma				Pro Forma As Adjusted(1)
						(unaudited)
		(in thousands, except per share amounts)
Cash and cash equivalents		$	19,906				19,906			$
Redeemable convertible preferred stock:
Redeemable convertible preferred stock warrant liability		$	7,512			$	—			$
Redeemable convertible preferred stock; $0.001 par value: 69,679,299 shares authorized, 51,404,514 shares issued and outstanding, actual; no shares authorized, issued or outstanding, pro forma; no shares authorized, issued or outstanding, pro forma as adjusted			107,723				—
Stockholders’ deficit:
Preferred stock, $0.001 par value; no shares authorized, no shares issued and outstanding actual; 10,000,000 shares authorized, no shares issued and outstanding, pro forma and pro forma as adjusted			—				—
Common stock, $0.001 par value; 89,700,000 shares authorized, 1,533,995 shares issued and outstanding, actual; 200,000,000 shares authorized, 16,955,584 shares issued and outstanding, pro forma; 200,000,000 shares authorized,        shares issued and outstanding, pro forma as adjusted			3				17
Additional paid-in capital			—				115,221
Accumulated other comprehensive loss			(2	)			(2	)
Accumulated deficit			(101,032	)			(101,032	)
Total stockholders’ equity (deficit)			(101,031	)			14,204
Total capitalization		$	14,204			$	14,204			$

The number of common shares shown as issued and outstanding on a pro forma as adjusted basis in the table is based on the number of shares of our common stock outstanding as of December 31, 2012, and excludes:

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DILUTION

If you invest in our common stock in this offering, your ownership interest will be immediately diluted to the extent of the difference between the initial public offering price per share of our common stock and the pro forma net tangible book value per share of our common stock after this offering.

Our historical net tangible book value (deficit) as of December 31, 2012, was approximately $(101.0) million, or $(65.86) per share of our common stock. Our historical net tangible book value (deficit) is the amount of our total tangible assets less our liabilities and convertible preferred stock which is not included within equity. Net historical tangible book value (deficit) per share is our historical net tangible book value (deficit) divided by the number of shares of common stock outstanding as of December 31, 2012.

Our pro forma net tangible book value (deficit) as of December 31, 2012, was $      million, or $      per share of common stock. Pro forma net tangible book value (deficit) gives effect to the conversion of all of our outstanding convertible preferred stock as of December 31, 2012, into an aggregate of 14,480,088 shares of our common stock and the reclassification of our preferred stock warrant liability into permanent equity, both of which will occur automatically upon the closing of this offering, and the issuance of 1,076,002 shares of common stock underlying shares of our Series F preferred stock issuable immediately prior to the closing of this offering in respect of the accumulated dividends on our Series F preferred stock through the date immediately preceding the date of this prospectus (based on an assumed prospectus date of April 10, 2013).

Pro forma as adjusted net tangible book value is our pro forma net tangible book value (deficit), plus the effect of the sale of        shares of our common stock in this offering at an assumed initial public offering price of $      per share (the mid-point of the range set forth on the cover of this prospectus), and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us. This amount represents an immediate increase in pro forma as adjusted net tangible book value of $      per share to our existing stockholders, and an immediate dilution of $      per share to new investors participating in this offering.

The following table illustrates this dilution on a per share basis:

Assumed initial public offering price per share						$
Historical net tangible book value (deficit) per share as of December 31, 2012		$	(65.86	)
Pro forma increase in net tangible book value per share as of December 31, 2012 attributable to the conversion of convertible preferred stock			6.97
Pro forma increase in net tangible book value per share as of December 31, 2012 attributable to the issuance of 1,076,002 shares of common stock underlying shares of our Series F preferred stock issuable immediately prior to the closing of this offering in respect of the accumulated dividends on our Series F preferred stock through the date immediately preceding the date of this prospectus (based on an assumed prospectus date of April 10, 2013)			7.26
Increase in pro forma net tangible book value per share attributable to new investors participating in this offering
Pro forma as adjusted net tangible book value per share after this offering
Dilution per share to new investors participating in this offering						$

A $1.00 increase (decrease) in the assumed initial public offering price of $      per share (the mid-point of the price range set forth on the cover page of this prospectus) would increase (decrease) the pro forma as adjusted net tangible book value (deficit) per share after this offering by approximately $      per share and the dilution in pro forma per share to investors participating in this offering by approximately $      per share, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Similarly, a one million share increase (decrease) in the number of shares offered by us, as set forth on the cover of this prospectus, would increase (decrease) the pro forma as adjusted net tangible book value

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(deficit) per share after this offering by approximately $      and the dilution in pro forma per share to investors participating in this offering by approximately $      , assuming the assumed initial public offering price of $      per share (the mid-point of the price range set forth on the cover of this prospectus) remains the same, and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

If the underwriters exercise their over-allotment option in full to purchase        additional shares of our common stock in this offering, the pro forma as adjusted net tangible book value will increase to $      per share, representing an immediate increase in pro forma as adjusted net tangible book value (deficit) to existing stockholders of $      per share and an immediate dilution of $      per share to new investors participating in this offering.

The following table summarizes, on a pro forma as adjusted basis as of December 31, 2012, the number of shares purchased or to be purchased from us, the total consideration paid or to be paid to us, and the average price per share paid or to be paid to us by existing stockholders and new investors participating in this offering at an assumed initial public offering price of $      per share (the mid-point of the range set forth on the cover of this prospectus), before deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. As the table below shows, new investors participating in this offering will pay an average price per share substantially higher than our existing stockholders paid.

		Total Shares								Total Consideration								Average Price Per Share
		Number				Percent				Amount				Percent
		(in thousands, except percents and per share data)
Existing stockholders before this offering							%			$					%			$
Investors participating in this offering
Total							100	%		$					100	%

A $1.00 increase (decrease) in the assumed initial public offering price of $    per share (the mid-point of the price range set forth on the cover page of this prospectus) would increase (decrease) the total consideration paid by new investors, total consideration paid by all stockholders and the average price per share paid by all stockholders by approximately $      , $      and $      , respectively, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Similarly, a one million share increase (decrease) in the number of shares offered by us, as set forth on the cover of this prospectus, would increase (decrease) the total consideration paid by new investors, total consideration paid by all stockholders and the average price per share paid by all stockholders by approximately $      , $      and $      , respectively, assuming the assumed initial public offering price of $      per share (the mid-point of the price range set forth on the cover of this prospectus) remains the same, and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

If the underwriters exercise their over-allotment option in full to purchase        additional shares of our common stock in this offering, the number of shares of common stock held by existing stockholders will be reduced to        , or      % of the total number of shares of common stock to be outstanding after this offering, and the number of shares of common stock held by investors participating in this offering will be further increased to      , or      % of the total number of shares of common stock to be outstanding after this offering.

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The foregoing discussion and tables are based on 17,090,085 shares of common stock outstanding as of December 31, 2012, after giving effect to the conversion of our outstanding convertible preferred stock as of December 31, 2012, into an aggregate of 14,480,088 shares of common stock, and the issuance of 1,076,002 shares of common stock underlying shares of our Series F preferred stock issuable immediately prior to the closing of this offering in respect of the accumulated dividends on our Series F preferred stock through the date immediately preceding the date of this prospectus (based on an assumed prospectus date of April 10, 2013), and excludes:

Effective immediately upon the execution and delivery of the underwriting agreement for this offering, an aggregate of 1,408,450 shares of our common stock will be reserved for issuance under the 2013 plan (plus 427,829 shares of common stock reserved for issuance under our 2012 plan as of December 31, 2012, which shares will be added to the shares reserved under the 2013 plan upon its effectiveness). Furthermore, we may choose to raise additional capital through the sale of equity or convertible debt securities due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent we issue additional shares of common stock or other equity or convertible debt securities in the future, there will be further dilution to investors participating in this offering.

Entities affiliated with certain of our existing stockholders and directors have indicated an interest in purchasing up to an aggregate of approximately $     million in shares of our common stock in this offering at the initial public offering price. However, because indications of interest are not binding agreements or commitments to purchase, the underwriters could determine to sell more, less or no shares to any of these potential investors and any of these potential investors could determine to purchase more, less or no shares in this offering. The foregoing discussion and tables do not reflect any potential purchases by these potential investors.

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SELECTED FINANCIAL DATA

The following selected financial data should be read together with our financial statements and related notes and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” appearing elsewhere in this prospectus. The selected financial data in this section are not intended to replace our financial statements and the related notes. Our historical results are not necessarily indicative of the results that may be expected in the future and results of interim periods are not necessarily indicative of the results for the entire year.

The selected statement of operations data for the years ended December 31, 2010, 2011 and 2012 and the selected balance sheet data as of December 31, 2011 and 2012 are derived from our audited financial statements appearing elsewhere in this prospectus. The pro forma basic and diluted net loss per common share data are computed using the weighted-average number of shares of common stock outstanding, after giving effect to the conversion (using the as if-converted method) of all shares of our convertible preferred stock into common stock and the issuance of 1,076,002 shares of common stock underlying shares of our Series F preferred stock issuable immediately prior to the closing of this offering in respect of the accumulated dividends on our Series F preferred stock through the date immediately preceding the date of this prospectus (based on an assumed prospectus date of April 10, 2013).

		Years Ended December 31,
		2010				2011				2012
		(in thousands, except share and per share data)
Statement of Operations:
Revenues:
Collaboration and licensing revenues		$	—			$	55			$	17,445
Contract and grant revenues			1,715				12,046				16,275
Total revenues			1,715				12,101				33,720
Operating expenses:
Research and development			19,413				27,695				27,821
General and administrative			7,606				9,398				8,682
Total operating expenses			27,019				37,093				36,503
Loss from operations			(25,304	)			(24,992	)			(2,783	)
Other (expense) income:
Interest expense			(154	)			(212	)			(776	)
Fair value adjustments to warrant liability			—				(385	)			(847	)
Other income			1				—				—
Net loss			(25,457	)			(25,589	)			(4,406	)
Accretion of redeemable convertible preferred stock			—				(9,565	)			(4,357	)
Net loss attributable to common shareholders		$	(25,457	)		$	(35,154	)		$	(8,763	)
Net loss per share, basic and diluted		$	(17.52	)		$	(23.49	)		$	(5.75	)
Weighted-average shares outstanding:
Basic and diluted			1,453				1,496				1,525
Pro forma net loss per share basic and diluted (unaudited):
Weighted-average pro forma shares outstanding, basic and diluted (unaudited):

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		As of December 31,
		2011				2012
		(in thousands, except share and per share data)
Balance Sheet Data:
Cash and cash equivalents		$	13,607			$	19,906
Short-term investments, available-for-sale			5,918				9,849
Working capital			18,010				23,931
Total assets			25,432				32,031
Loan payable(1)			2,601				14,620
Redeemable convertible preferred stock warrant liability			6,491				7,512
Redeemable convertible preferred stock			103,366				107,723
Accumulated deficit			(93,681	)			(101,035	)
Total stockholders’ deficit			(93,680	)			(101,031	)

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MANAGEMENT’S DISCUSSION AND ANALYSIS
OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

The following discussion and analysis should be read in conjunction with “Selected Financial Data” and our financial statements and related notes included elsewhere in this prospectus. This discussion and analysis and other parts of this prospectus contain forward-looking statements based upon current beliefs, plans and expectations that involve risks, uncertainties and assumptions, such as statements regarding our plans, objectives, expectations, intentions and projections. Our actual results and the timing of selected events could differ materially from those anticipated in these forward-looking statements as a result of several factors, including those set forth under “Risk Factors” and elsewhere in this prospectus. You should carefully read the “Risk Factors” section of this prospectus to gain an understanding of the important factors that could cause actual results to differ materially from our forward-looking statements. Please also see the section entitled “Special Note Regarding Forward-Looking Statements.”

Overview

Chimerix is a biopharmaceutical company committed to the discovery, development and commercialization of novel, oral antiviral therapeutics that are designed to transform patient care in areas of high unmet medical need. Our proprietary lipid technology has given rise to two clinical-stage compounds, CMX001 and CMX157, which have demonstrated the potential for enhanced antiviral activity and safety in convenient, orally administered dosing regimens. We have worldwide rights to our lead product candidate, CMX001, and anticipate beginning the Phase 3 SUPPRESS study in 2013 for the prevention of CMV infection in HSCT recipients. We intend to develop CMX001 as the first broad-spectrum antiviral against dsDNA viruses. Our second clinical-stage compound, CMX157, is a Phase 1 product candidate for the treatment of HIV and was licensed to Merck, Sharp & Dohme Corp. (Merck) in 2012.

To date, we have devoted substantially all of our resources to our research and development efforts relating to our product candidates, including conducting clinical trials with our product candidates, providing general and administrative support for these operations and protecting our intellectual property. We do not have any products approved for sale and have not generated any revenue from product sales. From our inception through December 31, 2012, we have funded our operations primarily through:

We have incurred net losses in each year since our inception in 2000. Our net losses were approximately $25.5 million, $25.6 million, and $4.4 million for the years ended December 31, 2010, 2011 and 2012, respectively. As of December 31, 2012, we had an accumulated deficit of approximately $101.0 million. Substantially all our net losses resulted from costs incurred in connection with our research and development programs and from general and administrative costs associated with our operations.

We expect to continue to incur significant expenses and increasing operating losses for at least the next several years. We anticipate that our expenses will increase substantially as we:

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We do not expect to generate revenue from product sales unless and until we successfully complete development and obtain marketing approval for one or more of our product candidates, which we expect will take a number of years and is subject to significant uncertainty. Accordingly, we anticipate that we will need to raise additional capital in addition to the net proceeds of this offering prior to the commercialization of CMX001 or any of our other product candidates. Until such time that we can generate substantial revenue from product sales, if ever, we expect to finance our operating activities through a combination of equity offerings, debt financings, government or other third-party funding, marketing and distribution arrangements and other collaborations, strategic alliances and licensing arrangements. However, we may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all, which would have a negative impact on our financial condition and could force us to delay, limit, reduce or terminate our research and development programs or commercialization efforts. Failure to receive additional funding could cause us to cease operations, in part or in full.

Financial Overview

Revenue

To date, we have not generated any revenue from product sales. All of our revenue to date has been derived from government grants and contracts and the receipt of up-front proceeds under our collaboration and license agreement with Merck.

In September 2003, we were awarded a $36.3 million grant from the National Institute of Allergy and Infectious Diseases (NIAID) to support our development of an oral drug for the treatment of smallpox. The work performed under this grant resulted in our selection of CMX001 as a lead product candidate for development. The grant, and our activities conducted in connection therewith, were substantially complete in early 2010. However, the grant was not formally terminated until February 2011.

In February 2011, we entered into a contract with Biomedical Advanced Research and Development Authority (BARDA), a U.S. governmental agency that supports the advanced research and development, manufacturing, acquisition, and stockpiling of medical countermeasures. The contract consists of an initial performance period, referred to as the base performance segment, which ends on May 31, 2013, plus up to four extension periods of around one year each, referred to as option segments, each of which may be exercised at BARDA’s sole discretion. The contract is a cost plus fixed fee development contract. Under the contract as currently in effect, if each follow-on option segment is exercised by BARDA, we may receive up to $75.8 million in expense reimbursement and $5.3 million in fees. We are currently completing the base performance segment of the contract under which we may receive up to a total of approximately $31.0 million. As of December 31, 2012, we had recognized revenue in aggregate of $28.3 million with respect to the base performance segment.

In July 2012, we entered into a collaboration and license agreement granting Merck exclusive worldwide rights to CMX157, our oral nucleotide compound currently being evaluated to treat HIV infection. Under the terms of the agreement, Merck receives an exclusive worldwide license for any human use of CMX157 and is responsible for future development and commercialization of CMX157. Following execution of the agreement, we received a $17.5 million upfront payment. In addition, we are eligible to receive payments up to

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$151.0 million upon the achievement of certain development and regulatory milestones, as well as tiered royalties on net sales escalating from high single digit to low double digits based on the volume of sales. Such royalties continue through the later of expiration of our patent rights or ten years from the first commercial sale on a country-by-country basis.

In the future, we may generate revenue from a combination of product sales, license fees, milestone payments and royalties from the sales of products developed under licenses of our intellectual property. We expect that any revenue we generate will fluctuate from quarter to quarter as a result of the timing and amount of license fees, milestone and other payments, and the amount and timing of payments that we receive upon the sale of our products, to the extent any are successfully commercialized. If we fail to complete the development of our product candidates in a timely manner or obtain regulatory approval for them, our ability to generate future revenue, and our results of operations and financial position, would be materially adversely affected.

Research and Development Expenses

Since our inception, we have focused our resources on our research and development activities, including conducting preclinical studies and clinical trials, manufacturing development efforts and activities related to regulatory filings for our product candidates. We recognize research and development expenses as they are incurred. Our research and development expenses consist primarily of:

From our inception through December 31, 2012, we have incurred approximately $123.2 million in research and development expenses, of which we estimate $92.3 million relates to our development of CMX001. In the years ended December 31, 2010, 2011 and 2012, we spent $19.4 million, $27.7 million, and $27.8 million, respectively, on research and development expenses. We plan to increase our research and development expenses for the foreseeable future as we continue the development of CMX001 for the prevention of CMV infection in HSCT and other indications and to further advance the development of our other product candidates, subject to the availability of additional funding. Our direct research and development expenses consist principally of external costs, such as fees paid to investigators, consultants, central laboratories and CROs, in connection with our clinical trials, and costs related to acquiring and manufacturing clinical trial materials. We typically use our employee and infrastructure resources across multiple research and development programs.

The successful development of our clinical and preclinical product candidates is highly uncertain. At this time, we cannot reasonably estimate the nature, timing or costs of the efforts that will be necessary to complete the remainder of the development of any of our clinical or preclinical product candidates or the period, if any, in which material net cash inflows from these product candidates may commence. This is due to the numerous risks and uncertainties associated with the development of our product candidates, including:

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A change in the outcome of any of these variables with respect to the development of a product candidate could mean a significant change in the costs and timing associated with the development of that product candidate. For example, if the FDA or another regulatory authority were to require us to conduct clinical trials beyond those that we currently anticipate will be required for the completion of clinical development of a product candidate, or if we experience significant delays in enrollment in any of our clinical trials, we could be required to expend significant additional financial resources and time with respect to the development of that product candidate.

CMX001

The majority of our research and development resources are currently focused on our Phase 3 clinical trial for CMX001, SUPPRESS, and our other planned clinical and preclinical studies and other work needed to submit CMX001 for regulatory approval in the United States and Canada. We have incurred and expect to continue to incur significant expense in connection with these efforts, including expenses related to:

In addition, pursuant to our contract with BARDA, we are evaluating CMX001 for the treatment of smallpox. During the base performance segment of the contract, we incurred significant expense in connection with the development of orthopox virus animal models, the demonstration of efficacy and pharmacokinetics of CMX001 in the animal models, the conduct of an open label clinical safety study for subjects with dsDNA infections, and the manufacture and process validation of bulk drug substance and 100 mg tablets.

General and Administrative Expenses

General and administrative expenses consist primarily of salaries and related costs for employees in executive, finance, corporate development and human resources and administrative support functions, including stock-based compensation expenses and benefits. Other significant general and administrative expenses include accounting and legal services, expenses associated with obtaining and maintaining patents, cost of various consultants, occupancy costs and information systems.

We expect that our general and administrative expenses will increase as we operate as a public company and due to the potential commercialization of our product candidates. We believe that these increases will likely include increased costs for director and officer liability insurance, costs related to the hiring of additional personnel and increased fees for outside consultants, lawyers and accountants. We also expect to incur increased costs to comply with corporate governance, internal controls, investor relations and disclosures, and similar requirements applicable to public companies.

Interest Income (Expense), Net

Interest income consists of interest earned on our cash, cash equivalents and short-term investments. We expect our interest income to increase following the completion of this offering as we invest the net proceeds from this offering pending their use in our operations.

Interest expense pertains primarily of interest accrued or paid on amounts outstanding under our loan and security agreement with SVB and MidCap.

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Critical Accounting Policies and Estimates

Our management’s discussion and analysis of our financial condition and results of operations is based on our financial statements, which we have prepared in accordance with generally accepted accounting principles in the United States (GAAP). The preparation of our financial statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of our financial statements, as well as the reported revenues and expenses during the reported periods. We evaluate these estimates and judgments on an ongoing basis. We base our estimates on historical experience and on various other factors that we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions.

While our significant accounting policies are more fully described in Note 2 to our financial statements appearing elsewhere in this prospectus, we believe that the following accounting policies related to revenue recognition, clinical trial expenses, valuation of stock-based compensation and restricted stock units are the most critical for fully understanding and evaluating our financial condition and results of operations.

Revenue Recognition

We derive our revenues from two sources: contracts and grants, and collaborations and licensing. Contract and grant revenues are revenues generated pursuant to federal contracts and other awarded grants. Collaboration and licensing revenues are revenues related to license and collaboration agreements. We recognize revenue in accordance with the criteria outlined in the SEC’s Topic 13 and Accounting Standards Codification (ASC) 605-25 and by the Financial Accounting Standards Board (FASB). Following these accounting pronouncements, revenue is recognized when all four of the following criteria are met: (i) persuasive evidence of an arrangement exists; (ii) delivery of the products and/or services has occurred and risk of loss has passed; (iii) the selling price is fixed or determinable; and (iv) collectability is reasonably assured.

For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively.

Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of our substantive performance obligations. If we do not have substantive performance obligations, we recognize non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment, and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation.

Milestone payments are recognized when earned, provided that (i) the milestone event is substantive, (ii) there is no ongoing performance obligation related to the achievement of the milestone earned, and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement and the related risk associated with the achievement of the milestone. Contingent based event payments we may receive under a license or collaboration agreement will be recognized when received.

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From our inception through December 31, 2012, we have not generated any revenue from product sales. For the same period, we have generated $65.7 million in grant and contract revenue. We recognize revenue under government grants and contracts as qualifying research activities are conducted based on invoices received from company vendors. Any amounts received in advance of performance are recorded as deferred revenue until earned.

We entered into a collaboration and license agreement with Merck in July 2012. The agreement provides for various types of payments, including a $17.5 million non-refundable upfront license fee, contingent event-based milestone payments and future royalties on net product sales. We recognized the upfront license fee payment from Merck as revenue for the year ended December 31, 2012, as our remaining performance obligations under the contract are not considered substantive. The contingent event-based payments pursuant to our agreement with Merck do not meet the definition of a milestone as achievement of the triggering event for such payments is based on the performance of Merck and not our performance. Therefore the milestone method will not be applied to any such payments.

Clinical Trial Accruals

As part of the process of preparing financial statements, we are required to estimate our expenses resulting from our obligation under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to us under such contracts. Our clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.

Our objective is to reflect the appropriate clinical trial expenses in our financial statements by matching those expenses with the period in which services and efforts are expended. We account for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. We determine accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of trials, or the services completed. During the course of a clinical trial, we adjust the rate of clinical trial expense recognition if actual results differ from the estimates. We make estimates of our accrued expenses as of each balance sheet date in our financial statements based on facts and circumstances known at that time. Although we do not expect that our estimates will be materially different from amounts actually incurred, our understanding of status and timing of services performed relative to the actual status and timing of services performed may vary and may result in us reporting amounts that are too high or too low for any particular period. Through December 31, 2012, there had been no material adjustments to our prior period estimates of accrued expenses for clinical trials. However, due to the nature of estimates, we cannot assure you that we will not make changes to our estimates in the future as we become aware of additional information about the status or conduct of our clinical trials.

Valuation of Stock-Based Compensation

We record the fair value of stock options issued to employees as of the grant date as compensation expense. We recognize compensation expense over the requisite service period, which is equal to the vesting period. For non-employees, we also record the fair value of stock options as of the grant date as compensation expense. We then periodically re-measure the awards to reflect the current fair value at each reporting period until the non-employee completes the performance obligation or the date on which a performance commitment is reached. Expense is recognized over the related service period.

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Stock-based compensation expense includes stock options granted to employees and non-employees and has been reported in our statements of operations as follows:

		Years Ended December 31,
		2010				2011				2012
		(in thousands)
Research and development
Employee		$	299			$	315			$	336
Non-employee			—				—				80
General and administrative
Employee			454				651				921
Non-employee			—				—				59
Total		$	753			$	966			$	1,396

We calculate the fair value of stock-based compensation awards using the Black-Scholes option-pricing model. The Black-Scholes option-pricing model requires the use of subjective assumptions, including volatility of our common stock, the expected term of our stock options, the risk free interest rate for a period that approximates the expected term of our stock options and the fair value of the underlying common stock on the date of grant. In applying these assumptions, we considered the following factors:

The assumptions used in the Black-Scholes option-pricing model for the years ended December 31, 2010, 2011, and 2012 are set forth below:

Employee Stock Options

		Years Ended December 31,
		2010				2011				2012
Volatility			91.00%				82.00%				80.55%
Expected term (in years)			7.0				7.0				6.0
Risk-free interest rate			2.69%				2.85%				0.86%
Expected dividend yield			0%				0%				0%
Weighted-average option value per share		$	1.75			$	1.74			$	1.93

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Non-employee Stock Options

		Years Ended December 31,
		2010				2011				2012
Volatility			—				77.80%				81.77%
Expected term (in years)			—				2.7				5.8
Risk-free interest rate			—				0.40%				0.78%
Expected dividend yield			—				0%				0%
Weighted-average option value per share			—			$	3.38			$	3.48

Common Stock Fair Value

The fair value of our common stock for purposes of determining the exercise price for stock option grants was determined on each grant date by our board of directors, or by a committee of our board of directors acting under delegated authority, with input from management. All options to purchase shares of our common stock were intended to be granted with an exercise price per share no less than the fair value per share of our common stock underlying those options on the date of grant, determined in good faith and based on the information known to us on the date of grant. In the absence of a public trading market for our common stock, on each grant date, our board of directors, or a committee of our board of directors acting under delegated authority, considered various objective and subjective factors, along with input from management, to determine the fair value of our common stock, including:

Our board of directors, or a committee of our board of directors acting under delegated authority, also considered and relied upon appraisals of the value of our stock from an independent third-party valuation specialist who conducted a thorough analysis using methodologies, approaches and assumptions consistent with the American Institute of Certified Public Accountants (AICPA) Audit and Accounting Practice Aid Series: Valuation of Privately Held Company Equity Securities Issued as Compensation (AICPA Practice Guide). The independent third-party valuation specialist provided appraisals containing the valuation analyses described below as to the fair value of our common stock as of June 1, 2009, February 15, 2011, December 31, 2011, September 30, 2012, December 31, 2012 and March 1, 2013.

The June 1, 2009 Valuation

The valuation analysis as of June 1, 2009, identified three primary components of our business: CMX001 for the smallpox indication, CMX001 for commercial indications, and CMX157 for HIV and other assets.

The valuation of CMX001 for the smallpox indication involved combining a Monte Carlo simulation with an income approach that reflected the significant business risk associated with procuring government contracts and receiving the expected base revenue going forward. Separately, as part of our long-range planning, we developed expense and potential sales projections that indicated the expected growth path of research and development expenditures. This data was used as input to a compound option-pricing model which was then used to estimate values of CMX001 for commercial indications and CMX157 for HIV and other assets.

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In addition, the AICPA guidelines require the examination of the implied value of our equity when a financing occurs on or very close to the valuation date. Since our Series E preferred stock financing was expected to occur shortly following the valuation date, this was used as a basis for determining the total value of our equity following the financing event. The valuation analysis yielded a fair value of our common stock of $3.16 per share as of June 1, 2009.

Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options on the dates set forth in the table below in reliance on the valuation analysis as of June 1, 2009, and the other objective and subjective factors described above:

Grant Dates		Number of Common Shares Underlying Options Granted				Exercise Price per Common Share				Fair Value per Common Share				Intrinsic Value per Grant
January 15, 2010			41,547			$	3.16			$	3.16				—
February 5, 2010			1,492			$	3.16			$	3.16				—
April 14, 2010			234,771			$	3.16			$	3.16				—
April 20, 2010			56,338			$	3.16			$	3.16				—
May 11, 2010			7,125			$	3.16			$	3.16				—
May 24, 2010			39,436			$	3.16			$	3.16				—
July 6, 2010			39,436			$	3.16			$	3.16				—
July 20, 2010			52,672			$	3.16			$	3.16				—
August 12, 2010			14,084			$	3.16			$	3.16				—

The February 15, 2011 Valuation

AICPA guidelines require that when a financing event takes place close to the valuation date, the implied value of equity within that financing must be considered in the valuation analysis. Since our Series F preferred stock financing closed in early February 2011, this event was used as a basis for this valuation. Our value of equity was calculated by back-solving for the overall equity value implied in the financing. Our Series F preferred stock financing resulted in gross proceeds of $45.0 million, approximately 62% of which was raised from new outside investors. Because this investment was a significant amount, where a portion was made by informed investors that had no prior investment in us, we determined that this investment represented the fair value of our Series F preferred stock and the related warrants to purchase Series F preferred stock issued in connection therewith. After setting up the contingent claims allocation model to be representative of the total interests of each class of equity security then-outstanding, the model was back-solved, holding the claims of each equity security constant relative to one another, in order to determine the fair value of our equity. The valuation analysis yielded a fair value of our common stock of $2.35 per share as of February 15, 2011.

Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options to purchase our common stock on the dates set forth in the table below in reliance on the valuation analysis as of February 15, 2011, and the other objective and subjective factors described above:

Grant Dates		Number of Common Shares Underlying Options Granted				Exercise Price per Common Share				Fair Value per Common Share				Intrinsic Value per Grant
April 7, 2011			721,530			$	2.35			$	2.35				—
April 8, 2011			12,674			$	2.35			$	2.35				—
May 10, 2011			39,716			$	2.35			$	2.35				—
June 20, 2011			14,084			$	2.35			$	2.35				—
August 15, 2011			14,084			$	2.35			$	2.35				—
September 6, 2011			3,380			$	2.35			$	2.35				—
September 30, 2011			15,774			$	2.35			$	2.35				—
November 17, 2011			70,422			$	2.35			$	2.35				—
February 22, 2012(1)			1,690			$	2.35			$	2.49			$	240
February 28, 2012(1)			4,225			$	2.35			$	2.49			$	600
March 29, 2012(1)			14,084			$	2.35			$	2.49			$	2,000
April 18, 2012(1)			14,084			$	2.35			$	2.49			$	2,000

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The December 31, 2011 Valuation

The valuation analysis at December 31, 2011, was completed in two stages. Using a contingent claims model in combination with our sale of Series F preferred stock, which occurred in February 2011, the fair value of total equity and all components of our capital structure, including our common stock, was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporated both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities that are consistent with the expectations of market participants, a distribution of equity values was produced which covered the range of events that an informed market participant might expect. These outcomes were organized into ranges and a probability was calculated based on the percent of the total falling into each range. This process created a range of equity values. Using a contingent claims framework, each equity value in the array was allocated to the various components of the capital structure, including our common stock. The value of our common stock was weighted by its respective probability to determine the final fair value of our common stock as of December 31, 2011. The valuation analysis yielded a fair value of our common stock of $2.38 per share as of December 31, 2011.

Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options on the dates set forth in the table below in reliance on the valuation analysis as of December 31, 2011, and the other objective and subjective factors described above.

Grant Dates		Number of Common Shares Underlying Options Granted				Exercise Price per Common Share				Fair Value per Common Share				Intrinsic Value per Grant
May 16, 2012			1,408			$	2.38			$	3.38			$	1,400
June 1, 2012			14,084			$	2.38			$	3.38			$	14,100
June 13, 2012			123,019			$	2.38			$	3.38			$	123,000
June 27, 2012			845			$	2.38			$	3.38			$	840
July 16, 2012			14,084			$	2.38			$	3.38			$	14,000
August 17, 2012			7,041			$	2.38			$	4.26			$	13,250
September 17, 2012			2,816			$	2.38			$	4.26			$	5,300
October 8, 2012(1)			4,224			$	2.38			$	4.26			$	7,950
October 25, 2012(1)			4,507			$	2.38			$	4.26			$	8,480

The September 30, 2012 Valuation

The valuation analysis at September 30, 2012, was completed in two stages. Using a contingent claims model in combination with our sale of Series F preferred stock, which occurred in February 2011, the fair value of total equity and all components of our capital structure, including our common stock, was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities that are consistent with the expectations of market participants, a distribution of equity values was produced which covered the range of events that an informed market participant might expect. These outcomes were organized into ranges and a probability was calculated based on the percent of the total falling into each range. This process created a range of equity values.

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In addition to the range of simulation outcomes associated with the firm as a going concern, an additional outcome was assigned to reflect the increased likelihood of the occurrence of an initial public offering. As a result of an in-depth management assessment regarding developments in our business, a 20% probability of an initial public offering was assigned. In particular, during the period from December 31, 2011, through September 30, 2012, the following events occurred which increased the likelihood of the occurrence of an initial public offering:

Using a contingent claims framework, each equity value in the array was allocated to the various components of the capital structure, including our common stock. The value of our common stock was weighted by its respective probability to determine the final fair value of our common stock as of September 30, 2012. The valuation analysis yielded a fair value of our common stock of $4.26 per share as of September 30, 2012.

Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options on the date set forth in the table below subject to the completion of the valuation analysis as of September 30, 2012, and the other objective and subjective factors described above:

Grant Date		Number of Common Shares Underlying Options Granted				Exercise Price per Common Stock				Fair Value per Common Share				Intrinsic Value per Grant
November 18, 2012			176,056			$	4.26			$	4.26				—

The December 31, 2012 Valuation

The valuation analysis at December 31, 2012, was completed in two stages. Using a contingent claims model in combination with our sale of Series F preferred stock, which occurred in February 2011, the fair value of total equity and all components of our capital structure, including our common stock was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities that are consistent with the expectations of market participants, a distribution of equity values was produced which covered the range of events that an informed market participant might expect. These outcomes were organized into ranges and a probability was calculated based on the percent of the total falling into each range. This process created a range of equity values.

In addition to the range of simulation outcomes associated with the firm as a going concern, an additional outcome was assigned to reflect the increased likelihood of the occurrence of an initial public offering. As a result of an in-depth management assessment regarding the developments in our business, a 30% probability of an initial public offering was assigned. In particular, during the period from September 30, 2012, through December 31, 2012, the following events occurred which increased the likelihood of the occurrence of an initial public offering:

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Using a contingent claims framework, each equity value in the array was allocated to the various components of the capital structure, including our common stock. The value of our common stock was weighted by its respective probability to determine the final fair value of our common stock as of December 31, 2012. The valuation analysis yielded a fair value of our common stock of $5.05 per share as of December 31, 2012.

Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options on the dates set forth in the table below subject to the completion of the valuation analysis as of December 31, 2012, and the other objective and subjective factors described above:

Grant Date		Number of Common Shares Underlying Options Granted				Exercise Price per Common Stock				Fair Value per Common Share				Intrinsic Value per Grant
February 4, 2013			84,507			$	5.05			$	5.05				—
February 21, 2013			1,408			$	5.05			$	5.05				—

The March 1, 2013 Valuation

The valuation analysis at March 1, 2013, was completed in two stages. Using a contingent claims model in combination with our sale of Series F preferred stock, which occurred in February 2011, the fair value of total equity and all components of our capital structure, including our common stock was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities that are consistent with the expectations of market participants, a distribution of equity values was produced which covered the range of events that an informed market participant might expect. These outcomes were organized into ranges and a probability was calculated based on the percent of the total falling into each range. This process created a range of equity values.

In addition to the range of simulation outcomes associated with the firm as a going concern, an additional outcome was assigned to reflect the increased likelihood of the occurrence of an initial public offering. As a result of an in-depth management assessment regarding the developments in our business, a 45% probability of an initial public offering was assigned. In particular, during the period from December 31, 2012, through March 1, 2013, the following events occurred which increased the likelihood of the occurrence of an initial public offering:

Using a contingent claims framework, each equity value in the array was allocated to the various components of the capital structure, including our common stock. The value of our common stock was weighted by its respective probability to determine the final fair value of our common stock as of March 1, 2013. The valuation analysis yielded a fair value of our common stock of $7.57 per share as of March 1, 2013.

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Our board of directors, or a committee of our board of directors acting under delegated authority, granted stock options on the date set forth in the table below subject to the completion of the valuation analysis as of March 1, 2013, and the other objective and subjective factors described above:

Grant Date		Number of common shares underlying options granted				Exercise price per common share				Fair value per common share				Intrinsic value per grant
March 13, 2013			98,591			$	7.57			$	7.57				—

In connection with the preparation of the financial statements necessary for inclusion in the registration statement related to this offering, we reassessed the estimated fair value of our common stock on a retrospective basis for financial reporting purposes. Based on the September 30, 2012, and December 31, 2012, valuation reports, we concluded that certain stock options granted during 2012 had an exercise price (which was determined in good faith based on all available information as of the date of grant, rather than based on retrospective analysis) that was different than the reassessed fair value of the common stock at the date of grant. We used these fair value reassessments to determine stock-based compensation expense which is recorded in our financial statements. The difference between the reassessed fair value of the common stock versus the exercise price of the stock options is reflected as intrinsic value in the applicable tables above.

The intrinsic value of all outstanding vested and unvested options as of December 31, 2012, was as follows:

		Number of Options				Aggregate Intrinsic Value
						(in thousands)
Unvested			989,143			$	1,471
Vested			1,604,280			$	3,231

Restricted Stock Units (RSUs)

In 2012, we issued RSUs to certain employees which vest immediately upon the earlier of (i) a change of control and (ii) the effective date of a registration statement for our initial public offering, subject to the employee’s continuous service with us from the grant date through the applicable vesting event. The RSUs entitle the employee upon or shortly following vesting to receive a number of shares of common stock that is equal to the number of RSUs granted. We only record compensation expense attributable to the RSUs if it is probable that the performance criteria will be satisfied. As of December 31, 2012, there were a total of 43,199 RSUs outstanding. The grant date fair value of the RSUs was $2.49 per unit. As of December 31, 2012, no compensation has been recorded as it was not considered probable that the performance criteria will be met.

Fair Value Adjustments to Warrant Liability

We issued warrants to purchase shares of our Series F preferred stock in connection with (i) a loan and security agreement entered into with SVB and MidCap in January 2012, and (ii) an equity financing agreement with certain investors for the sale of Series F preferred stock, which occurred in February 2011. As discussed in Note 2 to our financial statements appearing elsewhere in this prospectus, the warrants to purchase shares of our Series F preferred stock are classified as a liability and are required to be measured at fair value. The adjustment to the fair valuation of the warrants resulted in other expense of $385,000 and $847,000 for the year ended December 31, 2011 and 2012, respectively. The warrants were valued using a two stage process. Using a contingent claims model, the fair value of total equity and all components of our capital structure, including the warrants, was determined as of the time of our sale of Series F preferred stock. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporated both Monte Carlo and risk neutral frameworks. Using a contingent claims framework, each equity value in the array was allocated to the various components of the capital structure including the warrants. Each warrant value was weighted by its respective probability to determine the final fair value of the warrants as of December 31, 2011 and 2012. The key unobservable inputs used in the determination of the December 31, 2012 fair value are (i) volatility – 79%, (ii) range of implied fair value of the Series F redeemable convertible preferred stock – $2.19 to $2.85, (iii) time to liquidity – 8 months to 5 years, and (iv) range of probabilities of liquidity event outcomes – 2% to 31%.

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Upon completion of this offering, these warrants will be adjusted to fair value with any changes recorded in other income (expense). The warrant liability will then be reclassified as common stock warrants. At such time, the warrant liability will also be reclassified to additional paid-in capital, and no further revaluations will be necessary.

Utilization of Net Operating Loss Carryforwards

At December 31, 2011 and 2012, we had net operating loss carryforwards for federal and state tax purposes of approximately $80.2 million and $75.9 million and $83.4 million and $65.8 million, respectively, which begin to expire in 2020 and 2018, respectively. In addition, we had tax credit carryforwards for federal tax purposes of approximately $0.9 million as of December 31, 2012, which begin to expire in 2022. The future utilization of net operating loss and tax credit carryforwards may be limited due to changes in ownership. In general, if we experience a greater than 50% point aggregate change in ownership of certain significant stockholders or groups over a three-year period (a Section 382 ownership change), utilization of our pre-change net operating loss carryforwards is subject to an annual limitation under Section 382 of the Code (and similar state laws). The annual limitation generally is determined by multiplying the value of our stock at the time of such ownership change (subject to certain adjustments) by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the pre-change net operating loss carryforwards before utilization and may be substantial. We have determined that a Section 382 ownership change occurred in 2002 and 2007 resulting in limitations of at least $64,000 and $762,000, respectively, of losses incurred prior to the respective ownership change dates. We believe that, with our initial public offering, our most recent private placement and other transactions that have occurred since 2007, we may have triggered an ownership change limitation. We may also experience ownership changes in the future as a result of subsequent shifts in our stock ownership. As a result, if we earn net taxable income, our ability to use our pre-change net operating loss carryforwards to offset United States federal taxable income may be subject to limitations, which could potentially result in increased future tax liability to us.

JOBS Act

On April 5, 2012, the JOBS Act was enacted. Section 107 of the JOBS Act provides that an “emerging growth company” can take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities Act for complying with new or revised accounting standards. In other words, an “emerging growth company” can delay the adoption of certain accounting standards until those standards would otherwise apply to private companies. We have irrevocably elected not to avail ourselves of this extended transition period and, as a result, we will adopt new or revised accounting standards on the relevant dates on which adoption of such standards is required for other public companies.

We are in the process of evaluating the benefits of relying on other exemptions and reduced reporting requirements provided by the JOBS Act. Subject to certain conditions set forth in the JOBS Act, as an “emerging growth company,” we intend to rely on certain of these exemptions, including without limitation, (i) providing an auditor’s attestation report on our system of internal controls over financial reporting pursuant to Section 404(b) of the Sarbanes-Oxley Act, and (ii) complying with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial statements, known as the auditor discussion and analysis. We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of this offering, (b) in which we have total annual gross revenue of at least $1.0 billion, or (c) in which we are deemed to be a large accelerated filer, which means the market value of our common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30th, and (2) the date on which we have issued more than $1.0 billion in non-convertible debt during the prior three-year period.

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Results of Operations

Comparison of the Years Ended December 31, 2010 and 2011

		Years Ended December 31,								Increase (Decrease)				% Increase (Decrease)
		2010				2011
		(in thousands, except percentages)
Revenues:
Collaboration and license revenue		$	—			$	55			$	55				*
Contract and grant revenue			1,715				12,046				10,331				602.4	%
Operating expenses:
Research and development			19,413				27,695				8,282				42.6	%
General and administrative			7,606				9,398				1,792				23.6	%
Loss from operations			(25,304	)			(24,992	)			312				1.2	%
Interest expense, net			(154	)			(212	)			58				37.7	%
Fair value of warrant adjustment			—				(385	)			385				*
Other income			1				—				(1	)			*
Net loss		$	(25,457	)		$	(25,589	)		$	132				0.5	%

Contract and Grant Revenue

For the year ended December 31, 2011, we recorded $12.0 million in revenue for services performed pursuant to the BARDA contract that was awarded in February 2011. In the year ended December 31, 2010, our revenue consisted of amounts paid pursuant to our grant from the NIAID and a $491,000 federal research and development tax credit.

Research and Development Expenses

Research and development expenses were $19.4 million and $27.7 million for the years ended December 31, 2010 and 2011, respectively. The increase in research and development expenses during this period of $8.3 million, or 42.6%, was primarily due to:

General and Administrative

General and administrative expenses were $7.6 million and $9.4 million for the years ended December 31, 2010 and 2011, respectively. The increase in general and administrative expenses during this period of $1.8 million, or 23.6%, was primarily due to:

Interest Expense, Net

Interest expense, net was $154,000 and $212,000 for the years ended December 31, 2010 and 2011, respectively. The increase of $58,000, or 37.7%, relates to interest expense attributable to a full year of

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interest payments made in 2011 in connection of the loan we incurred in March 2010, as compared to eight months of interest payments made in 2010.

Fair Value of Warrant Adjustment

Some of our outstanding warrants are deemed to be derivative instruments that require liability classification and mark-to-market accounting. As such, at the end of each reporting period, the fair value of the warrants were determined by us using a two-stage contingent claims model, resulting in the recognition of additional losses of $385,000 for the year ended December 31, 2011. The loss is due to the increased value of the warrants due to increased likelihood of the occurrence of a liquidity event. We did not have any warrants outstanding at December 31, 2010 that were deemed to be derivative instruments.

Comparison of the Years Ended December 31, 2011 and 2012

		Years Ended December 31,								Increase (Decrease)				% Increase (Decrease)
		2011				2012
		(in thousands, except percentages)
Revenues:
Collaboration and license revenue		$	55			$	17,445			$	17,390				316.2	%
Contract and grant revenue			12,046				16,275				4,229				35.1	%
Operating expenses:
Research and development			27,695				27,821				126				0.4	%
General and administrative			9,398				8,682				(716	)			(7.6	%)
Income (loss) from operations			(24,992	)			(2,783	)			(22,209	)			(88.9	%)
Interest expense, net			(212	)			(776	)			564				266.0	%
Fair value of warrant adjustment			(385	)			(847	)			462				120.0	%
Net loss		$	(25,589	)		$	(4,406	)		$	(21,183	)			(82.8	%)

Collaboration and License Revenue

Collaboration and license fee revenue for the year ended December 31, 2012, consisted of revenue from an upfront license payment related to our exclusive collaboration and license arrangement with Merck for the rights to CMX157. The upfront license payment was fully recognized in the quarter in which execution of a definitive agreement took place. We did not have significant collaboration and license revenue for the year ended December 31, 2011.

Contract and Grant Revenue

Contract and grant revenues for the years ended December 31, 2011 and 2012, were $12.0 million and $16.3 million, respectively, and consisted of revenue related to our BARDA contract. Revenue increased $4.2 million, or 35.1%, during the year due to the timing of our research activities and the level of services required to be performed under our BARDA contract. In the year ended December 31, 2012, we were fully engaged in conducting Chemistry, Manufacturing and Controls validation, pre-clinical testing, and program management in connection with our BARDA contract; whereas in the year ending December 31, 2011, our revenues were lower as the work performed under our BARDA contract was more “start-up” in nature and for a smaller reimbursable amount.

Research and Development Expenses

During the years ended December 31, 2011 and 2012, our research and development expenses were $27.7 million and $27.8 million, respectively, representing an increase of $126,000, or 0.4%. This increase in research and development expense primarily reflected:

The above costs were partially offset by a decrease of $530,000 in non-clinical development costs for CMX001 and an additional $186,000 decrease in clinical trial costs primarily driven by the status of our Phase 2 clinical trial for CMX001 that was completed in early 2012.

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General and Administrative Expenses

During the years ended December 31, 2011 and 2012, our general and administrative expenses were $9.4 million and $8.7 million, respectively, representing a decrease of $716,000, or 7.6%. This decrease in general and administrative expenses was due primarily to:

Interest Expense, Net

During the years ended December 31, 2011 and 2012, our interest expense, net was $212,000 and $776,000, respectively, representing an increase of $564,000. During the year ended December 31, 2012, as compared to the year ended December 31, 2011, the net interest expense increased primarily due to the addition of non-cash amortization of finance charges associated with entering into a loan and security agreement in January 2012.

Fair Value of Warrant Adjustment

Some of our outstanding warrants are deemed to be derivative instruments that require liability classification and mark-to-market accounting. As such, at the end of each reporting period, we determined the fair value of the warrants were determined using a two-stage, contingent claims model, resulting in the recognition of additional losses of $385,000 and $847,000 for the years ended December 31, 2011 and 2012, respectively. These losses are primarily due to the increased value of the warrants due to increased likelihood of the occurrence of a liquidity event.

Liquidity and Capital Resources

We have incurred losses since our inception in 2000 and as of December 31, 2012, we had an accumulated deficit of $101.0 million. We anticipate that we will continue to incur losses for at least the next several years. We expect that our research and development and general and administrative expenses will continue to increase and, as a result, we will need additional capital to fund our operations, which we may obtain through one or more of equity offerings, debt financings, government or other third-party funding, strategic alliances and licensing or collaboration arrangements.

Since our inception through December 31, 2012, we have funded our operations principally through the receipt of funds from the private placement of approximately $100.4 million of equity securities, approximately $37.4 million of research funding from our various NIAID awards and approximately $28.3 million in revenue from our BARDA contract, debt financings totaling $21.0 million, and $17.5 million of licensing revenue under our collaboration agreement with Merck. As of December 31, 2012, we had cash and cash equivalents of approximately $19.9 million. Cash in excess of immediate requirements is invested in accordance with our investment policy, primarily with a view to liquidity and capital preservation.

During 2012, we entered into a loan and security agreement with SVB and MidCap allowing for borrowings up to $15.0 million. In January 2012, we borrowed $3.0 million under this agreement which had an interest only period for twelve months, followed by a thirty month principal and interest period at a rate of 8.25%. In September 2012, we borrowed an additional $12.0 million under this agreement that had an interest only period of six months followed with a thirty-two month principal interest period at 8.25%.

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Cash Flows

		Years Ended December 31,
		2010				2011				2012
		(in thousands)
Net cash used in operating activities		$	(21,681	)		$	(26,279	)		$	(1,876	)
Net cash used in investing activities			(236	)			(6,236	)			(4,139	)
Net cash provided by financing activities			4,603				42,816				12,314
Net increase (decrease) in cash and cash equivalents		$	(17,314	)		$	10,301			$	6,299

Operating Activities

Net cash used in operating activities of $21.7 million during the year ended December 31, 2010, was primarily a result of our $25.5 million net loss, offset by net changes in our operating assets and liabilities of $2.7 million and the add-back of non-cash expenses of $753,000 for stock-based compensation, $213,000 for depreciation, and $119,000 amortization of investment discount. The net change in our operating assets and liabilities included a decrease of accounts receivable of $937,000 and $181,000 of prepaid expenses and an increase in accounts payable and accrued liabilities of $1.6 million.

Net cash used in operating activities of $26.3 million during the year ended December 31, 2011, was primarily a result of our $25.6 million net loss, offset by net changes in our operating assets and liabilities of $2.6 million and the add-back of non-cash expenses of $1.1 million for stock-based compensation, $270,000 for depreciation, $385,000 increase in assets due to revaluation of our warrant liabilities, and $117,000 in amortization of investment discount. The net change in our operating assets and liabilities included increases in accounts receivable of $4.2 million and prepaid expenses of $442,000, offset in part by an increase in accounts payable and accrued liabilities of $2.1 million.

Net cash used in operating activities of $1.9 million during the year ended December 31, 2012, was primarily the result of our net loss of $4.4 million, offset by net changes in our operating assets and liabilities of $315,000 and the add-back non-cash items of $1.4 million for stock-based compensation, $847,000 increase in assets due to revaluation of our warrant liabilities, $280,000 for depreciation, and $322,000 of amortization for fees paid in connection with our loan. The net change in our operating assets and liabilities include decreases in our accounts receivable of $3.4 million offset by increases in accounts payable and accrued liabilities of $3.8 million.

Investing Activities

Net cash used in investing activities during the periods presented primarily reflect our use of cash to purchase short-term investments, offset by sales and maturities of short-term investments.

Financing Activities

Net cash provided by financing activities in the year ended December 31, 2010, primarily consisted of approximately $4.6 million of net loan proceeds, which we received in March 2010. Net cash provided by financing activities for the year ended December 31, 2011 primarily consisted of approximately $44.8 million of net proceeds from the sale of our Series F preferred stock, offset by an approximately $2.0 million repayment of indebtedness. Net cash provided by financing activities for the year ended December 31, 2012, primarily consisted of approximately $12.4 million of net loan proceeds related to a loan agreement we entered into in January 2012.

Future Funding Requirements

To date, we have not generated any revenue from product sales. We do not know when, or if, we will generate any revenue from product sales. We do not expect to generate significant revenue from product sales unless and until we obtain regulatory approval of and commercialize CMX001 or any of our other product candidates. At the same time, we expect our expenses to increase in connection with our ongoing development activities, particularly as we continue the research, development and clinical trials of, and seek regulatory approval for, our product candidates. Upon the closing of this offering, we expect to incur additional costs associated with operating as a public company. In addition, subject to obtaining regulatory approval of any of our product candidates, we expect to incur significant commercialization expenses for product sales,

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marketing, manufacturing and distribution. We anticipate that we will need substantial additional funding in connection with our continuing operations.

Based upon our current operating plan, we believe that the net proceeds from this offering, together with our existing cash, cash equivalents and short-term investments, will enable us to fund our operating expenses and capital requirements through at least mid-2015. We intend to devote the net proceeds from this offering to fund our Phase 3 clinical trial, SUPPRESS, and any additional clinical or preclinical studies necessary to support and to submit an application for CMX001 for the prevention of CMV infection in HSCT patients. We have based our estimates on assumptions that may prove to be wrong, and we may use our available capital resources sooner than we currently expect. Because of the numerous risks and uncertainties associated with the development and commercialization of our product candidates, we are unable to estimate the amounts of increased capital outlays and operating expenditures necessary to complete the development of our product candidates.

Our future capital requirements will depend on many factors, including:

Until such time, if ever, as we can generate substantial revenue from product sales, we expect to finance our cash needs through a combination of equity offerings, debt financings, government or other third-party funding, marketing and distribution arrangements, or other collaborations, strategic alliances or licensing arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, the ownership interests of our common stockholders will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of our common

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stockholders. Debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends. If we raise additional funds through government or other third-party funding, marketing and distribution arrangements or other collaborations, strategic alliances or licensing arrangements with third parties, we may have to relinquish valuable rights to our technologies, future revenue streams, research programs or product candidates or to grant licenses on terms that may not be favorable to us.

Contractual Obligations and Commitments

The following table summarizes our contractual obligations at December 31, 2012:

		Total				Less Than 1 Year				1 – 3 Years				3 – 5 Years				More Than 5 Years
		(In thousands)
Operating leases(1)		$	187			$	169			$	18				—				—
Loan payable and interest(2)			16,873				6,042				10,831				—				—
Minimum royalties(3)		$	1,550				—				50				500				1,000
Total		$	18,610			$	6,211			$	10,899			$	500			$	1,000

In addition to the amounts set forth in the table above, we have payment obligations under license agreements that are contingent upon future events such as our achievement of specified development, regulatory and commercial milestones. Under our license agreement with UC, we made milestone and sublicense payments totaling approximately $1.2 million through December 31, 2012. We will be required to make additional payments when certain milestones are achieved and we are obligated to pay royalties based on future product sales. As of December 31, 2012, we were unable to estimate the timing or likelihood of achieving the milestones or making future product sales and, therefore, any related payments are not included in the table above. In connection with the development and commercialization of CMX001 and CMX157, in addition to royalties on product sales, we could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement. Under our license agreement with the University of Michigan, we are required to pay minimum royalties from 2016 through the expiration of the last licensed patent (which we estimate will occur in 2024) which are included in the table above, but any additional royalties that may be payable under the University of Michigan agreement are not estimable and therefore not included in the table above.

Additionally, we enter into contracts in the normal course of business with CROs for clinical trials and clinical supply manufacturing and with vendors for preclinical research studies and other services and products for operating purposes, which generally provide for termination or cancellation within 30 days of notice, and therefore are not included in the table above. We also have an employment agreement with our chief executive officer that requires the funding of specific payments, if certain events occur, such as a change in control or the termination of his employment without cause. These potential payment obligations, which are described in “Executive and Director Compensation — Potential Payments Upon Termination or Change of Control”, are not included in the table above.

Off-Balance Sheet Arrangements

During the periods presented we did not have, nor do we currently have, any off-balance sheet arrangements as defined under SEC rules.

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Recent Accounting Pronouncements

In May 2011, the FASB issued Accounting Standards Update (ASU) 2011-04, Fair Value Measurement (Topic 820): Amendments to Achieve Common Fair Value Measurements and Disclosure Requirement in U.S. GAAP and IFRS. This guidance includes amendments that clarify the intent regarding the application of existing fair value measurements and disclosures, and amendments that change a particular principle or requirement for measuring fair value or for disclosing information about fair value measurements. This guidance is effective for interim and annual periods beginning after December 15, 2011. The standard was adopted as of January 1, 2012, and the retrospective application of this standard did not have a material impact on our financial statements.

In June 2011, the FASB issued ASU 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income. This guidance requires that all non-owner changes in stockholders’ equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. This guidance is effective for interim and annual periods beginning after December 15, 2011. This standard was adopted as of January 1, 2012, and the retrospective application of this standard did not have a material impact on our financial statements.

Basic and Diluted Net Loss Attributable to Common Stockholders per Common Share

Our Series A preferred stock, Series B preferred stock, Series B-1 preferred stock, Series C preferred stock, Series D preferred stock, Series E preferred stock and Series F preferred stock represent participating securities. However, since we operate at a loss, and losses are not allocated to our preferred stock, the two class method does not affect our calculation of earnings per share. We had a net loss for all periods presented. Accordingly, the inclusion of stock options to purchase common stock and warrants exercisable for common stock would be anti-dilutive.

Dilutive common stock equivalents would include the dilutive effect of convertible securities, stock options to purchase common stock and warrants exercisable for common stock. Potentially dilutive common stock equivalents totaled approximately 6,781,550 shares, 11,034,134 and 11,259,579 shares for the years ended December 31, 2010, 2011 and 2012, respectively. Potentially dilutive common stock equivalents were excluded from the diluted earnings per share denominator for all periods because of their anti-dilutive effect. Therefore, the weighted-average shares used to calculate both basic and diluted earnings per share are the same.

Quantitative and Qualitative Disclosure About Market Risk

Our primary exposure to market risk is interest income sensitivity, which is affected by changes in the general level of U.S. interest rates. Due to the short-term duration of our investment portfolio and the low risk profile of our investments, an immediate 10.0% change in interest rates would not have a material effect on the fair market value of our portfolio. Accordingly, we would not expect our operating results or cash flows to be affected to any significant degree by the effect of a sudden change in market interest rates on our investment portfolio.

We do not believe that our cash, cash equivalents and available-for-sale investments have significant risk of default or illiquidity. While we believe our cash and cash equivalents and certificates of deposit do not contain excessive risk, we cannot provide absolute assurance that in the future our investments will not be subject to adverse changes in market value. In addition, we maintain significant amounts of cash and cash equivalents at one or more financial institutions that are in excess of federally insured limits.

Inflation generally affects us by increasing our cost of labor and clinical trial costs. We do not believe that inflation has had a material effect on our results of operations during 2011 or 2012.

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BUSINESS

Overview

Chimerix is a biopharmaceutical company committed to the discovery, development and commercialization of novel, oral antiviral therapeutics that are designed to transform patient care in areas of high unmet medical need. Our proprietary lipid technology has given rise to two clinical-stage compounds, CMX001 and CMX157, which have demonstrated the potential for enhanced antiviral activity and safety in convenient, orally administered dosing regimens. We have worldwide rights to our lead product candidate, CMX001, and anticipate beginning the Phase 3 SUPPRESS study in 2013 for the prevention of cytomegalovirus (CMV) infection in hematopoietic stem cell transplant (HSCT) recipients. We intend to develop CMX001 as the first broad-spectrum antiviral against double-stranded DNA (dsDNA) viruses. Our second clinical-stage compound, CMX157, is a Phase 1 product candidate for the treatment of HIV and was licensed to Merck, Sharp & Dohme Corp. (Merck) in 2012.

CMX001 is an orally administered drug that utilizes our proprietary lipid technology to deliver high intracellular concentrations of a potent antiviral compound, cidofovir-diphosphate (CDV-PP). Following oral dosing, CMX001 is absorbed through the gut, remains intact in the plasma, and is readily taken up by and delivered into cells. Once inside cells, CMX001 is converted into CDV-PP, which acts as an alternative substrate that interferes with the enzymes necessary for viral replication. When CDV-PP is selected by critical enzymes as a substrate over the normal cellular substrate (i.e. nucleotides), the result is diminished enzymatic activity and therefore diminished viral replication.

CMX001 is similar to the drug cidofovir in that both drugs are converted into CDV-PP once inside cells. Although cidofovir is approved for administration in an intravenous formulation, Vistide®, it requires a high plasma concentration to deliver a therapeutic level of cidofovir into cells and its use is limited due to the risk of kidney damage. In contrast, oral administration of CMX001 results in significantly lower plasma concentrations, higher levels of drug inside cells, and a lower risk of kidney toxicity.

Double-stranded DNA viral infections such as CMV are commonly transmitted in childhood and early adulthood, and generally remain latent in individuals with a functioning immune system. However, in immunocompromised patients, such as HSCT or solid organ transplant (SOT) recipients, CMV and other dsDNA viral infections are associated with significant morbidity, mortality, graft rejection and co-infection with other opportunistic infections. CMV, a human herpesvirus, is the most common infectious pathogen in HSCT, and can result in life-threatening pneumonia or other organ involvement, particularly in the first 100 days following transplant when the immune system is most vulnerable. In vitro, CMX001 has shown broad-spectrum antiviral activity against all families of dsDNA viruses that cause human disease, including herpesviruses, adenoviruses (AdV), polyomaviruses such as BK virus (BKV), papillomaviruses and orthopoxviruses.

In the HSCT setting, there are three paradigms for addressing viral infections: prevention, preemptive therapy and treatment of disease. Prevention is the administration of an antiviral to at-risk patients to avoid reactivation of a latent virus. Preemptive therapy is the initiation of antiviral(s) only after detection of a specific virus in the blood (viremia) in an asymptomatic patient. Treatment is the watch-and-wait approach of initiating antiviral therapy after the virus is detected in an organ system where clinical signs or symptoms are present.

No drugs are approved for prevention of CMV in HSCT recipients, primarily due to significant renal and hematological side effects. We believe that a safe and well-tolerated antiviral with demonstrated efficacy in prevention settings would provide a new standard of care for immunocompromised patients. In HSCT, a safe and effective therapy for CMV prevention could potentially replace the current practice of frequent monitoring for CMV viremia and initiation of anti-CMV preemptive therapy following detection. In addition, we believe that an antiviral that could reduce the frequency of other dsDNA viruses and avoid increasing the risk of other opportunistic infections could provide measureable clinical and pharmacoeconomic benefits for patients and the health care system.

Chimerix demonstrated the potential of CMX001 in a 230-patient Phase 2 dose-escalation study for the prevention of CMV reactivation in HSCT recipients. In this study, CMX001 or placebo was administered to

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HSCT recipients from stem cell engraftment through Week 13 post-transplant. A reduction of more than 50% in risk of CMV infection was observed for the subjects who received CMX001 in 100 mg doses twice weekly (BIW). Ten percent of subjects (five of 50 subjects) in the CMX001 100 mg BIW cohort met the primary endpoint, CMV disease or a positive quantitative blood test for CMV at the end of the dosing period, versus 37% of subjects (22 of 59 subjects) in the placebo cohort (p=0.002, where the p-value is the statistical probability of a result not due to chance alone). CMX001’s dose-limiting toxicity was diarrhea, which was addressed with a Safety Monitoring and Management Plan (SMMP) incorporated in the final Phase 2 cohort and in subsequent studies, and which will be implemented in SUPPRESS. There was no evidence of kidney, hematologic or bone marrow toxicity in this study.

The results of this Phase 2 study, together with CMX001’s overall preclinical and clinical profile, which includes a safety database of more than 800 subjects exposed to CMX001 in controlled and uncontrolled clinical studies, support the progression to a Phase 3 study of CMX001 for the prevention of CMV infection in high-risk HSCT recipients. Discussions with the FDA have resulted in an agreed population, endpoint and study design for which we have received a “Study May Proceed” letter. We remain in active discussions with the FDA regarding final protocol specifics and anticipate initiation of dosing in 2013. The primary endpoint is a composite endpoint of either (i) CMV disease, or (ii) initiation of anti-CMV preemptive therapy triggered by a positive test for CMV in the blood (viremia), and will be assessed through Week 24 post-transplant. We intend to enroll 540 at-risk (i.e., with latent CMV infection) HSCT recipients who will be randomized to receive one of two twice-weekly doses of CMX001 or placebo. Secondary endpoints include pharmacoeconomic data and the incidence of disease and reactivation of other herpesviruses, AdV, and BKV.

We intend to submit a new drug application (NDA) under an accelerated approval pathway seeking regulatory approval to market CMX001 in the United States and equivalent applications outside the United States. We have received Fast Track designation from the FDA for the CMV, AdV and smallpox indications for CMX001.

We believe that there is a significant commercial opportunity for an antiviral such as CMX001 with broad-spectrum activity against dsDNA viruses. According to the Center for International Blood and Marrow Transplant Research and the Organ Procurement and Transplantation Network, more than 20,000 HSCTs and 28,000 SOTs are performed annually in the United States, with similar numbers of transplants performed annually in Europe according to the European Group for Blood and Marrow Transplantation and the World Health Organization. More than 65% of stem cell transplant patients are at increased risk of CMV infection due to prior exposure to CMV (i.e., seropositive). Outside the transplant population, many factors are influencing the epidemiology of dsDNA viral infections, including the use of potent immunosuppressive therapies in autoimmune and other diseases. Since 2009, Chimerix has made CMX001 available under expanded access regulations to over 80 transplant centers worldwide for the treatment of over 430 patients with life-threatening dsDNA viral infections and no satisfactory alternative treatment options, reflecting the unmet medical need in this therapeutic area. Our CMX001 Compassionate Use Program consists of the emergency investigational new drug (EIND) program which has provided treatment to 230 individuals and Study 350, the expanded access study which enrolled 215 patients meeting similar inclusion criteria as the EINDs.

If CMX001 obtains regulatory approval, we intend to build our own sales force and to commercialize CMX001. In the United States, approximately 200 institutions perform transplants, of which approximately 75% perform HSCT and 75% perform SOT. As a result, we believe we can commercialize CMX001 for prevention of CMV in HSCT recipients in the United States and Canada with a relatively small marketing and specialty sales force infrastructure of approximately 50 employees.

We are also evaluating the potential for CMX001 as a preemptive therapy for AdV infections. In December 2012, we completed enrollment of a Phase 2 placebo-controlled study of preemptive therapy for AdV viremia in 48 pediatric and adult HSCT recipients. Data on the mortality and disease endpoints for this Phase 2 study are expected during the second half of 2013. Future clinical development for CMX001 may include a Phase 3 CMV prevention study in pediatric HSCT recipients, as well as the possible development of CMX001 for BKV infection in HSCT and SOT recipients.

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CMX157, our second clinical stage compound, is an oral nucleotide compound in Phase 1 development for the treatment of HIV infection. In July 2012, we granted Merck an exclusive worldwide license to develop and commercialize CMX157 for all human uses. Merck is responsible for all development and marketing activities for CMX157 on a worldwide basis.

Our Strategy

Our strategy is to discover, develop, and commercialize novel oral antiviral therapeutics in areas of significant unmet medical need. Key elements of our strategy include:

We may enter into additional collaborations to implement our strategy.

Our Product Candidates

The following chart depicts our product candidates, their indications, and their current stage of development:

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Advantages of CMX001

Our lead product candidate, CMX001, is a broad-spectrum antiviral anticipated to enter Phase 3 clinical development in 2013 for CMV prevention in adult HSCT recipients. Utilizing our proprietary lipid technology, this nucleotide compound is dosed orally in tablet or liquid form. CMX001’s safety and tolerability profile supports its continued investigation as a potential antiviral against multiple dsDNA viruses. The structures of cidofovir and CMX001 are graphically depicted below.

We believe CMX001 has the following advantages that support its rapid development:

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Additionally, dosing with CMX001 results in levels of CDV-PP detectable in the cells for a long period of time. This allows for less frequent dosing and a low pill burden, potentially important advantages for patients.

The graphic below demonstrates the intracellular activation and site of action of CMX001, and the intracellular and plasma concentrations of CMX001 versus cidofovir.

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Development Strategy for CMX001

In a placebo-controlled Phase 2 study in high-risk HSCT patients, CMX001 100 mg BIW was demonstrated to be superior to placebo for the prevention of CMV infection (p<0.002). There was no evidence of hematologic or bone marrow toxicity. Additionally, consistent with our preclinical data, there was no evidence of on-therapy or follow-up kidney toxicity. The dose-limiting toxicity, diarrhea, was addressed with an SMMP in the final cohort of the Phase 2 study and in subsequent studies.

We anticipate initiating SUPPRESS, our planned Phase 3 study of CMX001 for the prevention of CMV infection in CMV seropositive (R+) adults undergoing HSCT, in 2013. The primary endpoint is a composite endpoint of (i) CMV disease or (ii) the initiation of preemptive anti-CMV therapy triggered by a positive test for CMV viremia. Subjects will be randomized 2:1 to active CMX001 or placebo, will take study drug through Week 14, and will be monitored from enrollment through Week 24 post-transplant. As part of the SUPPRESS trial, we plan to put in place the SMMP that was developed during the conduct of our Phase 2 study which we believe will reduce the incidence of patient withdrawals due to diarrhea. The SMMP directs the investigators to interrupt study medication when the study subject presents with gastrointestinal symptoms possibly related to the use of CMX001. In our experience, such treatment interruptions allow the symptoms to subside, after which therapy can be resumed. We believe the following factors will also increase SUPPRESS’s probability of success:

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We intend to submit an NDA under an accelerated approval pathway seeking regulatory approval to market CMX001 for the prevention of CMV infection in HSCT recipients in the United States. We have received Fast Track designation to support our development and commercialization strategy for the prevention of CMV infection.

As part of our overall development program for CMX001, we are pursuing the development of CMX001 against other dsDNA viruses:

We believe that a well-tolerated antiviral with demonstrated efficacy in prevention would provide a new standard of care for patients with various forms of immune suppression, including HSCT and SOT recipients. Additionally, the current and future epidemiology of dsDNA viral infections, influenced by the increasingly widespread use of potent immunosuppressants, the evolution of viral resistance, and the role of childhood and adult vaccines may provide additional lifecycle opportunities for CMX001 based on its broad-spectrum antiviral activity.

Market Overview

Background on dsDNA Viruses

Viruses are among the simplest infectious agents and can replicate only inside the living cells of a host. Although it is estimated that there are millions of unique virus types, only a few thousand have been well described. Viruses are typically classified into groups based on the nature of their genetic material (e.g., single- or double-stranded DNA, or single- or double-stranded RNA).

Five families of dsDNA viruses are of particular importance as causes of human illness:

A large percentage of the world’s population has been exposed to one or more dsDNA viruses, usually limited to a mild viral syndrome during childhood or early adulthood. Viruses may remain dormant for the rest of a person’s life as long as the immune system is intact. However, clinically significant viral reactivation can occur in immunocompromised patient populations, including patients who are being treated with immune-modulating therapies following transplantation, during intensive cancer chemotherapy, or as therapy for autoimmune disorders.

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Although our initial regulatory strategies are focused on HSCT and SOT, clinical indications for a broad-spectrum antiviral in many other areas of immune suppression may provide additional opportunities.

Viral infections pose a serious threat to the health of patients who have undergone HSCT or SOT. In these settings, the patient’s immune system is intentionally destroyed or suppressed to prevent stem cell or organ rejection, putting the patient at risk for reactivation of viruses that are dormant within their bodies. This can result in serious or fatal viral-induced disease, co-infection with other opportunistic viral, bacterial or fungal infections, and damage to or loss of the graft. The growing use of potent immunosuppressive drugs has successfully reduced transplant rejection and mortality rates but has also placed patients at greater risk for viral infections and their sequelae.

In the transplant setting and based on data from our CMX001 Compassionate Use Program, three dsDNA viruses are responsible for the majority of viral infections of concern: CMV, AdV and BKV. The effect of many other dsDNA viruses, each independently having a low incidence, can collectively increase morbidity and mortality within HSCT, SOT, and other immunocompromised populations.

Background on the HSCT Market and HSCT Therapies

HSCT

Stem cell transplants replace the blood forming (hematopoietic) system in patients who have malignant, damaged or defective bone marrow, offering a potential cure or remission for many cancers and genetic disorders. HSCTs are defined by the donor of the stem cells (allogeneic and autologous transplants), the source of the stem cells (bone marrow, peripheral blood or cord blood) and the conditioning regimen used prior to the transplantation (myeloablative, reduced intensity or non-myeloablative).

Allogeneic HSCTs use cells from a family member or unrelated donor and can cure or improve outcomes in a wide variety of diseases, including leukemia, lymphoma, myeloproliferative disorders, myelodysplastic syndrome, and congenital immunodeficiencies. However, allogeneic HSCT is associated with significant morbidity and mortality due to procedure-related toxicities, infection, and graft versus host disease (GVHD, a process whereby the injected stem cells (the graft) attack the tissues in the body of the transplant patient (the host)). In general, the greater the difference in the donor and recipient’s genetic make-up, the greater the risk for GVHD and the greater the need to immunosuppress patients after their transplant. Autologous HSCTs use the patient’s own cells and can improve outcomes in neoplastic diseases and autoimmune conditions. As with allogeneic HSCT, autologous HSCT therapeutic regimens and infections contribute to morbidity and mortality.

At transplantation, the donor’s cells are infused into the body through a vein and form new cells of the bone marrow, where they begin to grow and produce new red blood cells, white blood cells and platelets during a process called engraftment. Engraftment typically occurs within the first month following transplantation. Until engraftment occurs, patients have very few white blood cells to fight infections and can easily acquire serious or life-threatening infections due to their weakened immune systems. Even after engraftment, patients are at high risk for complications during the first 100 days following their transplant, particularly if ongoing immunosuppression is necessary.

Growth of the HSCT Market

HSCT remains underutilized, with many patients referred for a transplant only when they reach an advanced stage of disease. In order to increase the number of patients who could potentially benefit from HSCT, there has been significant focus on alternative stem cells sources such as unrelated donors and umbilical cord blood stem cells. However, use of unrelated donors for stem cell results in higher risk of reactivation of dsDNA viruses such as CMV.

Overall, the number of stem cell transplants being performed in the United States has grown at approximately 4% annually since 2000. Of the allogeneic transplants, the unrelated donor subset has been growing at a higher rate than other subsets within HSCT.

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Viral Diseases Associated with HSCT

CMV in HSCT

CMV, a human herpesvirus, is the most common infectious threat in HSCT, with 80% of CMV-seropositive (R+) allogeneic transplant recipients developing detectable CMV in the blood, which is known to correlate with progression to disease and death, if untreated. Common manifestations of active CMV infection in immunosuppressed patients are pneumonia, gastrointestinal (GI) disease, hepatitis, and retinitis. In addition, because CMV itself is immunosuppressive, reactivation of the virus can predispose a patient to other opportunistic infections.

Rather than waiting for evidence of CMV disease, the most commonly accepted intervention for CMV is frequent monitoring for CMV in the blood and initiation of anti-CMV preemptive therapy with intravenous ganciclovir or valganciclovir, available antivirals with the side-effect of suppression of neutrophils and an associated increased risk for bacterial and fungal infections.

The initial indication for which we are seeking regulatory approval for CMX001 is prevention of CMV infection in recipients of allogeneic HSCT who are seropositive for CMV. To the extent that the risk-benefit ratio for CMX001 is established in SUPPRESS, particularly in prevention of clinical manifestations of other dsDNA viral infections, indications in patient populations with more moderate CMV risk estimates may be pursued. Based on a survey of recent literature, we believe that the following table reflects the risk of CMV reactivation in HSCT patients:

Risk Assessment for CMV Reactivation in HSCT

AdV in HSCT

Although AdV infection is much less frequent than CMV in HSCT, disseminated AdV has a high mortality rate of 80%, and no approved therapies for prevention, preemptive therapy or treatment. AdV is more frequent in pediatric HSCT patients who have not been as widely exposed to the many AdV subspecies as have adults. Manifestations of serious AdV infection besides AdV pneumonitis include acute hemorrhagic cystitis, liver failure, and renal damage such as nephritis or obstructive nephropathy. AdV infection is also associated with graft failure or delayed engraftment in HSCT.

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BKV in HSCT

BKV, a polyomavirus, is a dsDNA virus that can be a significant medical problem in HSCT and has no approved therapy. The virus establishes lifelong latency in the kidneys and urinary tract following primary infection. BKV rarely causes disease in healthy adults; however, in HSCT recipients with prolonged immunosuppression, BKV reactivation can lead to hemorrhagic cystitis (HC), a painful condition that often requires hospitalization for pain control or bladder irrigation. HC is associated with significant hematuria and clotting, and can result in impairment of kidney and/or bladder function. Little data on epidemiology of BKV exist in the HSCT population. Our prospective data from Study 201 found a greater than 50% incidence of BKV in urine in subjects enrolled in that trial and showed evidence of worsening renal function through a decrease in estimated glomerular filtration rate (eGFR) and an increase in serum creatinine for BKV-positive subjects randomized to placebo. These data are presented in the figures below.

Study 201: CMX001 Demonstrated Statistically Significant Dose-Related Improvement in
Renal Function (e.g., eGFR)

Mean (N) Change from Baseline in eGFR (mL/min/1.73 m²) by Visit and Dose

eGFR:  estimated glomerular filtration rate

Study 201: Subjects with BKV Demonstrated Greater Differential Change in
Serum Creatinine Between CMX001 and Placebo

BKU+ = BK viruria positive; BKU- = BK viruria negative; creatinine increase = creatinine > 120 μM/L

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Background on the SOT Market and SOT Therapies

SOT of the kidney, liver, pancreas, heart, and lung has become standard therapy for selected end-stage diseases. Although quality of life and survival rates following organ transplantation have improved greatly due to advances in surgical technique, immunosuppressive therapy, and medical management, complications such as infection and graft rejection remain major causes of morbidity and mortality following SOT. Management of viral infections after transplantation involves antiviral therapy and reduction in immunosuppressive therapy, a balancing act between controlling the infection and avoiding rejection of the new organ. More than 28,000 SOTs are performed annually in the United States, and a comparable number of procedures are performed each year in Europe.

CMV in SOT

CMV remains the most frequent opportunistic infection affecting the overall outcome of SOT, and typically reactivates during the first six months following transplantation. Furthermore, a recent study has shown that 37% of patients on Valcyte for prevention of CMV in high-risk kidney, kidney-pancreas and heart transplants developed late-onset CMV within 12 months post-transplant. In addition to directly causing morbidity and occasional mortality, CMV also influences short and long term complications that collectively contribute to reduced graft and patient survival. Prevention of CMV infection and disease in SOT is a critical step forward towards improved patient outcomes but is limited by the side effects, need for monitoring and restricted addressable population of current antivirals.

BKV in SOT

BKV infection affects 20-40% of kidney transplant recipients and can lead to BKV-associated nephropathy (BKVAN), a disease resulting in loss of the new kidney in 30-65% of affected patients. The incidence of BKVAN appears to be on the rise, related to the increased use of immunosuppressive drugs. Progression to BKVAN is generally asymptomatic. However, BKV DNA can often be detected in blood or urine for several months prior to the development of renal dysfunction, which may represent an opportunity for earlier intervention with antiviral therapy.

Background on Antiviral Therapies in Transplant Patients

Antiviral therapeutics are differentiated in general based on several characteristics, the most important of which are:

Currently available therapies have significant shortcomings with respect to many of these characteristics. In particular, existing therapies are limited by their lack of broad-spectrum efficacy as well as their major side effects, notably nephrotoxicity and myelosuppression. These limitations can lead to increased hospitalizations, severe and life-threatening neutropenia, renal impairment, use of expensive granulocyte colony-stimulating factor (G-CSF) therapies, platelet and blood transfusions, need for dialysis, and life-threatening secondary bacterial and fungal infections. The prevalence of disease and the limitations of existing therapies contribute to the significant unmet medical need for effective and better tolerated antivirals.

CMX001’s differentiated product profile has the potential to address many of these unmet medical needs. See the table titled “Key Characteristics of CMX001 and Approved and Investigational Antivirals” below.

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Unmet Medical Need in HSCT Antiviral Therapy

There are three paradigms commonly used for addressing viral infections in the transplant setting: prevention, preemptive therapy and treatment.

In order to be approved for prevention, a therapy must be generally safe and well-tolerated without toxicities that overlap with the inherent risks of the patient population. Currently available antivirals cannot be used for prevention of common dsDNA viral diseases because they have toxicities that risk the function or survival of the new graft.

Because preemptive therapy is initiated only after the level of virus in the blood reaches a threshold associated with progression to disease, limited drug toxicities may be more acceptable as disease and mortality risks are more substantial.

Prevention

Within the field of infectious diseases, prevention of disease with a safe and well-tolerated therapeutic is a preferred paradigm. There are multiple precedents for prevention in other viral indications, including the approval of valacyclovir for the prevention of transmission of herpes simplex infection based on the well-established safety profile of acyclovir and valacyclovir. In children at high risk of disease from respiratory syncytial virus (RSV), the monoclonal antibody palizumivab was approved for prevention.

In spite of trials conducted with ganciclovir for CMV prevention, ganciclovir is approved for use only as a preemptive therapy or treatment for CMV in HSCT. Ganciclovir was limited in its ability to be used as a preventive therapy by the risk of significant neutropenia, which has multiple consequences including an increased risk of invasive bacterial and fungal infections, an increased risk of late-onset CMV disease, or even loss of the graft itself. These observations have been confirmed in multiple studies, and highlight the need for a safe and well-tolerated antiviral for use as a prevention in HSCT.

Preemptive Therapy — The Current Standard of Care in HSCT

Rather than waiting for evidence of CMV disease, the most commonly accepted intervention for CMV involves frequent monitoring for CMV viremia and initiation of anti-CMV preemptive therapy upon detection. Approximately 30-40% of HSCT recipients require preemptive therapy in response to CMV viremia, making this the most commonly used strategy to prevent the development of CMV disease in HSCT recipients. The most commonly utilized preemptive therapy is ganciclovir, which is administered intravenously and requires close monitoring for hematologic and other toxicities. Valganciclovir is an orally administered prodrug of ganciclovir with a similar toxicity profile. Second-line therapies of foscarnet or intravenous cidofovir have recognized renal toxicity. As noted above, ganciclovir initiated as preemptive therapy demonstrated a decrease in CMV disease, but is limited in overall benefit by neutropenia and resulting susceptibility to secondary invasive bacterial and fungal infections, as well as the emergence of CMV resistance.

Treatment

CMV treatment after the onset of clinical signs and symptoms has a limited impact on mortality and is no longer considered the standard of care.

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The Potential for a Broad-Spectrum Antiviral

The prevention of CMV with CMX001 provides us the opportunity to simultaneously explore the prevention and control of other dsDNA viral infections in the transplant setting. Although each of these additional viral infections has a lower incidence than does CMV in HSCT or SOT, individually and in aggregate they have a meaningful impact on clinical endpoints and healthcare utilization.

We believe prevention of reactivation of CMV and other dsDNA viruses represents a significant unmet medical need. In addition to AdV, BKV and CMV, other human herpesviruses such as EBV, herpes simplex virus types 1 and 2 (HSV-1, HSV-2), varicella-zoster virus (VZV), and human herpes virus type 6 (HHV-6) contribute to the overall morbidity and mortality in HSCT. For example, EBV has long been recognized as the most common causative agent of post-transplant lymphoproliferative disorder, a condition which is especially prevalent in the pediatric population and in certain SOT populations. Over the past several years, an increasing number of clinical syndromes, including those with neurological disease and pulmonary involvement, have been attributed to EBV infection. The increase in frequency of EBV infections has been linked to several risk factors, particularly the use of cord blood and T-cell depleted grafts.

The risks and clinical presentation of specific dsDNA viruses have been reviewed for the HSCT and SOT patient populations, but for an individual patient, multiple dsDNA viruses contribute to the risk of disease, dependent on prior exposure and current level of immunosuppression. We believe that an ideal antiviral in the transplant setting would have broad-spectrum potential to prevent CMV and other viral infections, particularly AdV and BKV as there are no approved therapies for these two viral infections.

The Competitive Landscape

Currently Available Antiviral Therapies

We believe that a well-tolerated antiviral with demonstrated efficacy as prevention would provide a new standard of care for immunocompromised patients. In HSCT, an effective CMV prevention could potentially replace the current practice of frequent monitoring for CMV viremia and initiation of CMV-specific preemptive therapy. In addition, an antiviral for CMV prevention that could reduce the frequency of other opportunistic viral infections would provide an additional measureable clinical and pharmacoeconomic benefit for patients.

To date, the safety and tolerability limitations of current therapies have precluded their use as prevention in the HSCT patient population.

Because of the importance of CMV as a pathogen in HSCT recipients, a number of companies have pursued clinical studies to assess the effectiveness of antiviral agents administered as prevention. Randomized clinical studies examining the potential of ganciclovir for CMV prevention demonstrated a significant reduction in early CMV disease, but no survival benefit due to the increased occurrence of invasive fungal and bacterial infections and late onset CMV disease. Twenty-one percent of patients had severe neutropenia with a lowest value of less than 500 cells/μL for at least two consecutive days. In this study, neutropenia was associated with an increase in infections and was a negative predictor of overall and event-free survival. Ganciclovir has also been associated with delayed engraftment and specifically a decrease in lymphocytes which protect against viral infections.

Valganciclovir (marketed as Valcyte®), an oral prodrug for delivery of ganciclovir, is approved for CMV prevention for many high-risk recipients of SOT. Sufficient risk-benefit ratios for use of valganciclovir as prevention have been demonstrated in SOT for high-risk adult and pediatric kidney and heart transplant patients, and for high-risk adult kidney-pancreas transplant patients. However, the known impact of valganciclovir on white blood cells requires frequent monitoring for evidence of asymptomatic neutropenia and related risk of invasive bacterial and fungal infections. Given the need for continued monitoring for adverse effects with current antivirals, a significant need exists for an antiviral for CMV prevention with superior safety, tolerability and resistance profiles.

Second-line Therapies: Cidofovir and Foscarnet

Administration of intravenous cidofovir (marketed as Vistide®) has become standard in some transplant centers for renal transplant patients with BKVAN, despite the limitations of the efficacy and safety profile. Anecdotal reports have claimed clearance of BKV from both the blood and allograft of renal transplant

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recipients treated with intravenous cidofovir combined with reduction in immunosuppression. However, other retrospective analyses have failed to demonstrate antiviral benefit from cidofovir therapy for BKV infection. The high potential for cidofovir to cause nephrotoxicity in patients who are already experiencing renal insufficiency remains a serious concern for treating physicians. Foscarnet is associated with significant renal toxicity, which limits its utility to patients who have ganciclovir resistance or treatment failure.

In the Phase 2 study of CMX001 for CMV prevention, preemptive therapy with ganciclovir or valganciclovir was necessary in 32% of subjects (74 of 230), primarily subjects who received either an inactive dose of CMX001 or placebo. Data available for 71 subjects demonstrate the clinical limitations and pharmacoeconomic implications of preemptive therapy:

We believe that there is an unmet medical need for safe and effective antiviral therapies to replace current preemptive therapies in order to improve outcomes and decrease transplant-related costs.

Investigational Agents for CMV

Several companies are pursuing the development of new therapies for CMV disease.

Letermovir

Letermovir is a viral terminase inhibitor with specific activity for CMV that is being developed as an oral antiviral for the prevention and treatment of CMV. AiCuris GmbH & Co. KG (AiCuris), which licensed letermovir to Merck in 2012, completed a Phase 2 study for CMV prevention in 2012 in which letermovir was tested in HSCT recipients with a limited number of underlying diseases. Based on publicly available information, mismatched or cord blood transplant recipients, and those with GVHD or with impaired liver or renal function, were excluded from the study.

Publicly presented data from letermovir’s Phase 2 study showed a benefit of letermovir versus placebo in preventing CMV reactivation during therapy, but do not address the post-therapy follow-up period. While no clinical data on letermovir resistance have been published or presented to date, resistance to letermovir was generated in vitro after a single passage.

Maribavir

Maribavir is an oral antiviral that inhibits CMV protein kinase UL97, thereby preventing viral encapsulation for CMV specifically. ViroPharma Incorporated (ViroPharma) previously discontinued development of maribavir after Phase 3 studies failed to show benefit in HSCT and liver transplant recipients for the prevention of CMV infection versus placebo and oral ganciclovir, respectively. ViroPharma is now evaluating maribavir in Phase 2 studies for the treatment of refractory CMV infection in transplant recipients using doses of 400, 800 and 1,200 mg twice daily, doses that are significantly higher than those tested in their previous Phase 3 studies. CMV resistance against maribavir has been described and published.

TransVax

TransVax is being developed by Vical Incorporated (Vical) and Astellas Pharma US, Inc. (Astellas) for the prevention of CMV disease reactivation in transplant patients. This DNA vaccine is specifically targeted at

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enhancing immunity against CMV by using CMV antigens. TransVax is currently entering Phase 3 development for the HSCT population and Phase 2 development for the SOT population. Although the publicly available Phase 2 data indicate that the vaccine prevented CMV infection in 69% of the subjects who received active vaccine versus 38% of the subjects randomized to placebo, this positive effect did not reach statistical significance in the Phase 2 study.

Key Characteristics of CMX001

Key characteristics of CMX001 along with comparative data for five approved therapies, two investigational antivirals, and one DNA-based vaccine specific for prevention of CMV in the transplant setting are presented below. Of the five therapies that are currently approved for human use, none is approved for the prevention of CMV infection in HSCT recipients.

Based on publicly available information, the table below highlights the key differentiating characteristics for CMX001, in particular the potent and broad-spectrum activity of CMX001 compared with the CMV-specific activity of a majority of other antivirals.

Key Characteristics of CMX001 and Approved and Investigational Antivirals

Preclinical and Clinical Development for CMX001

Building on positive data from our Phase 2 study for the prevention of CMV disease in HSCT recipients, we anticipate beginning our Phase 3 study, SUPPRESS, in 2013.

Preclinical Program for CMX001

In Vitro Efficacy and Resistance Data

CMX001’s broad-spectrum potency against dsDNA viruses has been characterized in vitro in cell culture systems and in vivo in multiple animal models. In cell culture assays, CMX001 is typically 50- to 100-fold more potent than cidofovir against dsDNA viruses, including herpesviruses, adenoviruses, polyomaviruses, papillomaviruses, and orthopoxviruses.

The following table shows the concentrations of CMX001 and each of the approved and investigational antivirals required to reduce viral replication by 50% in vitro. Smaller numbers depict a more potent molecule than larger numbers, and results depicted by “>” in general are above a threshold that would indicate antiviral activity (i.e., adequate in vitro data do not exist to support pursuing a clinical indication). Data are compiled from multiple sources and include multiple materials and methodologies; comparisons should be limited to general trends in orders of magnitude differences in in vitro potency.

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Broad Spectrum Activity of CMX001 versus Approved and Investigational Antivirals (EC₅₀ in μM)

Although CMX001 delivers the same active antiviral, CDV-PP, as intravenous cidofovir, the ability of CMX001 to deliver CDV intracellularly through the lipid-conjugate technology results in CMX001 demonstrating approximately 800-fold improvement in vitro in activity against BKV, more than 400-fold more activity against CMV, 65-fold more activity against AdV and 250-fold more activity against variola major, the causative agent of smallpox.

CMX001 has a high barrier to viral resistance, and no resistance-associated mutations were detected in Study 201. In vitro CMX001-resistant CMV is slow to emerge, involves a unique mutation, and has reduced fitness compared to wild-type CMV. We have completed a 39-week chronic toxicology study in monkeys and 26-additional studies in mice, rabbits, rats, dogs, and monkeys. Based on results from these studies, we do not currently plan to conduct additional toxicology studies. We have also completed 41 Absorption, Distribution, Metabolism and Excretion (ADME) studies which demonstrate that CMX001 is readily absorbed and widely distributed after oral administration in animals. In vitro cytochrome P450 and drug transporter inhibition studies indicated low-to-moderate potential for drug-drug interactions. In the development of Vistide®, Gilead identified mammary rat tumors that led to the inclusion of potential carcinogenicity in a black box warning. We observed similar findings with CMX001 and may have a black box warning for CMX001.

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Clinical Development Program for CMX001

We are developing CMX001 initially for the prevention and preemptive therapy of clinically significant infection and disease, including as a potential therapy for CMV and AdV infection and as a possible countermeasure for smallpox. To date, over 800 subjects have received CMX001 in controlled and uncontrolled studies and under EIND regulations in the United States and foreign equivalent regulations outside the United States.

Our planned CMX001 clinical program to date has been comprised of the following studies:

Based on our End-of-Phase 2 meeting and subsequent feedback from FDA, we intend to conduct SUPPRESS, our Phase 3 study which will evaluate CMX001 for the prevention of CMV infection in adult HSCT recipients. Assuming a positive outcome, the study may be sufficient for accelerated approval of CMX001. The protocol for the SUPPRESS trial has been submitted to the FDA under a CMV-specific IND held by us. We do not intend to request a Special Protocol Assessment from the FDA prior to commencing the SUPPRESS trial. Following the FDA’s 30-day safety review after the submission of the SUPPRESS protocol, we received a “Study May Proceed” letter from the FDA with respect to SUPPRESS, as well as a Fast Track designation for the CMV prevention indication.

Future clinical development for CMX001 may include a Phase 3 CMV prevention study in pediatric HSCT recipients as well as the possible development of CMX001 for BKV infection in HSCT and SOT recipients. We are also evaluating potential development activities in Europe and other key markets.

We currently hold multiple individual INDs with respect to CMX001, including an IND for the treatment of AdV infection (submitted on November 18, 2010) and an IND for the prevention of clinically significant CMV infection in HSCT patients (submitted on January 22, 2013).

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Study 201: Prevention of CMV Infection in HSCT Recipients

The key efficacy findings from our development program to date include the demonstration of superiority of CMX001 over placebo for the prevention of CMV in HSCT recipients in Study 201.

Study 201 was a randomized, placebo-controlled, dose-escalation study in CMV seropositive (R+) allogeneic HSCT recipients, evaluating the ability of CMX001 to prevent CMV infection. Subjects in five dosing groups received either placebo or oral CMX001, in doses ranging from 40 mg once weekly to 200 mg BIW. The primary endpoint was defined as (i) the incidence of CMV disease at any time during therapy, or (ii) a CMV polymerase chain reaction (PCR) assay result of greater than 200 copies/mL at the time of the last dose of study drug. All subjects who received at least one dose of drug or placebo and had at least one efficacy evaluation post baseline were included in the primary analysis, regardless of their CMV PCR status (negative or positive) at baseline (modified intent to treat, or mITT, population).

All CMX001 doses and dose regimens in Study 201 demonstrated antiviral activity when compared to placebo, with the exception of the lowest dose, 40 mg QW. The proportion of subjects who developed CMV disease or a CMV PCR positive result at the end of 100 mg BIW dosing period was 10% (five of 50 subjects) versus 37% (22 of 59 subjects) for placebo-treated subjects (p=0.002, mITT population).

In a pre-specified subgroup analysis of subjects who were CMV negative at baseline, zero of 41 subjects (0%) in the CMX001 100 mg BIW group developed CMV PCR of 1,000 copies/mL or more during the CMX001 dosing period, compared to 15 of 47 (32%) of subjects in the placebo cohort (p<0.001) (see figures below). When individual subject data were examined (CMV PCR copies/mL over time), the CMX001 100 mg BIW dose regimen resulted in lower frequency and/or lower overall levels of CMV PCR.

Study 201: CMV PCR for Individual Subjects Over Time

* Represents the clinically relevant threshold.

Subjects CMV negative at Baseline.

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Percentage of Subjects in Study 201 with CMV PCR of 1,000 Copies per mL or Greater

Overall Safety and Tolerability for CMX001

In Study 201, CMX001 100 mg BIW and CMX001 200 mg QW were sufficiently well-tolerated to warrant further evaluation. Overall, there was a similar frequency and severity of adverse events seen in these dosing groups compared to the placebo group. Regardless of dose and dosing frequency, there was no indication of myelotoxicity or nephrotoxicity associated with CMX001 or discontinuations from the study related to these events.

Because of the severity of their underlying illnesses and the multiple drugs administered to HSCT patients both pre- and post-transplant, there is a high background level of AEs in this patient population. Of the AEs reported in Study 201 in 20% or more of subjects, GI-associated events (including diarrhea, nausea, vomiting and abdominal pain) and elevated ALT levels generally increased in frequency with increasing doses of CMX001.

At a dose of CMX001 200 mg BIW, increased GI AEs were reported, particularly diarrhea. Diarrhea in the transplant setting has the potential to originate from a variety of sources, including conditioning regimens, concomitant medications, and infections. At this time, the FDA requested that doses of CMX001 be limited to a total weekly dose of 200 mg or less. As part of the FDA’s request, we implemented a program-wide SMMP that included interruption of study drug for subjects who experienced Grade 3 or higher GI AEs. In our Phase 2 study at a dose of CMX001 100 mg BIW, 10% of the subjects discontinued CMX001 due to GI AEs, compared to 3% in the placebo group. A decrease in serum albumin from baseline provided an additional marker for discriminating drug-related diarrhea from diarrhea of other etiologies. We believe that monitoring of serum albumin concentrations coupled with dose interruption is an appropriate strategy to decrease the severity of GI AEs without loss of antiviral activity and could allow for completion of the intended therapy duration. Following the introduction of the SMMP in our ongoing clinical studies, less than 10% of subjects have discontinued from CMX001 due to GI AEs. The SMMP will be included in the Phase 3 SUPPRESS study.

A dose-related, transient increase in ALT was associated with CMX001 therapy. At a dose of 100 mg BIW, approximately 30% of subjects experienced ALT increases greater than three times the upper limit of normal, compared to 16% in the placebo group. When present, the ALT increases follow a predictable pattern and return to baseline levels following completion of therapy. The CMX001-related increases in ALT were not

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associated with increases in aspartate aminotransferase or bilirubin. Few clinical hepatobiliary AEs were reported in association with CMX001 therapy and most were mild or moderate in intensity. The ALT increases observed in Study 201 were consistent with ALT elevations observed across all preclinical species exposed to CMX001, a finding considered non-adverse as there was no histopathologic evidence of liver injury or hepatic necrosis.

There has been no evidence of nephrotoxicity with CMX001 pre-clinically. The mechanism of nephrotoxicity for intravenous cidofovir is directly related to high plasma concentrations of intravenous cidofovir needed to reach therapeutic intracellular levels of CDV-PP. Cidofovir is rapidly taken up by cells in the kidney by a receptor called the human organic anion transporter one (hOAT-1), which leads to high concentrations of cidofovir in the duct system in the kidneys and subsequent renal toxicity. CMX001 is not a substrate for hOAT-1.

The lack of nephrotoxicity observed with CMX001 in preclinical in vitro and animal studies is supported by clinical data. Based on the pharmacokinetic and safety data generated in our Compassionate Use Program, the FDA granted a waiver for the conduct of a renal insufficiency clinical pharmacology study. A further indication of CMX001’s lack of nephrotoxicity was observed in Study 201, where there was a dose-related improvement in estimated GFR in the patients infected with BKV and receiving CMX001 as compared with subjects on placebo. These data provide a clinical correlate to the in vitro activity of CMX001 against BKV.

Study 202: Preemptive Therapy for AdV in HSCT Recipients

In June 2011, we initiated Study 202, a randomized, placebo-controlled, multi-site study evaluating CMX001 as a preemptive therapy for AdV disease in HSCT recipients. Although AdV infection is much less frequent than CMV in HSCT, disseminated AdV has a high mortality rate of 80%. The incidence of AdV viremia in HSCT is poorly documented but is estimated at 5 – 7% during the first 100 days post-transplant based on screening data from Study 202. Evaluation of CMX001 as a prevention for AdV would require a study size of thousands of patients, an unrealistic goal given the number of at-risk pediatric HSCTs performed annually in the United States. As such, we are evaluating the safety, tolerability and efficacy of QW and BIW regimens of CMX001 versus placebo for the preemptive management of asymptomatic AdV viremia in 48 pediatric and adult HSCT recipients at 29 transplant centers in the United States. We completed enrollment of the 48 planned subjects in December 2012. Data from Study 202 are expected in the second half of 2013.

Study 202 participants were randomized to receive 12 weeks of preemptive therapy with CMX001 or placebo, followed by a four-week post-therapy follow-up period. Adults or children weighing 50 kg or greater receive CMX001 tablets at doses of 100 mg BIW or 200 mg QW. Pediatric subjects (i.e., patients weighing less than 50 kg) receive CMX001 as a liquid formulation at doses of 2 mg/kg BIW or 4 mg/kg QW. The total dose in pediatric patients does not exceed 200 mg weekly.

The primary endpoint in Study 202 is treatment failure, a composite endpoint consisting of (i) progression to probable or definitive AdV disease, or (ii) increasing AdV viremia during randomized therapy that requires discontinuation from randomized therapy. Participants who are assessed as failures at any time during the randomized therapy phase of the study are offered open-label treatment with CMX001.

We are also evaluating multiple secondary endpoints, including incidence and time to mortality, the percentage of subjects on randomized therapy with undetectable plasma AdV PCR measured at various time points, and the percentage of subjects who have emergence or progression of CMV, EBV or BKV viremia or disease during therapy.

Open-Label Studies

Since 2009, Chimerix has made CMX001 available to over 80 transplant centers worldwide through our Compassionate Use Program, including EINDs or foreign equivalents and our formal open-label expanded access study, Study 350. Through these programs, we made CMX001 available to treat life-threatening dsDNA viral diseases in patients who had exhausted all available therapeutics or for whom there were no therapeutic options. While the majority of patients treated were HSCT or SOT recipients, we also provided CMX001 for patients with other diseases, including congenital deficiencies or HIV.

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EINDs

Clinical testing of therapeutic agents prior to approval must be performed pursuant to an IND submitted to and approved by the FDA. In addition, the FDA may allow non-approved drugs to be administered to patients in certain situations utilizing a set of regulations known as expanded access. One such type of expanded access is the EIND application. A physician may request use of an investigational antiviral product through a single-patient EIND application if:

Since 2009, when the first EIND was granted for CMX001, over 230 patients have been treated with CMX001 under EINDs or foreign equivalent regulations for severe, life-threatening dsDNA viral infections. Viruses treated with CMX001 include all major dsDNA viruses, including CMV, AdV, BKV, EBV, JCV, HHV-6, HHV-8, HSV-1, HSV-2, VZV, HPV, moscullum, and vaccinia. The average period of dosing with CMX001 was approximately 11 weeks. Over 80 international transplant centers have requested CMX001. In this EIND population, approximately one-third of patients infected with CMV were infected with at least one other dsDNA virus, the most common being BKV and AdV.

In 2010, we focused our Compassionate Use Program efforts on Study 350 and significantly curtailed the availability of CMX001 under the EIND program in an effort to standardize the data collected from patients receiving CMX001 under the expanded access regulations.

Study 350

Study 350, a multicenter, open-label clinical study of CMX001, evaluated the safety, tolerability and antiviral activity of CMX001 in 142 adult and 68 pediatric patients with various severe, life-threatening dsDNA viral infections at 36 transplant centers in the United States. Patients must have failed all other available treatment options in order to qualify for this study. Patient ages ranged from one to 78 years, and were treated for dsDNA viral infections including CMV, HSV, EBV, AdV, BKV, JCV, and HHV6. Approximately 28% of patients were co-infected with two or more dsDNA viruses. The average period of dosing in Study 350 was approximately two months. Safety data has not revealed any unidentified safety signals associated with CMX001 administration in a complex and highly compromised patient population. Data from Study 350 are under analysis and expected in 2013.

In summary, across our Compassionate Use Program, approximately one-third of patients dosed with CMX001 were co-infected with two or more dsDNA viruses.

Phase 3 Study: SUPPRESS

Our Phase 3 study, SUPPRESS, will be a placebo-controlled study in CMV seropositive (R+) adults undergoing HSCT, evaluating the safety and efficacy of CMX001 to prevent CMV infection. Subjects will be randomized to receive one of two twice-weekly doses of CMX001 (i.e., 75 mg BIW or 100 mg BIW) or placebo. The primary endpoint for SUPPRESS will be the development of clinically significant CMV infection, defined as either:

Based on data from Study 201, we estimate that at least 30% of patients in populations similar to the intended SUPPRESS population will require initiation of CMV-specific preemptive therapy. SUPPRESS will be powered to detect a 50% difference between the cohort randomized to receive placebo and either cohort randomized to CMX001. We hope to show that either of the two doses of CMX001 in SUPPRESS result in a clinically meaningful and statistically significant reduction in the risk of needing preemptive therapy, thus avoiding the morbidity, mortality and costs associated with these therapies.

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We plan to conduct SUPPRESS at 30 to 40 transplant centers in the United States and enroll 540 patients who have undergone HSCT and who have prior exposure to CMV. Inclusion and exclusion criteria will be similar to Study 201, including high risk HSCT patients. Dosing of CMX001 or placebo will begin in the early post-transplant period and will continue through Week 14 post-transplant. Subjects will be monitored weekly for CMV viremia from enrollment through Week 14 post-transplant, and then every three weeks until Week 24 post-transplant.

As part of SUPPRESS, we plan to evaluate multiple secondary endpoints, including treatment-emergent resistance, incidence of non-CMV dsDNA viruses and comparison of pharmacoeconomic and health-related qualify of life outcome parameters between CMX001- and placebo-treated subjects.

Phase 2 Data Using SUPPRESS Endpoint and Inclusion Criteria

In order to assure adequate power for the Phase 3 SUPPRESS trial, we calculated the maximum estimated failure rates for subjects enrolled in Study 201 using the primary endpoint and inclusion criteria for SUPPRESS. This analysis includes subjects with negative or positive CMV PCR at baseline (first day of dosing) and excludes subjects who had any samples during screening that were CMV PCR positive. Using a conservative approach, failures included (i) subjects with CMV disease, (ii) subjects with CMV PCR values greater than 1,000 copies/mL, (iii) subjects with CMV PCR values greater than 100 copies/mL and defined as “high risk” in the SUPPRESS protocol or (iv) subjects that initiated anti-CMV preemptive therapy, independent of CMV PCR. Where insufficient data were available, subjects were considered as having met criteria for a “failure.”

CMX001: Phase 2 Data Based on SUPPRESS Primary Endpoint and Inclusion Criteria

This analysis demonstrates that a 50% reduction (22% vs. 46%) in clinical risk, which is the assumed clinically relevant difference between CMX001 and placebo, would be achieved if similar prescriptions of subjects reach the failure endpoint in Study 301 as were observed in Study 201.

Based on completed and planned studies, we anticipate that more than 950 adult subjects will have been exposed to at least one dose of CMX001 through the end of SUPPRESS in both controlled and uncontrolled studies, including nearly 600 adult subjects enrolled in randomized, placebo-controlled studies. Of these, over 500 subjects will have received doses of at least 150 mg per week for at least 10 weeks in controlled studies upon our anticipated submission for CMX001 for the prevention of CMV in HSCT recipients.

Based on our interactions with the FDA, we believe, but cannot guarantee, that with the successful completion of SUPPRESS, we will have completed the preclinical and clinical studies necessary to submit an NDA for the prevention of CMV in HSCT recipients. We intend to submit an NDA under an accelerated

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approval pathway seeking regulatory approval to market CMX001 in the United States. If CMX001 receives accelerated approval, it may be necessary for us to conduct a post-approval Phase 3 study in order to receive full approval of CMX001.

We have received Fast Track designation from the FDA for the CMV, AdV, and smallpox indications of CMX001.

Additionally, we plan to seek regulatory approval for marketing of CMX001 for the prevention of CMV in HSCT recipients in Canada and key European markets.

Future clinical development for CMX001 may include a Phase 3 CMV prevention study in pediatric HSCT recipients (Study 311) as well as the possible development of CMX001 for BKV infection in HSCT and SOT recipients.

CMX001 as a Medical Countermeasure Against Smallpox

Variola virus, the dsDNA virus that causes smallpox, is an orthopoxvirus that infects only humans. The Department of Homeland Security (DHS) has declared smallpox to be a material threat to national security and the U.S. Centers for Disease Control and Prevention classifies smallpox as a Category A bioterror agent. Additionally, smallpox has been identified as a high-priority threat by the Public Health Emergency Medical Countermeasure Enterprise (PHEMCE). An antiviral is needed, in particular, for patients who cannot be vaccinated due to conditions that prevent them from mounting an appropriate immune response to a smallpox vaccine.

We received our initial funding for the development of CMX001 as a medical countermeasure for the treatment of smallpox from the NIAID. CMX001 demonstrated high potency in inhibiting variola virus replication in cultured cells as well as related viruses that have been used to create animal models of smallpox including ectromelia in mice, rabbitpox, monkeypox and vaccinia.

In order to supply CMX001 to the Strategic National Stockpile as a treatment for smallpox infection, FDA approval is ultimately required. We submitted an IND for CMX001 for the treatment of smallpox to FDA in 2005. The CMX001 development program for this indication was granted Fast Track Status at that time. Should we be successful with our development efforts, an NDA will be submitted to the FDA in order to obtain an approval for CMX001 for the treatment of smallpox.

Since smallpox is no longer a communicable disease in humans, the development of CMX001 for treatment of smallpox is occurring under the “Animal Efficacy Rule”. Under this Rule, the FDA can rely on the evidence from animal studies to provide substantial evidence of the effectiveness of these products in support of an NDA. Products evaluated for effectiveness under the “Animal Efficacy Rule” are evaluated for safety in clinical trials using the same regulations as exist for other drugs. Therefore, the safety data generated for CMX001 in the clinical trials described in the section titled “Clinical Development Program for CMX001” would provide the clinical safety data for the treatment of smallpox indication.

In February 2011, we were awarded a Broad Agency Announcement (BAA) contract by BARDA to fund development of CMX001 for the treatment of smallpox in the event of a smallpox outbreak. See “— Commercial Agreements” below for more information on this contract.

Under the base performance segment of the BARDA contract described below, we have devoted a substantial amount of effort to develop animal models of smallpox and to explore efficacy in these models. Additionally, as part of progressing the clinical development of CMX001 for the smallpox indication, the base performance segment of the BARDA contract supported Clinical Study CMX001-350. This study provided safety data for CMX001 relevant to the treatment of smallpox indication.

In December 2011, we presented a summary of studies of CMX001 conducted in mouse, rabbit and monkey models of smallpox and the current animal efficacy development plan to a Smallpox Advisory Committee convened by FDA to provide guidance on acceptable models of smallpox. Based on the information provided at that meeting, FDA provided specific guidance to Chimerix on the development of CMX001 for smallpox under the Animal Efficacy Rule. The FDA provided feedback on the animal models that could be used for studies that may lead to approval for a smallpox treatment indication. Specifically, the FDA suggested the mouse ectromelia model and the rabbit rabbitpox model would be appropriate for

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CMX001. In addition, we and the FDA agreed that no additional work would be conducted in the currently available monkey models of smallpox. An updated animal efficacy development plan incorporating this feedback was submitted to the FDA in August 2012 in advance of a Type C meeting in September 2012.

CMX001 has shown encouraging activity in relevant animal models of smallpox. In vivo, the antiviral activity of CMX001 has been characterized in an animal model of smallpox. In this model, a dose of CMX001 was identified that provided protection against mortality from an otherwise lethal viral inoculum.

The base performance segment of the BARDA contract has been extended from the initial targeted completion date on several occasions most recently to extend the completion date from March 31, 2013 until May 31, 2013. We will be presenting the results of our work during this base performance segment to a BARDA review committee, and subject to the outcome of this meeting, we anticipate renegotiating certain aspects of the smallpox animal plan to take into account recent guidance from the FDA for the development of CMX001 under the Animal Efficacy Rule. However, the results of this negotiation are uncertain and we do not anticipate continuing this program without ongoing support from BARDA.

CMX157

CMX157, our second oral nucleotide compound, uses the same proprietary lipid technology as CMX001 to deliver high intracellular concentrations of another potent antiviral drug, tenofovir. CMX157 is being developed for the treatment of HIV infection, and was licensed to Merck in July 2012. We submitted an IND for CMX157 for the treatment of HIV infection on April 30, 2009. We are no longer the sponsor of record for this IND. Merck became the sponsor of this IND upon its licensing of CMX157 from us.

CMX157 is a novel lipid-conjugate of the acyclic nucleoside phosphonate, tenofovir, the active molecule underlying the prodrug Viread®. Viread, which is marketed in the United States by Gilead Sciences, Inc. (Gilead), is the most widely used nucleotide reverse transcriptase inhibitor (NRTI), approved for the treatment of HIV and chronic hepatitis. Based on supportive preclinical data, we believe CMX157 has the potential for higher intracellular concentrations in target tissues of tenofovir-diphosphate (TFV-PP), the active form of both CMX157 and Viread®, as well as a decreased frequency of dosing and an improved safety profile over existing NRTIs. CMX157 is more than 200-fold more potent in vitro versus tenofovir against all major HIV subtypes resistant to current therapies, which may allow activity against tenofovir-resistant viruses and against Hepatitis B. CMX157's structure results in decreased circulating levels of tenofovir, lowering systemic exposure and thereby reducing the potential for renal side effects.

Prior to the transaction with Merck, we completed a Phase 1 clinical study of CMX157 in healthy subjects, demonstrating a favorable safety, tolerability and drug distribution profile. This study demonstrated plasma concentrations of CMX157 that exceeded target levels at doses of 100 mg and higher after a single dose. TFV-PP was measurable in peripheral blood mononuclear cells in all subjects after a single dose of 400 mg of CMX157, but not so after a standard dose of Viread. TFV-PP remained detectable for up to six days after dosing, suggesting the possibility for infrequent dosing. In the study, CMX157 was well-tolerated and no safety issues were observed. No trends in clinical laboratory results, vital signs or electrocardiogram parameters were noted, and no severe adverse events were reported. The chart below presents peak plasma concentrations after oral administration of CMX157 in the Phase 1 study.

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Plasma Concentrations After Oral Administration of CMX157

*Concentration that equaled TFV-PP level produced by TFV peak concentration in vitro.

Chimerix Chemical Library

The Chimerix Chemical Library contains over 10,000 heterocyclic ring systems and nucleosides that were originally synthesized in the laboratory of Dr. Leroy Townsend at the University of Michigan. We are currently screening the library for activity against more than thirty viruses including flaviviruses, influenza, herpesviruses and polyomaviruses. Lead chemical series have been identified for influenza and novel compounds with promising activity are being evaluated. Screening has also been completed for antifungals and a lead chemical series has been identified with broad-spectrum antifungal activity. We believe that several compounds active against key pathogens are amenable to enhancement using our proprietary lipid technology.

Commercial Agreements

Merck

In July 2012, we entered into a collaboration and license agreement granting Merck exclusive worldwide rights to CMX157, our novel lipid acyclic nucleoside phosphonate currently being evaluated to treat HIV infection. Under the terms of the agreement, Merck received an exclusive worldwide license for any human use of CMX157 and has agreed to use commercially reasonable efforts to develop and commercialize CMX157 in the United States and at least three major European markets. Following execution of the agreement, we received a $17.5 million upfront payment from Merck.

As additional consideration, we are eligible to receive up to a total of $151.0 million in milestone payments if certain development and regulatory milestones are achieved by Merck for products utilizing CMX157, as well as tiered royalties on net sales ranging from high single digits to low double digits, depending upon the volume of sales of each applicable product, if CMX157 is successfully commercialized. Milestone payments are triggered upon the completion of various stages of the regulatory approval process for each of the first two indications for CMX157, with the final milestones reached upon approval in the United States and three major European markets. Royalties for any given product will continue on a country-by-country basis through the later of the expiration of our patent rights applicable to such product or ten years from the first commercial sale of such product. As of December 31, 2012, other than the upfront payment received upon execution of the agreement, we have not received any payments from Merck pursuant to the agreement.

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Unless earlier terminated, the agreement continues in effect until the termination of Merck’s royalty payment obligations. The agreement allows for termination by Merck in its entirety, or on a region-by-region basis, upon 90 days advance written notice, or, with respect to a particular product, immediately upon written notice if Merck has a safety concern regarding such product. In addition, either party may terminate for the other party’s material breach of the agreement which remains uncured for 90 days. In the event of termination by us for material breach by Merck or termination by Merck upon written notice to us (other than termination due to safety concerns with respect to a particular product), Merck would be required to assign to us certain clinical data and regulatory materials related to CMX157 and, upon written request, grant to us a limited, non-exclusive license to Merck’s patent rights covering CMX157. In such event, we would be required to pay to Merck a tiered, low single digit royalty on net sales depending on any such product’s development stage at the time of such termination.

BARDA

In February 2011, we entered into a contract with BARDA for the advanced development of CMX001 as a medical countermeasure in the event of a smallpox release (Contract Number HHSO100201100013C). BARDA is a division of the U.S. Department of Health and Human Services (HHS) in the Office of the Assistant Secretary for Preparedness and Response that supports the advanced research and development, manufacturing, acquisition and stockpiling of medical countermeasures. The scope of work for the contract includes preclinical, clinical and manufacturing development activities that fall into the following areas: non-clinical animal efficacy studies; clinical activities; manufacturing activities; and all associated regulatory, quality assurance, management, and administrative activities. The contract has been amended several times, most recently on February 21, 2013 to extend the base performance segment through May 31, 2013.

Under the contract, BARDA will reimburse our costs, plus pay us a fixed fee, for the research and development of CMX001 as a treatment of smallpox infections. The contract consists of an initial performance period, referred to as the base performance segment, plus up to four extension periods of around one year each, referred to as option segments, each of which may be exercised at BARDA’s sole discretion. We must complete agreed upon milestones and deliverables in each discrete work segment before the next option segment is eligible to be exercised. Under the contract as currently in effect, if each follow-on option segment is exercised by BARDA, we may receive up to $75.8 million in expense reimbursement and $5.3 million in fees.

We are currently completing the base performance segment of the contract under which we may receive up to a total of $31.0 million. The term of the base segment ends on May 31, 2013. BARDA must notify us at least 30 days before the end of the current base performance segment if it intends to exercise the first option segment of the contract. If all option segments are exercised by BARDA, the term of the contract would be extended to February 15, 2016.

Pursuant to the contract, Chimerix and the U.S. government share the rights to any inventions made in the performance of our work under the contract. Specifically, the U.S. government retains a nonexclusive, nontransferable, irrevocable, paid up license to any invention made in the performance of our work under the contract; provided, however, that the U.S. government may, under certain circumstances, including circumstances involving public health and safety, license such inventions to third parties without our consent. There have been no inventions made to date under the BARDA contract.

The contract may be terminated by BARDA ten days after giving us notice of a material default which remains uncured for ten days. In addition, BARDA is also permitted under applicable law to terminate the contract if it is in the U.S. government’s best interest.

We anticipate renegotiating certain aspects of the smallpox animal plan to take into account recent guidance from the FDA for development of CMX001 under the Animal Efficacy Rule. The results of this negotiation are uncertain and we do not anticipate continuing this program without ongoing support from BARDA.

NIAID

In September 2003, we were awarded a $36.3 million grant from the NIAID to support our development of an oral drug for the treatment of smallpox. The work performed under this grant resulted in our selection

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of CMX001 as a lead product candidate for commercial development. The grant, and our activities conducted in connection therewith, were concluded in February 2011.

The U.S. government retained “march-in” and other rights with respect to inventions developed by us under the NIAID contract, and if the U.S. government exercised these rights, we could be obligated, for example, to license intellectual property developed by us on terms unfavorable to us, and there can be no assurance that we would receive compensation from the U.S. government for the exercise of such rights.

Commercialization, Marketing and Sales

Given our stage of development, we have not yet established a commercial organization or distribution capabilities.

Due to the complexity of HSCT and SOT treatment regimens, treating physicians are readily identifiable and are well informed, which may make it easier to identify potential prescribers after a drug is approved. Patients who receive HSCT and SOTs will mostly likely be treated at a small number of major medical centers by specialized teams of physicians. In the United States, there are approximately 200 institutions at which transplants are performed, of which approximately 75% perform HSCTs and 75% perform SOTs. Due to the different requirements and treatment regimens for HSCT and SOT patients, only approximately one-third of these hospitals perform both HSCT and SOTs. Of the approximately 150 hospitals that perform HSCTs, approximately 50 perform both pediatric and adult transplants, approximately 60 perform adult transplants only and approximately 40 perform pediatric HSCTs only.

The management of therapies for transplant patients is largely the responsibility of the transplant physicians and an even smaller subset of specialists in infectious diseases who oversee post-transplant therapies. In many hospitals, the infectious disease physicians are responsible for only HSCT or only SOT patients, and often further sub-specialize to pediatric versus adult transplant patients. Overall, transplant and transplant infectious disease treatment is a small clinical discipline with a clearly identified group of key opinion leaders. While the standard of care for post-transplant therapies varies from institution to institution and from country to country, it is often driven by research activities or publications of these key opinion leaders from academic transplant research centers. Many of these key opinion leaders have participated in our clinical trials and/or have experience using CMX001 through our Compassionate Use Program.

If approved for the prevention of CMV in patients who have received HSCT, we believe that it will be possible for us to commercialize CMX001 for this indication with a relatively small specialty sales force that calls on a limited and focused group of physicians. For the United States and Canada, we foresee the need for a full commercial infrastructure of approximately 50 people. While our commercialization efforts would initially be focused on physicians who are responsible for HSCT patients, this sales and marketing infrastructure would serve as the foundation for an expanded focus on physicians who are responsible for SOT patients, subject to marketing approval in this patient population.

Outside of the United States, subject to obtaining necessary marketing approvals, we likely will seek to commercialize CMX001 through distribution or other collaboration arrangements. If we elect to develop CMX001 for other dsDNA indications, we would plan to do so selectively either on our own or by establishing alliances with one or more pharmaceutical company collaborators, depending on, among other things, the applicable indications, the related development costs and our available resources.

Competition

Our industry is highly competitive and subject to rapid and significant technological change. Our potential competitors include large pharmaceutical and biotechnology companies, specialty pharmaceutical and generic drug companies, academic institutions, government agencies and research institutions. We believe that the key competitive factors that will affect the development and commercial success of CMX001 and the product candidates that we develop are efficacy, safety and tolerability profile, convenience in dosing, product labeling, value, price and the availability of reimbursement from the government and other third-parties. Our commercial opportunity could be reduced or eliminated if our competitors have products which are better in one or more of these categories.

We expect that, if approved, CMX001 would compete with a number of existing products and other product candidates that target serious viral infections. Many of our potential competitors have substantially

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greater financial, technical, commercial and human resources than we do and significantly more experience in the discovery, development and regulatory approvals of product candidates, and the commercialization of those products. Accordingly, our competitors may be more successful than we may be in obtaining FDA approval for product candidates and achieving widespread market acceptance. Our competitors’ products and product candidates may be more effective, or more effectively marketed and sold, than any product candidate we may commercialize, which could render CMX001 or any other product candidate that we develop obsolete or non-competitive before we can recover the expenses of developing and commercializing any such product candidate. We anticipate that we will face intense and increasing competition as new products enter the market, as advanced technologies become available and as generic forms of currently branded products become available. Finally, the development of new treatment methods for the diseases we are targeting could render our product candidates non-competitive or obsolete. Changes in the health care system may limit our ability to price CMX001 or our other products at a level that would allow recovery of our research and development costs and may impede our ability to generate or maintain a profit.

We anticipate that, if approved, CMX001 will compete with other antiviral products, including drugs and vaccines which demonstrate efficacy against viruses that affect our target patient populations. These include both oral and intravenous ganciclovir, a drug that is sold by generic manufacturers; Valcyte® (valganciclovir), a prodrug of ganciclovir that is marketed by Hoffmann-La Roche Inc.; Cytogam®, a pooled CMV hyperimmuneglobulin, marketed by CSL Limited; Vistide® (cidofovir for injection), marketed by Gilead; and Foscavir® (foscarnet sodium for injection), marketed by Clinigen Group plc and generic manufacturers.

We are aware of several product candidates currently in development that may compete against CMX001, including letermovir, an anti-CMV drug being developed pursuant to an exclusive worldwide license agreement between AiCuris and Merck.

We are aware of several therapeutic vaccine candidates that are being studied for the prevention or mitigation of CMV infection in a variety of settings. One such vaccine, TransVax, was licensed to Astellas from Vical and is being developed by Astellas and Vical. Other vaccine products are being developed by GlaxoSmithKline plc (GlaxoSmithKline), Novartis International AG, sanofi-aventis Group (Aventis), and a variety of university and governmental organizations.

Other products used against the same viruses targeted by CMX001 include valacyclovir, an antiviral drug marketed by GlaxoSmithKline and a number of generic manufacturers; leflunomide, a drug approved for rheumatoid arthritis and sold in the United States by Aventis under the brand name Arava®; and quinolone antibiotics, which are manufactured by a variety of branded pharmaceutical companies and generic manufacturers.

Our commercial opportunity could be reduced or eliminated if our competitors develop and commercialize products that are safer, more effective, have fewer or less severe side effects, are more convenient or are less expensive than CMX001 or any other product candidate that we may develop. Our competitors also may obtain FDA or other regulatory approval for their products more rapidly than we may obtain approval for ours. In addition, our ability to compete may be affected because in many cases insurers or other third-party payers seek to encourage the use of generic products.

We believe that CMX001 has potential benefits over these competitive products as described in more detail under “Business — CMX001 Background and Development Strategy.” As a result, we believe that CMX001 should be well placed to capture market share from competing products if we obtain the required regulatory approvals for CMX001. However, even with those benefits, we may not be able to make promotional claims that CMX001 is superior to these competing products, and CMX001 may be unable to compete successfully against these products. See “Risk Factors — Risks Related to Commercialization of Our Product Candidates.”

Intellectual Property

We strive to protect and enhance the proprietary technologies that we believe are important to our business, and seek to obtain and maintain patents intended to cover our products and compositions, their

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methods of use and any other inventions that are important to the development of our business. We are not currently aware of any third-party patents (other than patents we have licensed) encompassing our proprietary compounds CMX001 and CMX157.

Our success will depend significantly on our ability to obtain and maintain patent and other proprietary protection for commercially important technology, inventions and know-how related to our business, defend and enforce our patents, maintain our licenses to use intellectual property owned by third parties, preserve the confidentiality of our trade secrets and operate without infringing the valid and enforceable patents and other proprietary rights of third parties. We also rely on know-how, continuing technological innovation and in-licensing opportunities to develop, strengthen, and maintain our proprietary position in the field of nucleoside phosphonates.

We believe that we have a strong intellectual property position and substantial know-how relating to the development and commercialization of our lipid-antiviral conjugates, including CMX001, CMX157, and derivatives of CMX001 or CMX157, consisting of patents or patent applications that we own or have in-licensed from third parties. We cannot be sure that patents will be granted with respect to any of our pending patent applications or with respect to any patent applications filed by us in the future, nor can we be sure that any of our existing patents or any patents that may be granted to us in the future will be commercially useful in protecting our technology.

Our objective is to continue to expand our intellectual property estate by filing patent applications directed to dosage forms, methods of treatment, and identification of additional nucleoside phosphonate compounds and their derivatives, in order to protect our lipid-antiviral conjugate therapeutics and to maintain our position in the antiviral field. Specifically, we seek patent protection in the United States and in certain other jurisdictions for novel compositions of matter covering CMX001 and CMX157, and chemistries which facilitate the synthesis of nucleoside phosphonate compounds, including CMX001 and CMX157, as well as uses of these compounds in a variety of anti-viral therapies, where available and when appropriate. Our policy is to pursue, maintain, and defend patent rights, whether developed internally or licensed from third parties, and to protect the technology, inventions, and improvements that are commercially important to the development of our business. We are also expanding our intellectual property estate into the area of novel anti-fungal nucleoside phosphonates.

CMX001

The patent portfolio for CMX001 is directed to cover compositions of matter, formulation, manufacturing methods, and methods of use. This patent portfolio includes issued U.S. patents, pending U.S. patent applications, and corresponding foreign national and regional counterpart patents and patent applications. The patents and patent applications relating to CMX001 include patent applications owned by us, as well as patents and patent applications in-licensed (exclusive license) from The Regents of the University of California. The issued composition of matter patents (U.S. Patent Nos. 6,716,825; 7,034,014; 7,094,772; and 7,790,703), if the appropriate maintenance, renewal, annuity, and other government fees are paid, are expected to expire in 2020. The issued methods of use patents (U.S. Patent Nos. 6,716,825; 7,452,898; and 7,790,703), if the appropriate maintenance, renewal, annuity, and other government fees are paid, are expected to expire in 2020. Based on our current development plan, we believe that an additional term of up to five years for one of the CMX001 U.S. patents may result from the patent term extension provision of the Hatch-Waxman Amendments of 1984 (the Hatch-Waxman Act). We expect that the patent applications in this portfolio, if issued, and if appropriate maintenance, renewal, annuity, and other governmental fees are paid, would expire between 2020 and 2031, excluding any additional term from patent term adjustment or patent term extension. Assuming one of the U.S. composition of matter or method of use patents covering CMX001 were awarded the maximum patent term extension, the term of that patent could extend to December 2025. The patent term calculation method and the provisions under the Hatch-Waxman Act are described under “— Patent Term” below.

The term of issued CMX001 composition of matter patents in other jurisdictions (Australia, Canada, Europe, Hong Kong, India, Japan, Mexico, Russia, and South Africa) and methods of use patents and patent applications (if applicable) relating to CMX001 (in Australia, Canada, China, Europe, Hong Kong, India, Japan, Mexico, Russia, and South Africa), if the appropriate maintenance, renewal, annuity, and other

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government fees are paid, are expected to expire between 2020 and 2031. These patents and patent applications (if applicable), depending on the national laws, may benefit from extension of patent term in individual countries. In the European Union member countries, for example, a supplementary protection certificate (SPC), if obtained, provides a maximum five years of market exclusivity. The duration of the SPC can be extended to five and a half years when the SPC relates to a human medicinal product for which data from clinical trials conducted in accordance with an agreed Pediatric Investigation Plan (PIP) have been submitted. Likewise, in Japan, the term of a patent may be extended by a maximum of five years in certain circumstances.

CMX157

The patent portfolio for CMX157 is directed to cover compositions of matter, formulation, and methods of use. This patent portfolio includes issued U.S. patents, pending U.S. patent applications, and corresponding foreign national and regional counterpart patents and patent applications. The patents and patent applications relating to CMX157 include patent applications owned by us, as well as patents and patent applications in-licensed (exclusive license) from The Regents of the University of California. The issued composition of matter patents (U.S. Patent Nos. 6,716,825; 7,034,014; 7,094,772; 7,790,703; and 7,687,480), if the appropriate maintenance, renewal, annuity, and other government fees are paid, are expected to expire in 2020. The issued methods of use patents (U.S. Patent Nos. 6,716,825; 7,790,703; and 7,687,480), if the appropriate maintenance, renewal, annuity, and other government fees are paid, are expected to expire in 2020. We believe that an additional term of up to five years for one of the CMX157 U.S. patents may result from the patent term extension provision of the Hatch-Waxman Act. We expect that the patent applications in this portfolio, if issued, and if appropriate maintenance, renewal, annuity, and other governmental fees are paid, would expire between 2020 and 2031, excluding any additional term from patent term adjustment or patent term extension. The patent term calculation method and the provisions under the Hatch-Waxman Act are described in the “Patent Term” section below.

The term of issued CMX157 composition of matter patents in other jurisdictions (Australia, Canada, Europe, Hong Kong, India, Japan, Mexico, Russia, and South Africa) and methods of use patents and patent applications (if applicable) relating to CMX157 (in Australia, Canada, China, Europe, Hong Kong, India, Japan, Mexico, Russia, and South Africa), if the appropriate maintenance, renewal, annuity, and other government fees are paid, are expected to expire between 2020 and 2031. Like the patents relating to CMX001, the patents and patent applications (if applicable), covering CMX157, depending on the national laws, may also benefit from extension of patent term in individual countries.

Other Product Candidates

In addition to CMX001 and CMX157, we have a chemical library of more than 10,000 heterocyclic compounds purchased from the University of Michigan which includes approximately 3,500 nucleoside analog candidates for lipid conjugation. We also license certain intellectual property rights relating to these compounds from the University of Michigan, in exchange for which we agree, among other things, to use commercially reasonable efforts to develop and commercialize products utilizing the licensed intellectual property, and to pay certain royalties and other fees to the University of Michigan. Focused screening of the library has identified viable hits against multiple pathogens including compounds with activity against influenza, clinically important fungi and compounds with activity against both CMV and BKV. Lead selection is in progress for the antifungal and dual active CMV/BKV programs. We believe additional nucleoside phosphonate antiviral compounds, unrelated to CMX001 and CMX157, are protected under U.S. Patents 7,994,143 and 7,749,983, which are expected to expire between 2027 and 2028, if the appropriate maintenance, renewal, annuity, and other government fees are paid.

Patent Term

The term of individual patents and patent applications listed in previous sections will depend upon the legal term of the patents in the countries in which they are obtained. In most countries, the patent term is 20 years from the date of filing of the patent application (or parent application, if applicable). For example, if an international (PCT) application is filed, any patent issuing from the PCT application in a specific country expires 20 years from the filing date of the PCT application. In the United States, however, if a patent was in

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force on June 8, 1995, or issued on an application that was filed before June 8, 1995, that patent will have a term that is the greater of twenty years from the filing date or seventeen years from the date of issue.

Under the Hatch-Waxman Act, the term of a patent that covers an FDA-approved drug may also be eligible for patent term extension (PTE). PTE permits patent term restoration of a U.S. patent as compensation for the patent term lost during the FDA regulatory review process. The Hatch-Waxman Act permits a patent term extension of up to five years beyond the expiration of the patent. The length of the patent term extension is related to the length of time the drug is under regulatory review. A patent term extension cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval and only one patent applicable to an approved drug may be extended. Similar provisions may be available in Europe and certain other foreign jurisdictions to extend the term of a patent that covers an approved drug. When possible, depending upon the length of clinical trials and other factors involved in the filing of a new drug application (NDA) we expect to apply for patent term extensions for patents covering nucleoside phosphonates and their derivatives, and their use in treating various diseases. As a specific example, if we are awarded the maximum length of PTE, our U.S. granted composition of matter patents relating to CMX001 would have an expected expiration date of December 20, 2025. However, depending on any changes in our clinical path, the PTE may not be granted, or may be less than the maximum.

For additional information on patent term extension and the BPCA, see “Business — Government Regulation and Product Approval.”

Proprietary Rights and Processes

We may rely, in some circumstances, on proprietary technology and processes (including trade secrets) to protect our technology. However, these can be difficult to protect. We seek to protect our proprietary technology and processes, in part, by entering into confidentiality agreements with our employees, consultants, scientific advisors, contractors, and collaborators. We also seek to preserve the integrity and confidentiality of our proprietary technology and processes by maintaining physical security of our premises and physical and electronic security of our information technology systems. While we have confidence in these individuals, organizations and systems, agreements or security measures may be breached, and we may not have adequate remedies for any breach. In addition, our proprietary technology and processes may otherwise become known or be independently discovered by competitors. To the extent that our employees, consultants, scientific advisors, contractors, or collaborators use intellectual property owned by others in their work for us, disputes may arise as to the rights in related or resulting know-how and inventions. For this and more comprehensive risks related to our proprietary technology and processes, please see the section on “Risk Factors — Risks Related to Our Intellectual Property.”

Technology Licenses

The Regents of the University of California

In May 2002, we entered into a license agreement with The Regents of the University of California (UC) under which we obtained an exclusive, worldwide license to UC’s patent rights in certain inventions (the UC Patent Rights) related to lipid-conjugated antiviral compounds and their use, including certain patents relating to CMX001 and CMX157. The agreement was amended in September 2002 in order to expand the scope of the license and again in December 2010 in order to modify certain financial terms. The agreement was amended a third time in September 2011 to add additional patents related to certain metabolically stable lipid-conjugate compounds. A fourth amendment was executed in July 2012 to alter the rights and obligations of the parties in light of our current business plans.

Under the license agreement, we are permitted to research, develop, manufacture and commercialize products utilizing the UC Patent Rights for all human and veterinary uses, and to sublicense such rights. UC retained the right, on behalf of itself and other non-profit institutions, to use the UC Patent Rights for educational and research purposes and to publish information about the UC Patent Rights.

In consideration for the rights granted to us under the license agreement, we have issued UC an aggregate of 64,788 shares of our common stock. As additional consideration, we are required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are

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covered by the UC Patent Rights, plus certain annual fees to maintain such patents until we commercialize a product utilizing UC Patent Rights. In connection with the development and commercialization of CMX001 and CMX157, we could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement. In addition, upon commercialization of any product utilizing the UC Patent Rights (which would include the commercialization of CMX001 or CMX157), we will be required to pay low single digit royalties on net sales of such product.

In the event we sublicense a UC Patent Right (including UC Patent Rights relating to CMX001 or CMX157), we are obligated to pay to UC a fee, which amount will vary depending upon the size of any upfront payment we receive and the clinical development stage of the compound being sublicensed, but which could be up to approximately 50% of the sublicense fee in certain circumstances. In addition, we will also be required to pay to UC a low single digit sublicense royalty on net sales of products that use the sublicensed UC Patent Rights, but in no event will we be required to pay more than 50% of the royalties we receive in connection with the relevant sublicense. Any such royalty payment will be reduced by other payments we are required to make to third parties until a minimum royalty has been reached. As of December 31, 2012, we had paid an aggregate of approximately $1.2 million to UC pursuant to the license agreement.

The license agreement requires that we diligently develop, manufacture and commercialize compounds that are covered by the UC Patent Rights, and we have agreed to meet certain development and commercialization milestones. UC may, at its option, either terminate the license agreement or change the license granted from an exclusive license to a non-exclusive license if we fail to meet such development and commercialization milestones. We are currently in compliance with these milestone requirements. Specifically, Section 3.3(a)(5) of the license agreement contains a due diligence requirement stating that we must commence a Phase III clinical trial for the first Licensed Product within 9 years of the Effective Date (as those terms are defined within the license agreement). On January 31, 2011 we received a letter from UC stating that we had satisfied the requirements of Section 3.3(a)(5), thereby waiving compliance with further due diligence obligations under Section 3.3(a)(5).

We may terminate the license agreement upon 90 days’ notice to UC. UC may terminate the license agreement in the event of our nonperformance or breach of the license agreement which remains uncured after 60 days of receiving written notice of such nonperformance or breach. Absent early termination, the license agreement will automatically terminate upon the later of the expiration date of the longest-lived patent right included in the UC Patent Rights, which is currently expected to be in October 2028, or the 21^st anniversary of the effective date of the agreement, which would be May 2023.

Other

We also license intellectual property from certain other parties that we believe to be necessary or useful for the conduct of our business, including from the University of Michigan, and may enter into additional license agreements in the future.

Manufacturing

We do not own or operate and we do not expect to own or operate, facilities for product manufacturing, storage and distribution, or testing. In the past, we have relied on third-party manufacturers for supply of our lead product candidate, CMX001, as well as our other product candidates. We expect that in the future we will rely on such manufacturers for supply of drug substance and product that will be used in clinical trials of CMX001. When produced on a commercial scale, we expect that cost-of-goods-sold relating to CMX001 will generally be in-line with that of other small-molecule pharmaceutical compounds.

The manufacturing process for CMX001 is relatively straight-forward and generally in-line with other small molecule pharmaceutical compounds in terms of cost and complexity. The process is robust and reproducible, does not require dedicated reactors or specialized equipment, uses common synthetic chemistry and readily available materials, including off-the-shelf and made-to-order starting materials, and is readily transferable.

Our current drug substance supply chain for CMX001 involves various contractors that supply the raw materials for the drug substance process and a contract manufacturer for the drug substance. We have validated the drug substance production process for CMX001 at a scale of 100 kilograms, which is an amount

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that far exceeds our anticipated commercial requirements. We are currently transferring the drug substance manufacturing process to our selected contractor that will produce the commercial supply of drug substance. Changes in our requirements may require revalidation of the manufacturing process at a different scale and potentially at a different contractor depending on the necessary scale, infrastructure and technical capabilities. To ensure continuity in our supply chain, we plan to establish supply arrangements with alternative suppliers for certain portions of our supply chain, as appropriate.

Our drug products (tablets and suspension) are also manufactured under contract. We have validated manufacturing of CMX001 tablets at a 165 kg commercial scale. In addition, stability data are available to support sufficient commercial shelf life. We have also developed a suspension formulation for CMX001 and have manufactured that formulation at pilot scale. We are currently evaluating manufacturers to optimize tablet and suspension formulation production to meet forecasted commercial demand.

Manufacturing is subject to extensive regulations that impose various procedural and documentation requirements, which govern record keeping, manufacturing processes and controls, personnel, quality control and quality assurance, among others. Our systems and contractors are required to be in compliance with these regulations, and this is assessed regularly through monitoring of performance and a formal audit program. We have personnel with extensive technical, manufacturing, analytical and quality experience and strong project management discipline to oversee contract manufacturing and testing activities, and to compile manufacturing and quality information for our regulatory submissions.

Pursuant to our license agreement with Merck, the manufacture of CMX157 is under the control and direction of Merck.

Government Regulation and Product Approval

Government authorities in the United States at the federal, state and local level, and in other countries extensively regulate, among other things, the research, development, testing, manufacture, quality control, approval, labeling, packaging, storage, record-keeping, promotion, advertising, distribution, post-approval monitoring and reporting, marketing and export and import of products such as those we are developing. CMX001 and any other drug candidate that we develop must be approved by the FDA before they may be legally marketed in the United States and by the corresponding foreign regulatory agencies before they may be legally marketed in foreign countries.

United States Drug Development Process

In the United States, the FDA regulates drugs under the Federal Food, Drug and Cosmetic Act (FDCA) and implementing regulations. Drugs are also subject to other federal, state and local statutes and regulations. The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local and foreign statutes and regulations requires the expenditure of substantial time and financial resources. Failure to comply with the applicable requirements at any time during the product development process, approval process or after approval, may subject an applicant to a variety of administrative or judicial sanctions, such as the FDA’s refusal to approve pending applications, withdrawal of an approval, imposition of a clinical hold, issuance of warning letters, product recalls, product seizures, total or partial suspension of production or distribution injunctions, fines, refusals of government contracts, restitution, disgorgement of profits or civil or criminal penalties. Any agency or judicial enforcement action could have a material adverse effect on us. The process required by the FDA before a drug may be marketed in the United States generally involves the following:

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The lengthy process of seeking required approvals and the continuing need for compliance with applicable statutes and regulations require the expenditure of substantial resources and approvals are inherently uncertain.

Before testing any compounds with potential therapeutic value in humans, the drug candidate enters the preclinical testing stage. Preclinical tests include laboratory evaluations of product chemistry, toxicity and formulation, as well as animal studies to assess the potential safety and activity of the drug candidate. The conduct of the preclinical tests must comply with federal regulations and requirements including good laboratory practices. The IND sponsor must submit the results of the preclinical tests, together with manufacturing information, analytical data, any available clinical data or literature and a proposed clinical protocol, among other things, to the FDA as part of the IND. The IND automatically becomes effective 30 days after receipt by the FDA, unless before that time the FDA raises concerns or questions related to one or more proposed clinical trials and places the trial on a clinical hold within that 30-day time period. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical trial can begin. The FDA may also impose clinical holds on a drug candidate at any time before or during clinical trials due to safety concerns or non-compliance. Accordingly, we cannot be sure that submission of an IND will result in the FDA allowing clinical trials to begin, or that, once begun, issues will not arise that suspend or terminate such trial. We have provided CMX001 to individual patients under expanded access and comparable compassionate use programs outside the United States.

Clinical trials involve the administration of the drug candidate to healthy subjects or patients with the target disease under the supervision of qualified investigators, generally physicians not employed by or under the trial sponsor’s control. Clinical trials are conducted under written study protocols detailing, among other things, the objectives of the clinical trial, dosing procedures, subject selection and exclusion criteria, and the parameters to be used to monitor subject safety. Each protocol must be submitted to the FDA as part of the IND. Clinical trials must be conducted in accordance with the FDA’s regulations which embody the ICH GCP requirements. Further, each clinical trial must be reviewed and approved by an IRB at or servicing each institution at which the clinical trial will be conducted. An IRB is charged with protecting the welfare and rights of trial participants and considers such items as whether the risks to individuals participating in the clinical trials are minimized and are reasonable in relation to anticipated benefits. The IRB also approves the informed consent form that must be provided to each clinical trial subject or his or her legal representative and must monitor the clinical trial until it is completed.

Human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

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Post-approval studies, or Phase 4 clinical trials, may be conducted after initial marketing approval. These studies are used to gain additional experience from the treatment of patients in the intended therapeutic indication and may be required by the FDA as part of the approval process.

Progress reports detailing the status of drug development and results of the clinical trials must be submitted at least annually to the FDA and written IND safety reports must be submitted to the FDA and the investigators for serious and unexpected adverse events or any finding from tests in laboratory animals that suggests a significant risk for human subjects or patients. Phase 1, Phase 2 and Phase 3 clinical trials may not be completed successfully within any specified period, if at all. The FDA or the sponsor or its data safety monitoring board may suspend a clinical trial at any time on various grounds, including a finding that the research subjects are being exposed to an unacceptable health risk. Similarly, an IRB can suspend or terminate approval of a clinical trial at its institution if the clinical trial is not being conducted in accordance with the IRB’s requirements or if the drug has been associated with unexpected serious harm to study subjects.

Concurrent with clinical trials, companies usually complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the drug as well as finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the drug candidate and, among other things, the manufacturer must develop methods for testing the identity, strength, quality and purity of the final drug product. Additionally, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the drug candidate does not undergo unacceptable deterioration over its shelf life.

The Animal Efficacy Rule

The FDA amended its regulations, effective June 30, 2002, to include what is frequently referred to as the “Animal Efficacy Rule” whereby the FDA may approve for marketing certain new drug and biological products used to reduce or prevent the toxicity of chemical, biological, radiological, or nuclear agents not otherwise naturally present in circumstances that would permit the typical clinical testing regime, based on evidence of safety in healthy subjects and evidence of effectiveness derived only from appropriate animal studies and any additional supporting data. In addition to seeking approval for the prevention of CMV infection after the conduct of clinical studies, we anticipate that we will seek approval for therapeutic use of CMX001 in the treatment of smallpox using the animal efficacy rule.

U.S. FDA Review and Approval Processes

The results of product development, preclinical studies and clinical trials, along with descriptions of the manufacturing process, analytical tests conducted on the chemistry of the drug, proposed labeling and other relevant information are submitted to the FDA as part of an NDA requesting approval to market the product. The submission of an NDA is subject to the payment of substantial user fees; a waiver of such fees may be obtained under certain limited circumstances.

In addition, under the Pediatric Research Equity Act (PREA) an NDA or supplement to an NDA must contain data to assess the safety and effectiveness of the drug for the claimed indications in all relevant

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pediatric subpopulations and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The FDA may grant deferrals for submission of pediatric data or full or partial waivers. Unless otherwise required by regulation, PREA does not apply to any drug for an indication for which orphan designation has been granted.

The FDA reviews all NDAs submitted before it accepts them for filing and may request additional information rather than accepting an NDA for filing. Once the submission is accepted for filing, the FDA begins an in-depth review of the NDA. Under the goals and policies agreed to by the FDA under the Prescription Drug User Fee Act (PDUFA) the FDA has 12 months after submission of an NDA in which to complete its initial review of a standard NDA and respond to the applicant, and eight months for a priority review NDA. The FDA does not always meet its PDUFA goal dates for review of standard and priority review NDAs. The review process and the PDUFA goal date may be extended by three months if the FDA requests or the NDA sponsor otherwise provides additional information or clarification regarding information already provided in the submission at any time during the review cycle.

The FDA reviews the NDA to determine, among other things, whether the proposed product is safe and effective for its intended use, and whether the product is being manufactured in accordance with cGMP to assure and preserve the product’s identity, strength, quality and purity. The FDA may refer applications for novel drug or biological products or drug or biological products which present difficult questions of safety or efficacy to an advisory committee, typically a panel that includes clinicians and other experts, for review, evaluation and a recommendation as to whether the application should be approved and under what conditions. The FDA is not bound by the recommendations of an advisory committee, but it considers such recommendations carefully when making decisions. During the drug approval process, the FDA also will determine whether a risk evaluation and mitigation strategy (REMS) is necessary to assure the safe use of the drug. If the FDA concludes a REMS is needed, the sponsor of the NDA must submit a proposed REMS; the FDA will not approve the NDA without a REMS, if required.

Before approving an NDA, the FDA will inspect the facilities at which the product is to be manufactured. The FDA will not approve the product unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product within required specifications. Additionally, before approving an NDA, the FDA will typically inspect one or more clinical sites to assure compliance with FDA regulations regarding conduct of clinical trials for the product’s trials. If the FDA determines that the application, manufacturing process or manufacturing facilities are not acceptable, it will outline the deficiencies in the submission and often will request additional testing or information.

The NDA review and approval process is lengthy and difficult and the FDA may refuse to approve an NDA if the applicable regulatory criteria are not satisfied or may require additional clinical data or other data and information. Even if such data and information is submitted, the FDA may ultimately decide that the NDA does not satisfy the criteria for approval. Data obtained from clinical trials are not always conclusive and the FDA may interpret data differently than we interpret the same data, which could delay, limit or prevent regulatory approval. The FDA will issue a “complete response” letter if the agency decides not to approve the NDA. The complete response letter usually describes all of the specific deficiencies in the NDA identified by the FDA. The deficiencies identified may be minor, for example, requiring labeling changes, or major, for example, requiring additional clinical trials. Additionally, the complete response letter may include recommended actions that the applicant might take to place the application in a condition for approval. If a complete response letter is issued, the applicant may either resubmit the NDA, addressing all of the deficiencies identified in the letter, or withdraw the application.

If a product receives regulatory approval, the approval may be significantly limited to specific diseases and dosages or the indications for use may otherwise be limited, which could restrict the commercial value of the product. Further, the FDA may require that certain contraindications, warnings or precautions be included in the product labeling. In addition, the FDA may require Phase 4 testing, which involves clinical trials designed to further assess a product’s safety and effectiveness and may require testing and surveillance programs to monitor the safety of approved products that have been commercialized.

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Expedited Development and Review Programs

The FDA has a “Fast Track” program that is intended to expedite or facilitate the process for reviewing new drug products that meet certain criteria. Specifically, new drug products are eligible for Fast Track designation if they are intended to treat a serious or life-threatening condition and demonstrate the potential to address unmet medical needs for the condition. Fast Track designation applies to the combination of the product and the specific indication for which it is being studied. Unique to a Fast Track product, the FDA may consider for review sections of the NDA on a rolling basis before the complete application is submitted, if the sponsor provides a schedule for the submission of the sections of the NDA, the FDA agrees to accept those sections and determines that the schedule is acceptable, and the sponsor pays any required user fees upon submission of the first section of the NDA.

Any product submitted to the FDA for marketing approval, including those submitted to a Fast Track program, may also be eligible for other types of FDA programs intended to expedite development and review, such as priority review and accelerated approval. Any product is eligible for priority review if it has the potential to provide safe and effective therapy where no satisfactory alternative therapy exists or there is a significant improvement in the treatment, diagnosis or prevention of a disease compared with marketed products. The FDA will attempt to direct additional resources to the evaluation of an application for a new drug product designated for priority review in an effort to facilitate the review. Additionally, a product may be eligible for accelerated approval. Drug products studied for their safety and effectiveness in treating serious or life-threatening illnesses and that provide meaningful therapeutic benefit over existing treatments may receive accelerated approval, which means that they may be approved on the basis of adequate and well-controlled clinical studies establishing that the product has an effect on a surrogate endpoint that is reasonably likely to predict a clinical benefit, or on the basis of an effect on a clinical endpoint other than survival or irreversible morbidity. As a condition of approval, the FDA generally requires that a sponsor of a drug product receiving accelerated approval perform adequate and well-controlled post-marketing clinical studies to establish safety and efficacy for the approved indication. Failure to conduct such studies, or conducting such studies that do not establish the required safety and efficacy, may result in revocation of the original approval. In addition, the FDA currently requires as a condition for accelerated approval pre-approval of promotional materials, which could adversely impact the timing of the commercial launch or subsequent marketing of the product. Fast Track designation, priority review and accelerated approval do not change the standards for approval but may expedite the development or approval process.

Post-Approval Requirements

Any drug products for which we receive FDA approvals are subject to continuing regulation by the FDA, including, among other things, record-keeping requirements, reporting of adverse experiences with the product, providing the FDA with updated safety and efficacy information, product sampling and distribution requirements, complying with certain electronic records and signature requirements and complying with FDA promotion and advertising requirements. These promotion and advertising requirements include, among other things, standards for direct-to-consumer advertising, prohibitions against promoting drugs for uses or in patient populations that are not described in the drug’s approved labeling (known as “off-label use”), rules for conducting industry-sponsored scientific and educational activities, and promotional activities involving the internet. Failure to comply with FDA requirements can have negative consequences, including adverse publicity, enforcement letters from the FDA, mandated corrective advertising or communications with doctors, and civil or criminal penalties. Although physicians may prescribe legally available drugs for off-label uses, manufacturers may not market or promote such off-label uses.

We rely, and expect to continue to rely, on third parties for the production of clinical and commercial quantities of our products as discussed under “— Manufacturing” above. Manufacturers of our products are required to comply with applicable FDA manufacturing requirements contained in the FDA’s cGMP regulations. cGMP regulations require among other things, quality control and quality assurance as well as the corresponding maintenance of records and documentation. Drug manufacturers and other entities involved in the manufacture and distribution of approved drugs are also required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMP and other laws. Accordingly, manufacturers must continue to expend time, money, and effort in the area of production and quality control to maintain cGMP compliance. Discovery

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of problems with a product after approval may result in restrictions on a product, manufacturer, or holder of an approved NDA. These restrictions may include suspension of a product until the FDA is assured that quality standards can be met, continuing oversight of manufacturing by the FDA under a “consent decree,” which frequently includes the imposition of costs and continuing inspections over a period of many years, as well as possible withdrawal of the product from the market. In addition, changes to the manufacturing process generally require prior FDA approval before being implemented. Other types of changes to the approved product, such as adding new indications and additional labeling claims, are also subject to further FDA review and approval.

The FDA also may require post-marketing testing, known as Phase 4 testing, as well as risk minimization action plans and surveillance to monitor the effects of an approved product or place conditions on an approval that could otherwise restrict the distribution or use of the product.

Europe/Rest of World Government Regulation

In addition to regulations in the United States, we will be subject to a variety of regulations in other jurisdictions governing, among other things, clinical trials and any commercial sales and distribution of our products.

Whether or not we obtain FDA approval for a product, we must obtain the requisite approvals from regulatory authorities in foreign countries prior to the commencement of clinical trials or marketing of the product in those countries. Certain countries outside of the United States have a similar process that requires the submission of a clinical trial application much like the IND prior to the commencement of human clinical trials. In the European Union, for example, a clinical trial application (CTA) must be submitted to each country’s national health authority and an independent ethics committee, much like the FDA and IRB, respectively. Once the CTA is approved in accordance with a country’s requirements, clinical trial development may proceed.

The requirements and process governing the conduct of clinical trials, product licensing, pricing and reimbursement vary from country to country. In all cases, the clinical trials are conducted in accordance with the ICH GCP and the applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki.

To obtain regulatory approval of an investigational drug or biological product under European Union regulatory systems, we must submit a marketing authorization application to the European Medicines Agency. The application used to submit the NDA in the United States is similar to that required in the European Union, with the exception of, among other things, country-specific document requirements. For other countries outside of the European Union, such as countries in Eastern Europe, Latin America or Asia, the requirements governing the conduct of clinical trials, product licensing, pricing and reimbursement vary from country to country. In all cases, again, the clinical trials are conducted in accordance with applicable regulatory requirements, ICH GCP and the ethical principles that have their origin in the Declaration of Helsinki.