The trial also included additional secondary endpoints to evaluate CFTR protein function, including CFTR protein trafficking, and lung function. Additional sub-analyses are ongoing to determine any potential trends in other measures of CFTR-dependent chloride ion transport, such as nasal potential difference; or CFTR maturation, as measured by an exploratory Western blot assay, however no statistically significant changes in these measures were observed in the preliminary analysis of data from this trial. The results from this Phase 2a clinical trial did not show any change in lung function, as measured by FEV₁. Based on the results of this clinical trial, we expect to initiate a combination trial of VX-770 and VX-809 in the second half of 2010 in patients with the F508del mutation on both alleles.

        Prior to the above mentioned Phase 2a clinical trial, we completed two Phase 1 clinical trials of VX-809 in healthy volunteers and a Phase 1 clinical trial of VX-809 in CF patients who carry the F508del mutation on at least one of the two alleles. The first clinical trial in healthy volunteers was a single and multiple-dose trial. The second was a single-dose clinical trial examining the pharmacokinetics and safety of a solid dosage form of VX-809. The Phase 1 clinical trial in patients with CF was an escalating dose pharmacokinetics and safety clinical trial.

Immune-mediated Inflammatory Diseases

VX-509 (investigational oral JAK3 inhibitor for the treatment of immune-mediated inflammatory diseases)

        VX-509 is designed to inhibit Janus kinase 3, or JAK3, which is involved in signaling pathways that control the survival and proliferation of a type of white blood cells referred to as lymphocytes. Because of JAK3's role in lymphocyte biology, we believe it is a promising target for the design of immunosuppressant drugs for treatment of a variety of immune-based diseases. Based on in vitro data, VX-509 appears to be a potent and selective inhibitor of JAK3. We have completed Phase 1 clinical trials of VX-509, including a Phase 1 single dose and a multiple dose-ranging 14-day clinical trial of VX-509 in healthy volunteers.

        In January 2010, we initiated a Phase 2a clinical trial of VX-509 in patients with moderate-to-severe rheumatoid arthritis, or RA, expected to enroll approximately 200 patients. This double-blind, randomized, placebo-controlled trial will evaluate the safety, tolerability and clinical activity of four doses of VX-509. Patients will receive 12 weeks of treatment with VX-509 dosed twice daily compared to placebo. The primary endpoints of the clinical trial are to evaluate safety and to measure clinical signs and symptoms of RA in patients after 12 weeks of treatment. Efficacy assessments will include the American College of Rheumatology criteria—ACR20, ACR50 and ACR70—for defining clinical improvement in patients with RA. ACR20, ACR50 and ACR70 are standardized measures of the number of patients who achieve at least a 20, 50 or 70 percent improvement, respectively, in ACR-specified measures of RA activity. The trial will also utilize disease activity score, or DAS, and European League Against Rheumatism, or EULAR, response criteria as additional efficacy assessments. We expect to obtain interim clinical data from this clinical trial, including measurements of safety, tolerability and clinical activity, as early as the second half of 2010.

        We plan to pursue collaborative opportunities for VX-509 with major pharmaceutical companies, but expect that we would not enter into a collaboration until after the receipt of clinical data from the Phase 2a trial.

Epilepsy

VX-765 (investigational oral Caspase-1 inhibition for the treatment of epilepsy)

        VX-765 is designed to inhibit the interleukin-1 converting enzyme, which is an enzyme that controls the generation of cytokines, IL-1b and IL-18, that are believed to mediate a wide range of immune and inflammatory responses in many cell types. Epilepsy is a chronic neurological disorder that

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is defined by recurrent seizures that are the result of overactive neurons in the brain. Recent studies suggest that inflammation and overproduction of IL-1b may be associated with the initiation and maintenance of epileptic seizures. While there are a number of currently approved anticonvulsant medications used to treat patients with epilepsy, a substantial portion of patients are considered to be treatment-resistant because they continue to have seizures while taking approved anti-epileptic drugs.

        VX-765 has been shown to inhibit acute seizures in preclinical models. In addition, VX-765 has shown activity in preclinical models of chronic epilepsy that do not respond to approved anti-epileptic drugs. VX-765 previously has been dosed in over 100 patients in Phase 1 and Phase 2a clinical trials relating to other indications, including a 28-day Phase 2a clinical trial in patients with psoriasis. We terminated development for psoriasis in 2006 because patients did not show an adequate response to therapy with VX-765. We believe that the data we have from the nonclinical studies together with safety information from previous clinical trials in humans for VX-765 provide a rationale to explore the clinical potential of this drug candidate as a treatment for epilepsy. We expect that VX-765 will be the first clinical drug candidate to target epilepsy through the inflammation pathway.

        The Phase 2a trial for VX-765 we initiated in the first quarter of 2010 is expected to enroll approximately 75 patients with treatment-resistant epilepsy. The double-blind, randomized, placebo-controlled clinical trial is expected to evaluate the safety, tolerability and clinical activity of VX-765. Patients will be monitored for seizure frequency during an initial six week baseline period and then for six weeks while they are receiving treatment with VX-765. The primary endpoints of the trial are safety and tolerability. The secondary endpoints will evaluate clinical efficacy relative to baseline measured by reduction in seizure frequency and number of patients with a 50 percent or greater reduction in seizure frequency versus baseline.

COMMERCIAL ORGANIZATION

        We plan to market telaprevir in North America, and we hold worldwide commercial rights to the other drug candidates in our pipeline. Over the past several years, we have expanded our commercial organization with a focus on building our understanding of the HCV market, developing our commercial strategy for the potential launch of telaprevir, and planning the infrastructure necessary to support future commercial activities. In addition, our commercial organization has continued to provide market insight to our research and development organization regarding VX-770 and our earlier-stage drug candidates.

        We believe that we have developed a deep understanding of the HCV market in the United States. Our understanding incorporates information regarding the current standard of care as well as both patient and health care providers' attitudes toward current and potential, future therapies. Based on this information and the data obtained from our Phase 2 clinical trials of telaprevir, we have begun developing our marketing strategy for telaprevir, which we intend to update and refine as we obtain additional information regarding the potential commercial profile for telaprevir. In particular, we plan to incorporate the information we obtain regarding the efficacy and safety of telaprevir from our registration program into our marketing strategy.

        In the period prior to the anticipated launch of telaprevir, we will expand our commercial organization to an even more significant extent. This expansion will include implementation of internal systems and infrastructure in order to support commercial sales, incorporation of appropriate compliance policies and procedures, establishment of patient-focused programs and hiring a sales force to promote telaprevir, if approved, to health care providers. We are assembling a group of executives with broad experience in marketing, sales, distribution, and reimbursement of drugs. We will continue to expand our commercial infrastructure by hiring a sales management team followed by a commercial sales force in the United States.

        In addition, our government affairs and public policy group has begun the process of advocating with state and federal legislatures, government agencies, public health officials and other policy-makers.

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We are advocating policies that promote life sciences innovation and greater awareness regarding HCV infection.

        Under our collaboration agreement with Janssen we will be reliant on Janssen to effectively market telaprevir in the European Union and the rest of its territory. Mitsubishi Tanabe will market telaprevir in Japan and specified other countries in the Far East. If we obtain approval, we may further develop our own capabilities to market and sell one or more of our other drug candidates in markets outside North America. We are assessing various scenarios to support VX-770, both within and beyond the United States. CF markets tend to be highly concentrated and are therefore accessible through a variety of promotional approaches.

RESEARCH PROGRAMS

        We believe that our integrated drug design approach has significantly enhanced our ability to discover and develop small molecule drug candidates directed at biologically complex targets associated with serious diseases. Our drug design platform integrates biology, pharmacology, drug metabolism and pharmacokinetics, toxicology, material sciences, biophysics, medicinal chemistry and process chemistry, automation and information technologies in a coordinated and simultaneous fashion throughout the discovery process. We believe that our approach has been validated through our success in moving drug candidates into clinical trials. We have decided to focus on several core therapeutic areas, in order to expand and develop our expertise in specific therapeutic areas and to permit a framework for portfolio planning and execution. Currently, the four therapeutic areas of highest priority to us are: infectious diseases, including viral and bacterial infections; IMIDs; cancer; and neurological diseases and disorders, including pain. Driven by the complexity of the therapeutic areas selected, we are attempting to identify multiple targets within each indication that, either as a stand-alone therapy or combination therapy, could provide treatment options that are transformational in nature. The objective of this approach is to enable us to eventually provide multiple drugs in each of these therapeutic areas. We selected these therapeutic areas by mapping our research strengths, including expertise in kinases, proteases and membrane proteins, onto therapeutic areas with high unmet need, with an emphasis on indications where we believe we, independently or in collaboration with other pharmaceutical companies, will be able to discover, develop, and commercialize important medicines for serious diseases. Within each therapeutic area, we intend to focus initially on specific indications.

        Our past drug discovery efforts have produced a variety of drug candidates that have been commercialized or are currently in preclinical or clinical development. We believe our ongoing research programs continue to create value for us by generating new drug candidates in areas of significant unmet medical need. We have commenced preclinical activities for a number of additional investigational compounds, one or more of which may enter clinical development in 2010.

        To augment our internal research programs, we seek to collaborate with leading academic research institutions, government laboratories, foundations and other organizations in order to advance research in our areas of therapeutic interest as well as in areas of basic technological enablement. We have established relationships with organizations and organized consortia of organizations from around the world with expertise in areas of interest to us, and intend to leverage that experience to further our research efforts. For example, we have entered into a collaboration with CHDI Foundation, Inc., a non-profit foundation committed to accelerating the discovery and development of new drugs that delay the onset or slow the progression of Huntington's disease. This collaboration is aimed at developing assays for use in discovering novel compounds for the treatment of Huntington's disease.

CORPORATE COLLABORATIONS

        We have entered into corporate collaborations with pharmaceutical and other companies and organizations that provide financial and other resources, including capabilities in research, development, manufacturing, and sales and marketing, to support our research and development programs.

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Janssen Pharmaceutica, N.V.

        In June 2006, we entered into a license, development, manufacturing and commercialization agreement with Janssen. Under the collaboration agreement, we collaborate with Janssen to develop and commercialize telaprevir. Under the terms of the collaboration agreement, we retain exclusive commercial rights to telaprevir in North America and lead the development plan for telaprevir in North America and the Janssen territories. Janssen has exclusive rights to commercialize telaprevir outside of North America and the Far East. In connection with the execution of the collaboration agreement, we received an up-front payment of $165.0 million in July 2006. As of December 31, 2009, we had received $100.0 million of contingent milestone payments related to the development of telaprevir under the collaboration agreement. In addition, the agreement provides for additional contingent milestone payments to us of up to $250.0 million related to the regulatory filing with and approval of telaprevir by the European Medicines Evaluation Agency, and the launch of telaprevir in the European Union. In the third quarter of 2009, we entered into two financial transactions related to these $250.0 million in potential future milestone payments, which are discussed in detail in the consolidated financial statements and management's discussion and analysis contained in this Annual Report on Form 10-K. In the first transaction, we issued a note in the amount of $155.0 million secured by the first $155.0 million of these milestone payments, and in the second transaction we sold our rights to the remaining $95.0 million in future milestone payments. Our collaboration agreement with Janssen was unchanged by these transactions.

        Janssen is responsible for 50% of drug development costs under the development program for North America and the Janssen territories. Each of the parties to the collaboration agreement will be responsible for drug supply in their respective territories. The collaboration agreement also includes a tiered royalty payable to us averaging in the mid-20% range, as a percentage of net sales in the Janssen territories, depending upon successful commercialization. In addition, Janssen will be responsible for certain third-party royalties in its territories. Janssen may terminate the collaboration agreement upon six months' notice to us. In such an event, all manufacturing, commercialization and intellectual property rights to telaprevir in the Janssen territories under the collaboration agreement will revert to us.

        As part of the collaboration agreement, following regulatory approval and commercialization of telaprevir in both North America and Janssen's territories, we have agreed to establish a global health initiative with Tibotec, with the goals of advancing the prevention, diagnosis, treatment and cure of HCV infection, which will be principally directed toward developing countries.

Mitsubishi Tanabe Pharma Corporation

        In June 2004, we entered into a collaboration agreement with Mitsubishi Tanabe pursuant to which Mitsubishi Tanabe agreed to provide financial and other support for the development and commercialization of telaprevir. Under the terms of the agreement, Mitsubishi Tanabe has the right to develop and commercialize telaprevir in Japan and specified other Far East countries. The original agreement provided for payments by Mitsubishi Tanabe to us through Phase 2 clinical development, including an up-front license fee, development stage milestone payments and reimbursement of certain drug development costs for telaprevir.

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        In July 2009, we amended the collaboration agreement with Mitsubishi Tanabe. Under the amended agreement, we received $105.0 million in the third quarter of 2009, and will be eligible to receive a further contingent milestone payment, which if realized would range between $15.0 million and $65.0 million. The amended agreement provides Mitsubishi Tanabe with a fully-paid license to commercialize telaprevir to treat HCV infection in Japan and specified other countries in the Far East, as well as the right to manufacture telaprevir for sale in its territory. Mitsubishi Tanabe is responsible for its own development and manufacturing costs in its territory. Mitsubishi Tanabe may terminate the agreement at any time without cause upon 60 days' prior written notice to us.

Cystic Fibrosis Foundation Therapeutics Incorporated

        In May 2004, we entered into a collaboration agreement with CFFT, the non-profit drug discovery and development affiliate of the Cystic Fibrosis Foundation, pursuant to which CFFT provided us with funding for our CF research and development programs, which funding was completed in 2008. Two drug candidates currently in clinical development for CF, VX-770 and VX-809, were discovered by us under this research collaboration. We retain the right to develop and commercialize any compounds discovered in the course of the research collaboration, including VX-770 and VX-809, and we will pay a royalty to CFFT on the net sales of any approved drugs discovered in the collaboration.

Merck & Co., Inc.

        In June 2004, we entered into a collaboration with Merck to discover, develop and commercialize Aurora kinase inhibitors. Under the agreement, Merck was responsible for developing and commercializing the drug candidates that resulted from the collaboration worldwide and would have paid us royalties on any product sales. Merck may terminate the agreement at any time without cause upon 90 days' advance written notice, except that a longer notice period is required in certain circumstances. Merck is conducting a Phase 1 clinical trial of MK-5108 (VX-689) involving patients with advanced and/or refractory tumors, but has indicated to us, based on its analysis of its broader portfolio of drug development programs, that it does not anticipate continuing further development activities with respect to MK-5108 after the completion of dosing of patients currently enrolled in this Phase 1 clinical trial. Merck is not conducting any other clinical trials of drug candidates that resulted from the collaboration.

GlaxoSmithKline plc

        In 1993, we entered into a collaboration with GlaxoSmithKline plc covering the research, development and commercialization of HIV protease inhibitors. The agreement provides that GlaxoSmithKline will pay us a royalty on all net sales of the HIV protease inhibitors covered by the agreement. In May 2008, we sold our right to receive future royalties from GlaxoSmithKline with respect to these HIV protease inhibitors, excluding the amount necessary to pay a third party a subroyalty on these net sales, for a one-time cash payment to us of $160.0 million.

INTELLECTUAL PROPERTY

        We actively seek protection for our products and proprietary information by means of United States and foreign patents, trademarks and copyrights, as appropriate. In addition, we rely upon trade secret protection and contractual arrangements to protect certain of our proprietary information and products. We have patents and pending patent applications that relate to potential drug targets, compounds we are developing to modulate those targets, methods of making or using those compounds and proprietary elements of our drug discovery platform.

        Much of our technology and many of our processes depend upon the knowledge, experience and skills of key scientific and technical personnel. To protect our rights to our proprietary know-how and

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technology, we require all employees, as well as our consultants and advisors when feasible, to enter into confidentiality agreements that require disclosure and assignment to us of ideas, developments, discoveries and inventions made by these employees, consultants and advisors in the course of their service to us.

        While we have numerous issued patents and pending patent applications in our patent portfolio, we believe that the patents and patent applications in the United States and the European Union that are the most important to our business are those that claim the composition-of-matter of drug candidates that have progressed at least into Phase 2 clinical trials. The following table sets forth the status of the primary patents and patent applications in the United States and the European Union covering the composition-of-matter of these drug candidates:

        We hold issued patents and pending patent applications in the United States, and in foreign countries we deem appropriate, claiming intellectual property developed as part of each of our significant research and development programs. In addition to the composition-of-matter patents and patent applications listed above, our intellectual property holdings include but are not limited to:

•

United States and foreign patents and patent applications covering telaprevir, VX-222, VX-759, VX-985 and other HCV protease and polymerase inhibitors and the use of these compounds to treat HCV infection.



•

United States and foreign patent applications covering potentiators and correctors of the CFTR protein, including VX-770 and VX-809 and many other related compounds, and the use of those potentiators and correctors to treat CF.



•

United States and foreign patents and patent applications covering inhibitors of a variety of kinase proteins, including VX-509, a JAK3 inhibitor.



•

United States and foreign patents and patent applications covering caspase-1 inhibitors, including VX-765.



•

United States and foreign patent applications covering the manufacture, pharmaceutical compositions, related solid forms, formulations, dosing regimens and methods of use of these compounds, including telaprevir and VX-770.

        We cannot be certain, however, that issued patents will be enforceable or provide adequate protection or that pending patent applications will result in issued patents

        From time to time we enter into non-exclusive license agreements for proprietary third-party technology used in connection with our research activities. These license agreements typically provide for the payment by us of a license fee, but may also include terms providing for milestone payments or royalties for the development and/or commercialization of our drug products arising from the related research.

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MANUFACTURING

Manufacturing Approach and Philosophy

        As we advance our proprietary drug candidates through clinical development toward commercialization, we will continue to build and maintain our supply chain and quality assurance resources. We rely on an international network of third parties to manufacture and distribute our drug candidates for clinical trials, and we expect that we will continue to rely on third parties for the foreseeable future to meet our commercial supply needs for any of our drug candidates that are approved for sale.

        Our supply chain for sourcing raw materials and manufacturing drug product ready for distribution is a multi-step international endeavor. Third-party contract manufacturers, including some in Asia, supply us with raw materials, and contract manufacturers in the European Union and the United States convert these raw materials into drug substance, and convert the drug substance into final dosage form. Establishing and managing this global supply chain requires a significant financial commitment and the creation and maintenance of numerous third-party contractual relationships.

        We are focusing resources on the development of systems and processes to track, monitor and oversee our third-party manufacturers' activities. We regularly evaluate the performance of our third-party manufacturers with the objective of confirming their continuing capabilities to meet our needs efficiently and economically. Manufacturing facilities, both foreign and domestic, are subject to inspections by or under the authority of the FDA and by or under the authority of other federal, state, local or foreign authorities. A failure by any of our third-party manufacturers to pass an inspection could adversely affect our ability to launch telaprevir or VX-770 in a timely manner, if we obtain marketing approval, or adversely affect our ability to continue to distribute telaprevir or VX-770 after launch.

        We have established a quality assurance program intended to ensure that our third-party manufacturers and service providers produce materials and provide services, when applicable, in accordance with the FDA's current Good Manufacturing Practices, or cGMP, and other applicable regulations.

Manufacture of Telaprevir Clinical and Commercial Supplies

        We require a supply of telaprevir for our clinical trials and have agreed to exercise our contractual rights from our third-party manufacturers to provide a supply of telaprevir to Janssen and Mitsubishi Tanabe for their clinical trials. We will require a supply of telaprevir for sale in North America if we obtain marketing approval and have agreed to exercise our contractual rights from our third-party manufacturers to provide, until April 2012, a supply of telaprevir drug substance to Mitsubishi Tanabe for their use in manufacturing final dosage telaprevir for sale, if approved, in its territory.

        We have completed the technical development work for our commercial formulation of telaprevir, established relationships with multiple third-party manufacturers for the manufacture of clinical and commercial supply of telaprevir, and completed contracts for our primary supply of drug substance, drug product and key raw materials. We are manufacturing telaprevir, through our third-party manufacturer network, to meet our, Janssen's and Mitsubishi Tanabe's clinical supply needs. We believe our past and continuing efforts to expand our relationships with third-party manufacturers and oversee their activities will be important to support a timely and effective commercial launch of telaprevir and its consistent supply in subsequent years.

        We have completed the transfer of technical information regarding the manufacture of telaprevir to Janssen so that Janssen will be able to manufacture telaprevir, if approved, for sale in Janssen's territories and as a secondary supply source of drug substance for us. While we believe there are multiple third parties capable of providing most of the materials and services we need in order to

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manufacture and distribute telaprevir, and that supply of materials that cannot be second-sourced can be managed with inventory planning, there is always a risk that we may underestimate demand, and that our manufacturing capacity through third-party manufacturers may not be sufficient. In addition, because of the significant lead times involved in our supply chain for telaprevir, we may have less flexibility to adjust our supply in response to changes in demand than if we had shorter lead times.

Manufacture of VX-770 Clinical and Commercial Supplies

        We require VX-770 for clinical trials in North America and Europe, and will require a supply of VX-770 for sale in North America and Europe if we obtain marketing approval. We obtain VX-770 to meet our clinical supply needs through a third-party manufacturer network and are focused on completing the technical development work required to produce VX-770 at a commercial scale. We are in the process of expanding our existing relationships with our third-party manufacturers and establishing new relationships with third-party manufacturers, in order to establish a supply chain for VX-770 to support the potential commercial launch of VX-770.

COMPETITION

        The pharmaceutical industry is characterized by extensive research efforts, rapid technological progress and intense competition. There are many public and private companies, including pharmaceutical companies, chemical companies and biotechnology companies, engaged in developing products for the same human therapeutic areas that we are targeting. Many of our competitors have substantially greater financial, technical and human resources than we do and are more experienced in the development of new drugs than we are. In order for us to compete successfully, we may need to demonstrate improved safety, efficacy, ease of manufacturing and market acceptance of our products relative to our competitors' products that have received or will receive regulatory approval for marketing.

        We face competition based on the safety and efficacy of our drug candidates, the timing and scope of regulatory approvals, the availability and cost of supply, marketing and sales capabilities, reimbursement coverage, price, patent protection and other factors. Our competitors may develop or commercialize more effective, safer or more affordable products than we are able to develop or commercialize or obtain more effective patent protection. As a result, our competitors may commercialize products more rapidly or effectively than we do, which would adversely affect our competitive position, the likelihood that our drug candidates, if approved, would achieve initial market acceptance and our ability to generate meaningful revenues from those drugs. Even if our drug candidates are approved and achieve initial market acceptance, competitive products may render our drugs obsolete or noncompetitive. If any such drug is rendered obsolete, we may not be able to recover the expenses of developing, stockpiling and commercializing that drug. With respect to all of our drugs and drug candidates, we are aware of existing treatments and numerous drug candidates in development by our competitors.

HCV Infection

Current HCV Market

        A 48 week course of both peg-IFN, which requires weekly injections, and RBV, which is an oral drug, is the current standard treatment for genotype 1 HCV infection. This treatment regimen is associated with significant side-effects, including fatigue, flu-like symptoms, rash, depression and anemia. A significant portion of patients who begin treatment do not achieve an SVR. Based on discussions with physicians who treat patients infected with HCV, we believe that there are a significant number of patients with HCV who have been diagnosed but not yet achieved an SVR that may consider treatment with new therapies that are more effective.

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Initial Anticipated Competitive Landscape

        While we are aware of numerous companies that are developing potentially competitive drug candidates, Merck's (previously Schering-Plough's) protease inhibitor, boceprevir, is the only protease inhibitor that is being developed on a timeline comparable to telaprevir. Merck is conducting Phase 3 clinical trials of boceprevir and has indicated that it expects to submit an NDA for boceprevir in 2010, which would put it on a timeline to potentially launch boceprevir in 2011. Merck's Phase 3 clinical trials include a clinical trial that enrolled approximately 404 treatment-failure patients but excluded null responders to prior treatment and a Phase 3 clinical trial involving approximately 1,100 treatment-naïve patients with genotype 1 HCV infection. In November 2009, Merck initiated another Phase 3 clinical trial for boceprevir that it estimates will enroll approximately 660 patients infected with genotype 1 HCV to compare the effect on efficacy of erythropoietin use versus reducing the dose of RBV for the management of anemia.

        If telaprevir and boceprevir are both approved on a comparable timeline, we believe that the drugs would compete in the marketplace based on, among other things, safety and efficacy data from their respective clinical trials, breadth of approved use, dosing regimen, cost, cost of co-therapies and side-effect profiles.

Long-term Competitive Landscape

        We are aware of numerous other compounds in clinical trials that target HCV infection through a number of different mechanisms of action, and we believe that there are many additional potential HCV treatments in research or early development. There are a number of earlier-stage protease inhibitors, HCV polymerase inhibitors and HCV NS5A inhibitors, each of which is a specifically targeted anti-viral compound. We believe that these earlier-stage drug candidates, if approved, would be launched several years after telaprevir. If any of these drug candidates is approved as a treatment for HCV infection, we expect that such drug candidates would compete with telaprevir on the basis of the factors described above.

        Future competition in the HCV treatment market may result from the administration of combinations of new oral therapies, and we are aware of a number of companies focusing on developing combinations of specifically-targeted antiviral compounds. We are planning a Phase 2a clinical trial to evaluate a combination of VX-222, our lead polymerase inhibitor, and telaprevir with and without peg-IFN and RBV. We also are aware that Bristol-Myers Squibb Company is conducting Phase 2 clinical trials of an NS5A inhibitor it is developing in combination with a protease inhibitor it is developing, and Intermune, Inc. and Pharmasset, Inc., in collaboration with Roche, are evaluating a combination of a protease inhibitor being developed by Intermune and a polymerase inhibitor being developed by Pharmasset.

CF

        Several companies are engaged in the process of developing treatments for CF, including a limited number of drug candidates that are designed to improve the function of CFTR proteins, and a number of antibiotics and anti-inflammatory drug candidates. PTC Therapeutics, Inc. is evaluating ataluren, which was formerly known as PTC124, in a Phase 3 clinical trial in patients with CF. Ataluren is a drug candidate designed to improve the production of CFTR proteins in patients with nonsense genetic mutations that halt the production of CFTR proteins before the protein is fully formed. Inspire Pharmaceuticals Inc. is conducting Phase 3 clinical trials of denufosol tetrasodium, an inhaled molecule designed to stimulate chloride and liquid secretions in the airways of patients with CF.

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GOVERNMENT REGULATION

        The research, development, testing, manufacture, quality control, approval, labeling, packaging, storage, record keeping, promotion, advertising, distribution and marketing of the drug candidates that we are developing are subject to extensive regulation by United States and foreign governmental authorities. In particular, pharmaceutical products are subject to rigorous preclinical, nonclinical and clinical testing and other approval requirements by the FDA in the United States under the Federal Food, Drug and Cosmetic Act, and by comparable agencies in most foreign countries. In addition to prohibiting the sale and distribution of pharmaceutical products prior to regulatory approval, the FDA and comparable agencies in most foreign countries prohibit the pre-approval promotion of investigational drugs. We have summarized the FDA process below, but other countries may have different approval processes with which we or our collaborators will need to comply if we seek to conduct clinical trials or obtain marketing approval in those countries. In addition, even if we ultimately intend to seek initial marketing approval in the United States, we may conduct early clinical trials in other countries, for a variety of reasons, and therefore the submission of our initial investigational new drug, or IND, application in the United States might not occur until after one or more foreign-sited clinical trials have been initiated.

FDA Approval Process

        As an initial step in the FDA regulatory review process, toxicity studies in animals and other nonclinical studies typically are conducted to help identify potential safety problems that might be associated with administration of the drug candidate being tested. For certain diseases, animal models exist that are believed to be predictive of efficacy in humans. For such diseases, a drug candidate typically is tested for efficacy in that animal model. The results of these initial animal safety and disease model studies are submitted to the FDA as a part of the IND submission, prior to commencement of human clinical trials in the United States. For several of our drug candidates, no appropriately predictive animal model exists. As a result, no in vivo evidence of efficacy will be available until those drug candidates progress to human clinical trials. A variety of nonclinical studies in a number of animal species, and other nonclinical studies, ordinarily are conducted while human clinical trials are underway, to provide supplemental toxicology and other information. This information as well as the results from the early clinical trials provide a foundation for the design of broader and more lengthy human clinical trials.

        Clinical trials typically are conducted in three sequential phases, although the phases may overlap. Phase 1 frequently begins with the initial introduction of the drug candidate into healthy human subjects prior to introduction into patients. The drug candidate may then be tested in a relatively small number of patients for preliminary information, dosage tolerance, absorption, metabolism, excretion, clinical pharmacology and, if possible, for early information on efficacy. Phase 2 typically involves trials in a small sample of the intended patient population to assess the efficacy of the drug for a specific indication, to determine dose tolerance and the optimal dose range and to gather additional information relating to safety and potential adverse effects. Phase 3 trials are undertaken to further evaluate clinical safety and efficacy in an expanded patient population at geographically dispersed trial sites, to obtain information on the overall risk-benefit ratio of the drug candidate and to provide an adequate basis for proposed labeling. Each trial is conducted in accordance with standards set forth in a protocol that details the design and objectives of the trial, the parameters to be used to monitor safety and the efficacy criteria to be evaluated. For clinical trials in the United States, each protocol must be submitted to the FDA to supplement the original IND submission. Further, each clinical trial must be evaluated by an independent Institutional Review Board, or IRB, which evaluates clinical research at or for each institution at which the trial will be conducted. The IRBs will consider, among other things, ethical factors and the safety of human subjects in the proposed trials.

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        Data from nonclinical testing and all clinical trials, along with descriptions of the manufacturing process, analytical tests, proposed labeling and the proposed risk evaluation and mitigation strategies and other relevant information, are submitted to the FDA as part of requesting approval to market the drug in the NDA. The process of completing nonclinical and clinical testing, submitting the NDA and obtaining FDA approval for a new drug is likely to take a number of years and require the expenditure of substantial resources. Preparing an NDA involves extensive data collection, verification, analysis and expense, and there can be no assurance that approval of the drug candidate that is the subject of a particular NDA will be granted on a timely basis, if at all. The FDA reviews all NDAs to ensure that they are sufficiently complete for substantive review before it accepts them for filing. The approval process is affected by a number of factors, including the severity of the targeted disease, the availability of alternative treatments and the risks and benefits demonstrated in clinical trials. The FDA may deny an NDA if applicable regulatory criteria are not satisfied or may require additional testing or information. Among the conditions for marketing approval is the requirement that the prospective manufacturer's quality control and manufacturing procedures conform to the FDA's cGMP regulations, which must be followed at all times. In complying with standards set forth in these regulations, manufacturers must continue to expend time, money and effort in the area of production and quality control to ensure full compliance. Manufacturing facilities, both foreign and domestic, also are subject to inspections by the FDA and by other federal, state, local agencies or foreign authorities. In addition, the company developing a drug candidate typically must submit a plan setting forth its risk evaluation and mitigation strategies.

        Under the FDA Modernization Act of 1997, the FDA may grant "Fast Track" designation to facilitate the development of a drug intended for the treatment of a serious or life-threatening condition if the drug demonstrates, among other things, the potential to address an unmet medical need. The benefits of Fast Track designation include scheduled meetings with the FDA to receive input on development plans, the option of submitting an NDA in sections rather than submitting all sections simultaneously, and the option of requesting evaluation of trials using surrogate endpoints. Fast Track designation does not necessarily lead to a priority review or accelerated approval of a drug candidate by the FDA. Telaprevir and VX-770 have received Fast Track designation by the FDA.

Timing to Approval

        We estimate that it generally takes 10 to 15 years, or possibly longer, to discover, develop and bring to market a new pharmaceutical product in the United States as outlined below:

        A drug candidate may fail to progress at any point during this process. Animal and other nonclinical studies typically are conducted during each phase of human clinical trials.

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Patent Term Restoration

        Pursuant to the Drug Price Competition and Patent Term Restoration Act of 1984, referred to as the Hatch-Waxman Amendments, some of our patents, under certain conditions, may be eligible for limited patent term extension for a period of up to five years as compensation for patent term lost during drug development and the FDA regulatory review process. However, this extension period cannot be extended beyond 14 years from the drug's approval date. The patent term restoration period is generally one-half the period of time elapsed between the effective date of an IND application and the submission date of an NDA, plus the period of time between the submission date of the NDA and FDA approval. The United States Patent and Trademark Office, in consultation with the FDA, reviews and approves applications for any patent term extension or restoration. We intend to seek the benefits of this statute, but there can be no assurance that we will be able to obtain any such benefits.

Orphan Drug Designation

        Under the Orphan Drug Act, the FDA may grant orphan drug designation to drugs intended to treat a "rare disease or condition" that affects fewer than 200,000 individuals in the United States. Orphan drug designation must be requested before submitting an NDA. Orphan drug designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process. If a drug that has an orphan drug designation subsequently receives the first FDA approval for the indication for which it has such designation, the product is entitled to orphan exclusivity, which means the FDA may not approve any other application to market the same drug for the same indication for a period of seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan exclusivity. Nevertheless, competitors may receive approval of different drugs or biologics for the indications for which the orphan product has exclusivity. VX-770 has been granted orphan drug designation.

Post-approval Studies

        Even after FDA approval has been obtained, further studies, including post-approval trials, may be required to provide additional data on safety and will be required to gain approval for the sale of a drug as a treatment for clinical indications other than those for which the drug initially was approved. Also, the FDA will require post-approval reporting to monitor the side-effects of the drug. Results of post-approval programs may limit or expand the indications for which the drug may be marketed. Further, if there are any requests for modifications to the initial FDA approval for the drug, including changes in indication, manufacturing process, labeling or manufacturing facilities, submission of a supplemental NDA to the FDA may be required.

Reimbursement

        Sales of drugs depend in significant part on the availability of third-party reimbursement. Third-party payors include government health administrative authorities, managed care providers, private health insurers and other organizations. We anticipate third-party payors will provide reimbursement for our drugs if we are successful in obtaining marketing approval. However, third-party payors are increasingly challenging pricing, and in some cases, examining the cost-effectiveness of drugs. In the future, we may need to conduct expensive pharmacoeconomic studies for some of our drug candidates in order to demonstrate their cost-effectiveness, if we successfully obtain marketing approval. The process of seeking reimbursement from third-party payors in the future may be time-consuming and expensive.

        The Medicare Prescription Drug Improvement and Modernization Act of 2003, or the MMA, extended a prescription drug benefit to Medicare beneficiaries and imposed requirements for the distribution and pricing of prescription drugs under Medicare Part D. Unlike other Medicare benefits,

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the drug benefit available under Part D is not standardized and there is no guarantee that any drug for which we obtain approval will be covered under Part D.

        We expect that there may continue to be a number of federal and state proposals to implement governmental pricing controls and limit the growth of health care costs, including the cost of prescription drugs. At the present time, Medicare is prohibited from negotiating directly with pharmaceutical companies for drugs. However, Congress is considering passing legislation that would lift the ban on federal negotiations.

        In addition, in some foreign countries, the proposed pricing for a drug must be approved before it may be marketed lawfully. The requirements governing drug pricing vary widely from country to country. For example, the European Union provides options for its member states to restrict the range of medicinal products for which their national health insurance systems provide reimbursement and to control the prices of medicinal products for human use. A member state may approve a specific price for the medicinal product or it may instead adopt a system of direct or indirect controls on the profitability of the company placing the medicinal product on the market.

Foreign Regulation

        In addition to regulations in the United States, we and our collaborators are and will be subject to a variety of foreign regulations governing clinical trials and commercial sales and distribution of drugs. Whether or not we obtain FDA approval for a drug, approval of a drug candidate by the comparable regulatory authorities of foreign countries must be obtained before we or our collaborators can commence clinical trials or marketing of the drug in those countries. The approval process varies from country to country and the time may be longer or shorter than that required for FDA approval. The requirements governing the conduct of clinical trials, product licensing, pricing and reimbursement vary greatly from country to country.

        Under European Union regulatory systems, marketing authorization applications may be submitted either under a centralized or decentralized procedure. The centralized procedure, which is compulsory for medicines produced by certain biotechnological processes and optional for those that are highly innovative, provides for the grant of a single marketing authorization that is valid for all European Union member states. For drugs without approval in any European Union member state, the decentralized procedure provides for assessment of a marketing application by one member state, known as the reference member state, and review and possible approval of that assessment by one or more other, or concerned, member states. Under this procedure, an applicant submits an application, or dossier, and related materials—draft summary of product characteristics, draft labeling and package leaflet—to the reference member state and concerned member states. The reference member state prepares a draft assessment and drafts of the related materials within 120 days after receipt of a valid application. Within 90 days of receiving the reference member state's assessment report, each concerned member state must decide whether to approve the assessment report and related materials. If a member state cannot approve the assessment report and related materials on the grounds of potential serious risk to public health, the disputed points may eventually be referred to the European Commission, whose decision is binding on all member states of the European Union.

Other Regulations

        Pharmaceutical companies also are subject to various federal and state laws pertaining to health care "fraud and abuse," including anti-kickback laws and false claims laws. Anti-kickback laws make it illegal for any entity or person to solicit, offer, receive or pay any remuneration in exchange for or to induce the referral of business, including the purchase or prescription of a particular drug. False claims laws prohibit anyone from knowingly and willingly presenting to third-party payors including Medicare and Medicaid, or causing to be presented, for payment claims for reimbursed drugs or services that are

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false or fraudulent, claims for items or services not provided as claimed or claims for medically unnecessary items or services.

        In addition to the statutes and regulations described above, we also are subject to regulation under the Occupational Safety and Health Act, the Environmental Protection Act, the Toxic Substances Control Act, the Resource Conservation and Recovery Act and other federal, state, local and foreign statutes and regulations, now or hereafter in effect.

EMPLOYEES

        As of December 31, 2009, we had 1,432 employees (1,422 full-time, 10 part-time). The number of our full-time employees increased by 6% during 2009, from 1,339 on December 31, 2008. We are likely to further increase our headcount in 2010 as we invest in expanding our commercialization capabilities. Of our employees, 1,119 were based in Massachusetts, 177 were based in California, 103 were based in Europe and 33 were based in Canada. Our scientific staff members have diversified experience and expertise in molecular and cell biology, biochemistry, synthetic organic chemistry, protein X-ray crystallography, protein nuclear magnetic resonance spectroscopy, microbiology, computational chemistry, biophysical chemistry, medicinal chemistry, clinical pharmacology and clinical medicine. Our clinical development personnel have extensive expertise in designing and executing clinical trials, and we are building our commercialization organization. Our employees are not covered by a collective bargaining agreement, and we consider our relations with our employees to be good.

OTHER MATTERS

Information Available on the Internet

        Our internet address is www.vrtx.com. Our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and all amendments to those reports, are available to you free of charge through the "Finances/Investor Info-SEC Filings" section of our website as soon as reasonably practicable after those materials have been electronically filed with, or furnished to, the Securities and Exchange Commission.

Corporate Information

        Vertex was incorporated in Massachusetts in 1989, and our principal executive offices are located at 130 Waverly Street, Cambridge, Massachusetts 02139. We have research sites located in San Diego, California; Coralville, Iowa; Montreal, Canada and Milton Park, U.K. We also have an office in Washington, D.C.

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EXECUTIVE OFFICERS AND DIRECTORS

        The names, ages and positions held by our executive officers and directors are as follows:

        Mr. Emmens has been our Chairman, Chief Executive Officer and President since May 2009. He has been a member of our Board of Directors since 2004 and became our President in February 2009. Mr. Emmens is the Chairman of the Board of Directors of Shire plc, a specialty biopharmaceutical company, and has been a member of Shire's board since March 2003. From March 2003 to June 2008, Mr. Emmens was also the Chief Executive Officer of Shire plc, which had more than 2,500 employees and revenues of $1.8 billion in 2006. Before joining Shire in 2003, Mr. Emmens served as President of Merck KGaA's global prescription pharmaceuticals business in Darmstadt, Germany. In 1999, he joined Merck KGaA and established EMD Pharmaceuticals, Inc., its United States prescription pharmaceutical business. Mr. Emmens held the position of President and Chief Executive Officer at EMD Pharmaceuticals from 1999 to 2001. Prior to this, Mr. Emmens held various positions, including Chief Executive Officer, at Astra Merck, Inc. as well as several positions at Merck & Co., Inc. Mr. Emmens was a member of the Board of Directors of Incyte Corporation from 2006 through February 2009. Mr. Emmens received a B.S. degree in business management from Farleigh Dickinson University.

        Dr. Mueller is our Executive Vice President, Global Research and Development, a position he has held since May 2009, and has been our Chief Scientific Officer since July 2003. Dr. Mueller was our Executive Vice President, Drug Innovation and Realization, from February 2006 to May 2009, and our Senior Vice President, Drug Discovery and Innovation, from July 2003 to February 2006. Prior to joining us, Dr. Mueller was the Senior Vice President, Research and Development, of Boehringer Ingelheim Pharmaceuticals, Inc., with responsibility for the development of all drug candidates in the

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company's worldwide portfolio in North America. He led research programs in the areas of immunology, inflammatory cardiovascular disease and gene therapy on a global basis. During his time with Boehringer Ingelheim, Dr. Mueller oversaw the discovery of numerous development candidates and held several positions in basic research, medicinal chemistry and management. Dr. Mueller received both an undergraduate degree and a Ph.D. in chemistry at the Albert Einstein University of Ulm, Germany, where he also holds a Professorship in Theoretic Organic Chemistry. He completed fellowships in quantum pharmacology at Oxford University and in biophysics at Rochester University.

        Mr. Smith is our Executive Vice President and Chief Financial Officer, a position he has held since February 2006. From November 2003 to February 2006, he was our Senior Vice President and Chief Financial Officer, and from October 2001 to November 2003, he served as our Vice President and Chief Financial Officer. Prior to joining us, Mr. Smith served as a partner in the Life Science and Technology Practice Group of Ernst & Young LLP, an accounting firm, from 1999 to 2001. Mr. Smith initially joined Ernst & Young's U.K. firm in 1987, and then joined its Boston office in 1995. Mr. Smith currently is a member of the Boards of Directors of Acorda Therapeutics, Inc., Infinity Pharmaceuticals, Inc. and TolerRx Inc. Mr. Smith holds a B.A. in accounting and finance from Manchester Metropolitan University, U.K., is a member of the American Institute of Certified Public Accountants and is a Chartered Accountant of England and Wales.

        Ms. Wysenski is our Executive Vice President and Chief Commercial Officer, a position she has held since December 2009. Prior to joining us, Ms. Wysenski held the position of Chief Operating Officer of Endo Pharmaceuticals, a 1,200-person specialty pharmaceutical company, where she led sales, marketing, commercial operations, supply chain management, human resources and various business development initiatives. Prior to her role at Endo, Ms. Wysenski participated in the establishment of EMD Pharmaceuticals, Inc., where she held various leadership positions, including the role of President and Chief Executive Officer from 2001 to 2006 and Vice President of Commercial from 1999 to 2001. From 1984 to 1998, Ms. Wysenski held several sales-focused roles at major pharmaceutical companies, including Vice President of Field Sales for Astra Merck, Inc. Ms. Wysenski serves on the North Carolina Central University Board of Trustees and is a founder of the Research Triangle Park chapter of the Healthcare Business Women's Association. Ms. Wysenski holds a B.S. from Kent State University and an Executive Masters in Business Administration from Baldwin Wallace College.

        Mr. Kenneth Boger is our Senior Vice President and General Counsel, a position he has held since joining us in 2001. He came to us from the law firm of Kirkpatrick & Lockhart LLP, now known as K&L Gates, where he was a partner specializing in business and corporate law and was a member of the firm's Management Committee. Prior to the merger of Kirkpatrick & Lockhart with the Boston law firm of Warner & Stackpole LLP in 1999, Mr. Boger was a partner at Warner & Stackpole, where he served on its Executive Committee from 1988 to 1997. Mr. Boger holds an A.B. in history from Duke University, an M.B.A. from the Graduate School of Business at the University of Chicago, and a J.D. from Boston College Law School. Mr. Boger is the brother of Dr. Joshua Boger, one of our directors.

        Ms. Kelly-Croswell is our Senior Vice President, Human Resources, a position she has held since July 2007. Ms. Kelly-Croswell served as our Vice President, Human Resources from July 2006 through June 2007. From November 2005 through June 2006, Ms. Kelly-Croswell served as Vice President of Human Resources of NitroMed, Inc., a pharmaceutical company. From February 2004 to November 2005, Ms. Kelly-Croswell served as Senior Vice President, Human Resources, for the Health Care Division and Service Operations, of CIGNA, an employee benefits company. From September 2001 to February 2004, Ms. Kelly-Croswell served as Vice President of Human Resources for Global Research and Development for the Monsanto Company, an agricultural products and solutions company that she joined in 1998. Ms. Kelly-Croswell holds a B.S. in Finance and an M.A. in Labor and Industrial Relations from the University of Illinois at Urbana-Champaign.

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        Mr. Sachdev is our Senior Vice President, Corporate Affairs and Public Policy, a position he has held since he joined us in July 2007. Mr. Sachdev served as Executive Vice President, Health of the Biotechnology Industry Organization (BIO) from April 2005 through June 2007. At BIO, he was the senior executive responsible for managing BIO's Health Section and its Governing Board, and for directing all health care policy and execution. Mr. Sachdev was the Deputy Commissioner for Policy at the FDA from April 2004 through April 2005, and held several other senior positions within the FDA from September 2002 through April 2004. From 1998 to 2002, Mr. Sachdev served as Majority Counsel to the Committee on Energy and Commerce in the U.S. House of Representatives, where he was responsible for bioterrorism, food safety and environmental issues. From 1993 to 1997, Mr. Sachdev practiced law, first at the Chemical Manufacturers Association, and then with the law firm of Ropes & Gray. Mr. Sachdev holds a B.S from Carnegie Mellon University, and a J.D. from Emory University School of Law.

        Mr. Silva is our Vice President and Corporate Controller, a position he has held since September 2008. Mr. Silva joined us in August 2007 as Senior Director, Accounting Operations. Prior to joining us, he was the Vice President, Internal Reporting at Iron Mountain Incorporated from July 2006 until August 2007 and a consultant to Iron Mountain's financing department from April 2005 until July 2006. He was the Finance Director of the Bioscience Technologies Division of Thermo Electron Corporation from 2002 to April 2005. Mr. Silva holds a B.S. in accounting from Assumption College.

        Dr. Sanders has been a member of our Board of Directors since 1996 and has been our lead outside director since May 2009. Dr. Sanders served as our Chairman from May 2006 through May 2009 and was our lead outside director from 2003 through May 2006. He retired in 1994 as Chief Executive Officer and in 1995 as Chairman of Glaxo Inc. From 1990 to 1995, he served as a member of the board of Glaxo plc. From 1981 to 1989, Dr. Sanders held a number of positions at Squibb Corporation, including that of Vice Chairman. He is currently a director of Biodel Inc., Biocryst Pharmaceuticals Inc., Cephalon, Inc., and Icagen, Inc. Dr. Sanders was a member of the Board of Directors of Genentech, Inc. from 1999 through its acquisition by Roche in March 2009, Fisher Scientific International from 2004 through its merger in November 2006, BioPure Corporation from 1997 through 2007 and Trimeris, Inc. from 1996 through 2006. Dr. Sanders also has served in the past on the boards of Merrill Lynch, Reynolds Metals Co. and Morton International Inc. Dr. Sanders had his undergraduate education at the University of Texas, and earned an M.D. from the University of Texas Southwestern Medical School.

        Dr. Joshua Boger is the founder of Vertex and has been a director since our inception in 1989. He was our Chief Executive Officer from 1992 through May 2009. He was our Chairman of the Board from 1997 until May 2006 and our President from our inception until December 2000, and from 2005 through February 2009. He was our Chief Scientific Officer from 1989 until May 1992. Prior to founding Vertex in 1989, Dr. Boger held the position of Senior Director of Basic Chemistry at Merck Sharp & Dohme Research Laboratories in Rahway, New Jersey, where he headed both the Department of Medicinal Chemistry of Immunology & Inflammation and the Department of Biophysical Chemistry. Dr. Boger holds a B.A. in chemistry and philosophy from Wesleyan University and M.S. and Ph.D. degrees in chemistry from Harvard University. Dr. Boger is the brother of Mr. Kenneth Boger, our Senior Vice President and General Counsel.

        Dr. Brimblecombe has been a member of our Board of Directors since 1993 and a member of the Board of Vertex Pharmaceuticals (Europe) Ltd. since 2005. He served as Chairman of Vanguard Medica plc from 1991 to 2000, of Core Group plc from 1997 to 1999, of Oxford Asymmetry International plc from 1997 to 2000 and pSivida Ltd. from 2002 to 2007. From 1979 to 1990, he held various Vice Presidential posts in SmithKline & French Laboratories' research and development organization, including Vice President R&D for Europe and Japan. He is currently an advisor to MVM Life Science Partners LLP, a venture capital firm. He holds Ph.D. and D.Sc. degrees in pharmacology from the University of Bristol, England.

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        Dr. Collinson has been a member of our Board of Directors since July 2001. He currently serves as a Partner at Forward Ventures, a venture capital firm. Prior to our acquisition of Aurora Biosciences Corporation in 2001, Dr. Collinson served as the President, Chief Executive Officer and Chairman of the Board of Aurora. Dr. Collinson held senior management positions with Glaxo Wellcome from December 1994 to June 1998, most recently serving as Co-Chairman, Hospital and Critical Care Therapy Management Team and Director of Hospital and Critical Care. Dr. Collinson received his Ph.D. in physical chemistry from the University of Oxford, England and his M.B.A. from Harvard University.

        Dr. Cordes has been a member of our Board of Directors since 2005, and a scientific advisor to us since 1996. Dr. Cordes was the Chairman of Vitae Pharmaceuticals, Inc., a position he held from January 2002 to March 2006. Prior to joining Vitae Pharmaceuticals, Dr. Cordes was a professor of pharmacy at the University of Michigan. Dr. Cordes received a B.S. degree in chemistry from the California Institute of Technology and a Ph.D. in biochemistry from Brandeis University.

        Dr. Leiden has been a member of our Board of Directors since July 2009. He has more than 20 years of experience in the biomedical and pharmaceutical sectors. Dr. Leiden was President and Chief Operating Officer of Abbott Laboratories, Pharmaceuticals Products Group, and a member of the Board of Directors of Abbott Laboratories from 2001 to 2006. From 1987 to 2000, Dr. Leiden held several academic appointments, including the Rawson Professor of Medicine and Pathology and Chief of Cardiology and Director of the Cardiovascular Research Institute at the University of Chicago, the Elkan R. Blout Professor of Biological Sciences at the Harvard School of Public Health, and Professor of Medicine at Harvard Medical School. He is an elected member of both the American Academy of Arts and Sciences, and the Institute of Medicine of the National Academy of Sciences. Dr. Leiden is currently a Managing Director at Clarus Ventures, a life sciences venture capital firm he joined in 2006. Dr. Leiden is also currently a director and the non-executive Vice Chairman of the board of Shire plc, and a director of several private biotechnology companies. Dr. Leiden was a member of the Board of Directors of Millennium Pharmaceuticals, Inc. from October 2007 until it was acquired in June 2008. Dr. Leiden received both his M.D. and Ph.D. degrees from the University of Chicago.

        Mr. Sachs has been a member of our Board of Directors since 1998. He is a General Partner at Charles River Ventures, a venture capital firm he joined in 1999. From 1998 to 1999, he served as Executive Vice President and General Manager of Ascend Communications, Inc. From 1997 until 1998, Mr. Sachs served as President and Chief Executive Officer of Stratus Computer, Inc. From 1995 to 1997, he served as Executive Vice President and General Manager of the Internet Telecom Business Group at Bay Networks, Inc. From 1993 to 1995, he served as President and Chief Executive Officer at Xylogics, Inc. Mr. Sachs was a director of BigBand Networks, Inc. from 2005 through June 2009. Mr. Sachs holds a B.S.E.E. in electrical engineering from Bucknell University, an M.E.E. in electrical engineering from Cornell University, and an M.B.A. from Northeastern University.

        Ms. Ullian has been a member of our Board of Directors since 1997. From 1996 through January 2010, she served as President and Chief Executive Officer of Boston Medical Center, a private, not-for-profit, 626-bed, academic medical center with a community-based focus. From 1994 to 1996, she served as President and Chief Executive Officer of Boston University Medical Center Hospital. From 1987 to 1994, Ms. Ullian served as President and Chief Executive Officer of Faulkner Hospital. She also serves as a director of Thermo Fisher Scientific Inc. and Hologic, Inc. In addition, Ms. Ullian was a member of the Board of Directors of Valeant Pharmaceuticals, Inc. during 2005 through 2007. Ms. Ullian holds a B.A. in political science from Tufts University and an M.P.H. from the University of Michigan.

        Mr. Winger has been a member of our Board of Directors since July 2009. Mr. Winger has over 30 years of experience as a financial executive, the majority of which has focused on the life sciences industry. He retired in 2008 from Applera Corporation, a life sciences company, where he had been

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Senior Vice President and Chief Financial Officer since 1997. He was previously Senior Vice President of Finance and Administration, and Chief Financial Officer at Chiron Corporation. Before joining Chiron, Mr. Winger held various financial executive positions, including Chief Financial Officer of The Cooper Companies, Inc. Mr. Winger is currently a director of the following public companies: Accuray Incorporated; Cephalon Inc.; and Nektar Therapeutics. In addition, Mr. Winger was a member of the Board of Directors of A.P. Pharma, Inc. during 2005 and 2006 and a member of the Board of Directors of Cell Genesys, Inc. until its merger with BioSante Pharmaceuticals in October 2009. He holds an M.B.A. from Columbia University Graduate School of Business and he earned his undergraduate degree from Siena College.

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ITEM 1A.    RISK FACTORS

RISK FACTORS

        Investing in our common stock involves a high degree of risk, and you should carefully consider the risks and uncertainties described below in addition to the other information included or incorporated by reference in this Annual Report on Form 10-K. If any of the following risks or uncertainties actually occurs, our business, financial condition or results of operations would likely suffer, possibly materially. In that case, the trading price of our common stock could decline.

Risks Related to Our Business

We expect to incur future losses, and we may never become profitable.

        We have incurred significant operating losses each year since our inception, including net losses of $642.2 million, $459.9 million and $391.3 million during the years ended December 31, 2009, 2008 and 2007, respectively, and expect to incur significant operating losses in 2010. We expect to continue to incur operating losses at least until we are able to obtain approval for and successfully commercialize telaprevir, because we are continuing to invest significant amounts in the late-stage development of telaprevir and VX-770, and in clinical development of our earlier-stage drug candidates and research activities. As a result, we believe that it is likely that our expenses will exceed our revenues at least until we begin receiving substantial product revenues. There can be no assurance that any of our drug candidates will be approved or, if approved, will be commercially successful. Our net losses have had and will continue to have an adverse effect on, among other things, our stockholders' equity, total assets and working capital. We expect that losses will fluctuate from quarter to quarter and year to year, and that such fluctuations may be substantial. We cannot provide assurance that we will ever become profitable.

We depend heavily on the success of our lead drug candidate, telaprevir, which is still being evaluated in a registration program. If we are unable to commercialize telaprevir, or experience delays in doing so, our business will be materially harmed.

        We are investing a substantial portion of our personnel and financial resources in the development of telaprevir, and we believe that a significant portion of the value attributed to our company by investors relates to the commercial potential of telaprevir. We expect that we will be making significant additional investments in telaprevir in order to be prepared for the potential commercial launch of telaprevir in the United States in 2011, including the establishment of a sales force and marketing capabilities and additional investment in commercial inventory. The clinical development and commercial success of telaprevir will depend on many factors, including the following:

•

successful completion of clinical trials with favorable outcomes relative to current standards of care and future competitive therapies;



•

receipt and timing of marketing approvals for telaprevir from the FDA and comparable foreign regulatory authorities;



•

receipt and timing of marketing approvals from the FDA and comparable foreign regulatory authorities for products being developed for the treatment of HCV infection by our competitors, including Merck's boceprevir;



•

additional discussions with the FDA and similar foreign authorities regarding the quality of our manufacturing process for telaprevir and our clinical trial results, including the results we expect to obtain in the second and third quarters of 2010 from our Phase 3 clinical trials of telaprevir;

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•

interactions with regulatory authorities regarding the contents of any NDA submission, including the data from our clinical trials and nonclinical studies, any plan setting forth risk evaluation and mitigation strategies and our manufacturing processes;



•

maintaining commercial manufacturing arrangements for telaprevir with third-party manufacturers that are subject to extensive regulation by the FDA, and successfully monitoring those manufacturing operations to ensure they meet our standards and those of regulatory authorities, including the FDA, that extensively monitor pharmaceutical manufacturing facilities;



•

our ability to establish telaprevir, if approved, as a significant component of any oral combination therapies that may be approved as a treatment for HCV infection;



•

the efficacy and other characteristics, including the side-effect profile, of telaprevir relative to existing and future treatments for HCV infection;



•

the effect of new health care legislation currently being considered in the United States;



•

our ability to increase awareness of the benefits of early treatment for HCV infection if telaprevir is approved, and to increase the rates of diagnosis of currently undiagnosed patients with HCV infection; and



•

the acceptance of telaprevir by patients, the medical community and with third-party payors.

        If the data from our ongoing clinical trials or nonclinical studies regarding the safety or efficacy of telaprevir are not favorable, we may be forced to delay or terminate the clinical development of telaprevir, which would materially harm our business. Further, even if we gain marketing approvals from the FDA and comparable foreign regulatory authorities in a timely manner, we cannot be sure that telaprevir will be commercially successful in the pharmaceutical market. If the results of clinical trials of telaprevir, the anticipated or actual timing of marketing approvals for telaprevir, or the market acceptance of telaprevir, if approved, including treatment reimbursement levels agreed to by third-party payors, do not meet the expectations of investors or public market analysts, the market price of our common stock would likely decline.

All of our drug candidates remain subject to clinical testing and regulatory approval. If we are unable to successfully develop and test our drug candidates, we will not be successful.

        The success of our business depends primarily upon our ability, and the ability of our collaborators, if any, to develop and commercialize our drug candidates, including telaprevir and VX-770, successfully. Due to the development efforts of our competitors, in order to be successful in a therapeutic area it is often necessary to develop follow-on compounds and/or new combination therapies. Our drug candidates are in various stages of development and must satisfy rigorous standards of safety and efficacy before they can be approved by the FDA or comparable foreign regulatory authorities for sale. To satisfy these standards, we and/or our collaborators must allocate resources among our various development programs and must engage in expensive and lengthy testing of our drug candidates. These discovery and development efforts for a new pharmaceutical product, including follow-on compounds, are resource-intensive and may take 10 to 15 years or longer for each drug candidate. Despite our efforts, our drug candidates may not:

•

offer therapeutic or other improvement over existing competitive drugs;



•

be proven safe and effective in clinical trials;



•

meet applicable regulatory standards;



•

be capable of being produced in commercial quantities at acceptable costs; or



•

if approved for commercial sale, be successfully marketed as pharmaceutical products.

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        In addition to our ongoing registration programs for telaprevir and VX-770, we have ongoing and planned Phase 2a clinical trials for a number of our earlier-stage drug candidates, including a planned clinical trial of telaprevir in combination with VX-222 in patients infected with HCV, a planned clinical trial of VX-809 in combination with VX-770 in patients with the most common CF mutation, a clinical trial of VX-509 in patients with moderate-to-severe RA and a clinical trial of VX-765 in patients with epilepsy. While we are heavily dependent on the success of our registration programs, the strength of our company's pipeline of drug candidates and potential drug candidates will depend in large part upon the outcomes of these ongoing and planned Phase 2a clinical trials. Findings, including toxicology findings, in nonclinical studies conducted concurrently with clinical trials as well as results of our clinical trials could lead to abrupt changes in our development activities, including the possible cessation of development activities associated with a particular drug candidate or program, including telaprevir or VX-770. Furthermore, results from our clinical trials may not meet the level of statistical significance required by the FDA or other regulatory authorities for approval of a drug candidate.

        We and many other companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in late-stage clinical trials even after achieving promising results in earlier-stage clinical trials. Accordingly, the results from the completed preclinical studies and clinical trials, positive results in preclinical studies and early clinical trials may not be replicated in later clinical trials, and ongoing clinical trials for our drug candidates may not be predictive of the results we may obtain in later-stage trials or of the likelihood of approval of a drug candidate for commercial sale. In addition, from time to time we report interim data from our clinical trials, including with respect to our HCV program data regarding patients' HCV RNA levels during treatment, at the end-of-treatment or 12 weeks after completion of treatment. Interim data are subject to change, and there can be no assurances that interim data will be confirmed upon the analysis of final data. In addition, interim data with respect to patients' HCV RNA levels may not be predictive of the final SVR rates that will be achieved in the clinical trial.

If we are unable to obtain United States and/or foreign regulatory approval, we will be unable to commercialize our drug candidates.

        Our drug candidates are subject to extensive governmental regulations relating to their development, clinical evaluation, manufacturing and commercialization. Rigorous nonclinical testing and clinical trials and an extensive regulatory approval process are required in the United States and in most other countries prior to the commercial sale of drug candidates. Satisfaction of these and other regulatory requirements is costly, time-consuming, uncertain and subject to unanticipated delays. It is possible that none of the drug candidates we are developing independently, or in collaboration with others, will be approved for marketing.

        We have limited experience in conducting and managing the late-stage clinical trials and NDA process necessary to obtain regulatory approvals, including approval by the FDA. The time required to complete clinical trials and to satisfy the FDA and other countries' regulatory review processes is uncertain and typically takes many years. Our analysis of data obtained from nonclinical and clinical activities is subject to confirmation and interpretation by regulatory authorities, which could delay, limit or prevent regulatory approval. We may also encounter unanticipated delays or increased costs due to government regulation from future legislation or administrative action or changes in FDA policy during the period of drug development, clinical trials and FDA regulatory review.

        Any delay in obtaining or failure to obtain required approvals could materially adversely affect our ability to successfully commercialize any drug candidate. Furthermore, any regulatory approval to market a drug may be subject to limitations that we do not currently expect on the indicated uses for which we may market the drug. Any such limitations could limit the size of the market for the drug.

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        We are also subject to numerous foreign regulatory requirements governing the conduct of clinical trials, manufacturing and marketing authorization, pricing and third-party reimbursement. The foreign regulatory approval process includes all of the risks associated with the FDA approval process described above, as well as risks attributable to the satisfaction of foreign requirements. Approval by the FDA does not ensure approval by regulatory authorities outside the United States. Foreign jurisdictions may have different approval procedures than those required by the FDA and may impose additional testing requirements for our drug candidates.

If clinical trials for our drug candidates are prolonged or delayed, we will be unable to commercialize our drug candidates as currently planned, which would require us to incur additional costs, would delay our receipt of any product revenue and could harm our competitive position.

        We cannot predict whether or not we will encounter problems with any of our completed, ongoing or planned clinical trials that will cause us or regulatory authorities to delay or suspend clinical trials, or delay the analysis of data from our completed or ongoing clinical trials. Any of the following could delay the clinical development of our drug candidates:

•

ongoing discussions with the FDA or comparable foreign authorities regarding the scope or design of our clinical trials and the number of clinical trials we must conduct;



•

delays in enrolling volunteers or patients into clinical trials, including as a result of low numbers of patients that meet the eligibility criteria for the trial;



•

a lower than anticipated retention rate of volunteers or patients in clinical trials;



•

the need to repeat clinical trials as a result of inconclusive results, unforeseen complications in testing or clinical investigator error;



•

inadequate supply or deficient quality of drug candidate materials or other materials necessary for the conduct of our clinical trials;



•

unfavorable FDA or foreign regulatory authority inspection and review of a manufacturing facility for a drug candidate or its relevant manufacturing records or a clinical trial site or records of any clinical or preclinical investigation;



•

unfavorable results from clinical trials of our drug candidates;



•

serious and unexpected drug-related side-effects experienced by participants in our clinical trials;



•

favorable results in testing of our competitors' drug candidates, or FDA or foreign regulatory authority approval of our competitors' products; or



•

action by the FDA or a foreign regulatory authority to place a clinical hold on a trial.

        Our ability to enroll patients in our clinical trials in sufficient numbers and on a timely basis will be subject to a number of factors, including the size of the patient population, the nature of the protocol, the proximity of patients to clinical sites, the availability of effective treatments for the relevant disease, the number of other clinical trials ongoing and competing for patients in the same indication and the eligibility criteria for the clinical trial. In addition, subjects may drop out of our clinical trials or may be lost to follow-up medical evaluation after treatment ends, and this could possibly impair the validity or statistical significance of the trials. Delays in patient enrollment or unforeseen drop-out rates may result in increased costs and longer development times. We are currently investing large amounts of money in research and development, the building of our commercial organization and the building of commercial supplies of telaprevir. Our revenues constitute only a small fraction of our total investment, which is being funded from various sources, including the sale of shares and convertible debt and payments from collaborators. Any significant delay in our planned timetable for launch of telaprevir, or disappointing sales post-launch would require us to either

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seek additional financing, which might not be available, or attempt to reduce costs through terminating existing programs, or the sale of assets, either of which might be difficult or insufficient.

        We, our collaborators, the FDA or other applicable regulatory authorities may suspend clinical trials of a drug candidate at any time if we or they believe the subjects or patients participating in such clinical trials are being exposed to unacceptable health risks or for other reasons. Any such suspension could materially adversely affect the development of a particular drug candidate and our business.

        In addition, it is impossible to predict whether legislative changes will be enacted, or whether FDA or other applicable regulatory authority regulations, guidance or interpretations will be changed, or what the impact of such changes, if any, may be. If we experience any such problems, we may not have the financial resources to continue development of the drug candidate that is affected or the development of any of our other drug candidates. Any delay in the approval of any of our drug candidates, including telaprevir, could also have a material adverse impact on our ability to effectively commercialize the drug candidate after approval if one or more of our competitors are able to bring competing therapies to market before or in closer proximity to the launch date for our drug candidates.

The results from our and our collaborators' clinical development activities and the clinical development activities of our competitors are released periodically, and have often resulted in significant volatility in the price of our common stock.

        Any new information regarding our drug candidates or potentially competitive drugs or drug candidates, and in particular any new information regarding telaprevir and potentially competitive HCV drug candidates, can substantially affect investors' perceptions regarding our future prospects. We, our collaborators and our competitors periodically provide updates regarding drug development programs, typically through press releases, conference calls and presentations at medical conferences. These periodic updates often include interim or final results from clinical trials conducted by us, our collaborators or our competitors and/or information about our or our competitors' expectations regarding future clinical development of our drug candidates or potentially competitive drugs or drug candidates. The timing of the release of information by us regarding our drug development programs is often beyond our control and is influenced by when we receive data from our clinical trials and by the general preference among pharmaceutical companies to disclose clinical data during medical conferences. In addition, because clinical trials of drug candidates for the treatment of HCV infection often occur over more than one year, the information that we, our collaborators and our competitors disclose may be based on interim rather than final data that may involve interpretation difficulties and may in any event not accurately reflect final results.

If our competitors bring superior drugs to market or bring their drugs to market before we do, we may be unable to find a market for our drug candidates.

        Our drug candidates in development may not be able to compete effectively with drugs that are currently on the market or new drugs that may be developed by others. There are many other companies developing drugs for the same indications that we are pursuing in development, in particular for the treatment of HCV infection. In order to compete successfully in these areas, we must demonstrate improved safety, efficacy and ease of manufacturing and gain market acceptance over competing drugs, such as Merck's boceprevir, that may receive regulatory approval before or after our drug candidates, and over those that currently are marketed. Many of our competitors, including major pharmaceutical companies such as Merck, Bristol-Myers Squibb, GlaxoSmithKline, Pfizer, Roche, Amgen, Novartis and Johnson & Johnson, possess substantially greater financial, technical and human resources than we possess. In addition, many of our competitors have significantly greater experience than we have in conducting nonclinical testing and human clinical trials of drug candidates, scaling up manufacturing operations and obtaining regulatory approvals of drugs and manufacturing facilities. Accordingly, our competitors may succeed in obtaining regulatory approval for drugs more rapidly than

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we do. No assurances can be given that telaprevir will be approved for marketing prior to boceprevir. If we obtain regulatory approval and launch commercial sales of our drug candidates, we also will compete with respect to manufacturing efficiency and sales and marketing capabilities, areas in which we currently have limited experience.

        We are aware of a number of companies that are developing new treatments for HCV infections including protease inhibitor compounds like telaprevir and boceprevir, polymerase inhibitor compounds, NS5A inhibitor compounds and advanced interferons. Even if we are able to obtain marketing approval for telaprevir, it is possible that one or more of these competing therapies could be approved prior to or shortly after we obtain such approval for telaprevir, or may be approved later but with an equal or better safety and efficacy profile, which we believe may negatively impact telaprevir sales.

If we are unable to develop effective independent sales and marketing capabilities or establish third-party relationships for the commercialization of our drug candidates, we will not be able to successfully commercialize our drug candidates, particularly telaprevir, even if we are able to obtain regulatory approval.

        We currently have limited experience as a company in sales and marketing or with respect to pricing and obtaining adequate third-party reimbursement for drugs. We are developing marketing capabilities and will need to develop an independent sales force in order to market telaprevir in North America and have entered into collaborations in order to market telaprevir in the rest of the world if it is approved. We will need to expand these capabilities and/or enter into additional arrangements with third parties to sell and market our other drug candidates, if they are approved for sale by regulatory authorities.

        In order to market telaprevir in North America if it is approved, we are building a marketing organization and will need to build a specialized sales force, which requires substantial efforts and significant management and financial resources. In addition, if VX-770 is approved, we would also need to establish a sales force in North America and Europe for VX-770. While we intend to stage our commitments to the extent possible in consideration of the development timelines, in order to support an effective launch of telaprevir, we will need to make significant financial commitments to our marketing organization prior to receiving regulatory approval. We will need to devote significant effort, in particular, to recruiting individuals with experience in the sales and marketing of pharmaceutical products. Competition for personnel with these skills is very high and may be particularly difficult for us since telaprevir is still an investigational drug candidate and we will be competing with companies that are currently marketing successful drugs. As a result, difficulties in successfully developing our own marketing capabilities or independent sales force for telaprevir in North America may adversely affect an effective launch of telaprevir if it is approved for sale.

        We have granted commercialization rights to other pharmaceutical companies with respect to certain of our drug candidates, including telaprevir, in specific geographic locations. To the extent that our collaborators have commercial rights to our drugs, any revenues we receive from sales of any approved drugs in those locations will depend primarily on the sales and marketing efforts of others, which we do not control and may not be able to effectively influence.

We are investing significant resources in our development program for VX-770, based primarily on data from a relatively small clinical trial in which patients received VX-770 over a short duration. If we are unable to show the safety and efficacy of VX-770, or experience delays in doing so, our business could be materially harmed.

        We are increasing the resources that we are investing in the development of VX-770 and began a registration program for VX-770 in the first half of 2009 focused on CF patients with the G551D mutation. We initiated this registration program based primarily on data from a Phase 2a clinical trial of VX-770 in 39 patients with CF, in which patients received VX-770 over 14-day and 28-day periods.

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This is a relatively small database from which to project the final outcomes of a drug development program. In order to receive approval for VX-770, we will need to show that VX-770 is safe and effective in a larger number of patients than were involved in the Phase 2a clinical trial, over significantly longer dosing periods. In addition, our registration program for VX-770 includes pediatric patient populations in which VX-770 has not previously been studied. Since a substantial portion of the CF population is under age 18, VX-770's potential commercial success will be dependent not only on marketing approval for adult patients, but also on approval for pediatric patients. If we are unable to show the safety and efficacy of VX-770 in the relevant patient populations, or experience delays in doing so, our business could be materially harmed.

If physicians, patients and third-party payors do not accept our future drugs, we may be unable to generate significant revenues, if any.

        Even if we obtain regulatory approval for our drug candidates, our approved drugs may not gain market acceptance among physicians and patients. We believe that effectively marketing telaprevir, if it is approved, and our other drug candidates, if any of them are approved, will require substantial efforts, both prior to launch and after approval. Physicians may elect not to prescribe our drugs, and patients may elect not to request or take them, for a variety of reasons including:

•

lower demonstrated clinical safety and efficacy compared to other drugs;



•

prevalence and severity of adverse side-effects;



•

lack of cost-effectiveness;



•

lack of reimbursement availability from third-party payors;



•

a decision to wait for the approval of other therapies that have significant perceived advantages over our drug candidates;



•

convenience and ease of administration;



•

other potential advantages of alternative treatment methods; and



•

ineffective marketing and distribution support.

        If our approved drugs fail to achieve market acceptance, we will not be able to generate significant revenues.

Government and other third-party payors seek to contain costs of health care through legislative and other means and if they fail to provide coverage and adequate payment rates for our future drugs, our revenues and prospects for profitability will be harmed.

        In both domestic and foreign markets, our sales of any future drugs will depend in part upon the availability of reimbursement from third-party payors. Third-party payors include government health programs such as Medicare and Medicaid, managed care providers, private health insurers and other organizations. Governments and other third-party payors generally seek to contain or reduce the costs of health care through various means. For example, in certain foreign markets, pricing or profitability of therapeutic and other pharmaceutical products is subject to governmental control. In the United States, there have been, and we expect that there will continue to be, a number of federal and state proposals to implement similar governmental control. Additional and broad health care proposals currently are being considered by the United States Congress. While we cannot predict whether any legislative or regulatory proposals will be adopted, the adoption of such proposals could have a material adverse effect on our business, financial condition and potential profitability.

        In addition, these third-party payors are increasingly attempting to contain health care costs by demanding price discounts or rebates and limiting both the types and variety of drugs that they will

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cover and the amounts that they will pay for these drugs. As a result, they may not cover or provide adequate payment for our future drugs. We might need to conduct post-marketing studies in order to demonstrate the cost-effectiveness of any future drugs to such payors' satisfaction. Such studies might require us to commit a significant amount of management time and financial and other resources. Our future drugs might not ultimately be considered cost-effective. Adequate third-party reimbursement might not be available to enable us to maintain price levels sufficient to realize an appropriate return on our investment in product development.

        Reimbursement rates may vary according to the use of the drug and the clinical setting in which it is used, may be based on payments allowed for lower-cost products that are already reimbursed, may be incorporated into existing payments for other products or services, and may reflect budgetary constraints and/or imperfections in Medicare or Medicaid data used to calculate these rates. Net prices for drugs may be reduced by mandatory discounts or rebates required by government health care programs. Such legislation, or similar regulatory changes or relaxation of laws that restrict imports of drugs from other countries, could reduce the net price we receive for our marketed drugs.

If our processes and systems are not compliant with regulatory requirements, we could be subject to delays in submitting NDAs or restrictions on marketing of drugs after they have been approved.

        We currently are developing drug candidates for regulatory approval for the first time since our inception, and are in the process of implementing regulated processes and systems required to obtain and maintain regulatory approval for our drug candidates. Certain of these processes and systems for conducting clinical trials and manufacturing material must be compliant with regulatory requirements before we can apply for regulatory approval for our drug candidates. These processes and systems will be subject to continual review and periodic inspection by the FDA and other regulatory bodies. If we are unable to achieve compliance in a timely fashion, or if compliance issues are identified at any point in the development and approval process, we may experience delays in filing for regulatory approval for our drug candidates, or delays in obtaining regulatory approval after filing. In addition, any later discovery of previously unknown problems or safety issues with approved drugs or manufacturing processes, or failure to comply with regulatory requirements, may result in restrictions on such drugs or manufacturing processes, withdrawal of drugs from the market, the imposition of civil or criminal penalties or a refusal by the FDA and/or other regulatory bodies to approve pending applications for marketing approval of new drugs or supplements to approved applications, any of which could have a material adverse effect on our business. In addition, we are a party to agreements that transfer responsibility for complying with specified regulatory requirements, such as filing and maintenance of marketing authorizations and safety reporting or compliance with manufacturing requirements, to our collaborators and third-party manufacturers. If our collaborators or third-party manufacturers do not fulfill these regulatory obligations, any drugs for which we or they obtain approval may be subject to later restrictions on manufacturing or sale, or may even risk withdrawal, which could have a material adverse effect on our business.

We depend on our collaborators to work with us to develop, manufacture and commercialize many of our drug candidates.

        We have granted development and commercialization rights for telaprevir to Janssen (worldwide other than North America and Far East) and to Mitsubishi Tanabe (Far East). We expect to receive significant financial support under our Janssen collaboration agreement, as well as meaningful technical and manufacturing contributions to the telaprevir program. The success of some of our key programs, such as for telaprevir, is dependent upon the continued financial and other support that our collaborators have agreed to provide. Each of our collaborators has significant discretion in determining the efforts and resources that it will apply to the collaboration.

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        The risks that we face in connection with these existing and any future collaborations include the following:

•

Our collaboration agreements are subject to termination under various circumstances, including, as in the case of our agreement with Janssen, termination without cause. Any such termination by Janssen could have a material adverse effect on our financial condition and/or delay the development and commercial sale of telaprevir.



•

Our collaborators may change the focus of their development and commercialization efforts or may have insufficient resources to effectively develop our drug candidates. Pharmaceutical and biotechnology companies historically have re-evaluated their development and commercialization priorities following mergers and consolidations, which have been common in recent years in these industries. The ability of some of our drug candidates to reach their potential could be limited if our collaborators decrease or fail to increase development or commercialization efforts related to those drug candidates.



•

Our collaboration agreements may have the effect of limiting the areas of research and development that we may pursue, either alone or in collaboration with third parties.



•

Our collaborators may develop and commercialize, either alone or with others, drugs that are similar to or competitive with the drugs or drug candidates that are the subject of their collaborations with us.

Our investment in the clinical development and manufacture of a commercial supply of telaprevir may not result in any benefit to us if telaprevir is not approved for commercial sale.

        We are investing significant resources in the clinical development of telaprevir. Telaprevir is the first drug candidate for which we expect to perform all activities related to late-stage development, drug supply, registration and commercialization in a major market. We are planning for and investing significant resources now in preparation for submitting an application for marketing approval, continuing to build our commercial supply inventories of drug product, and completing our scale-up of sales and marketing capacity. Our costs to obtain a commercial supply of telaprevir have included approximately $20 million, $17 million and $75 million in 2009, 2008 and 2007, respectively, and we expect these costs to increase as we near the potential launch of telaprevir. Our engagement in these resource-intensive activities puts significant investment at risk if we do not obtain regulatory approval and successfully commercialize telaprevir in North America. There is no assurance that our development of telaprevir will lead successfully to regulatory approval, or that obtaining regulatory approval will lead to commercial success of telaprevir. If telaprevir is not approved for commercial sale or if its development is delayed for any reason, our full investment in telaprevir may be at risk, we may face significant costs to dispose of unusable inventory, and our business and financial condition could be materially adversely affected.

We depend on third-party manufacturers, including sole source suppliers, to manufacture materials for clinical trials and expect to continue to rely on them to meet our commercial supply needs for any drug candidate that is approved for sale. We may not be able to maintain these relationships and could experience supply disruptions outside of our control.

        We currently rely on a worldwide network of third-party manufacturers to manufacture and distribute our drug candidates for clinical trials, and we expect that we will continue to rely on third parties for the foreseeable future to meet our commercial supply needs for any of our drug candidates that are approved for sale. As a result of our reliance on these third-party manufacturers and suppliers, including sole source suppliers of certain components of our drug candidates, we may be subject to significant supply disruptions outside of our control. Our supply chain for sourcing raw materials and manufacturing drug product ready for distribution is a multi-step international endeavor. Third-party

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contract manufacturers, including some in Asia, supply us with raw materials, and contract manufacturers in the European Union and the United States convert these raw materials into drug substance and convert the drug substance into final dosage form. Establishing and managing this global supply chain requires a significant financial commitment and the creation and maintenance of numerous third-party contractual relationships. Although we attempt to effectively manage the business relationships with companies in our supply chain, we do not have control over their operations. There can be no assurance that we will be able to establish and maintain commercial supply chains on commercially reasonable terms, or at all, in order to support a timely launch of telaprevir or any of our other drug candidates.

        We require a supply of telaprevir for our clinical trials, and have agreed to exercise our contractual rights from our third-party manufacturers to provide a supply of telaprevir to Janssen and Mitsubishi Tanabe for their clinical trials. We will require a supply of telaprevir for sale in North America if we are successful in obtaining marketing approval. We have completed the transfer of technical information regarding the manufacture of telaprevir to Janssen so that Janssen will be able to manufacture telaprevir, if approved, for sale in Janssen's territories and as a secondary supply source of drug substance for us. We believe there are multiple third parties capable of providing most of the materials and services we need in order to manufacture and distribute telaprevir. We also believe that supply of materials which cannot be second-sourced can be managed with inventory planning. However, there is a risk that we may underestimate or overestimate demand, and the manufacturing capacity for which we planned and contracted with third-party manufacturers may not be sufficient or may result in more inventory than is necessary. In addition, because of the significant lead times involved in our supply chain for telaprevir, we may have less flexibility to adjust our supply in response to changes in demand than if we had shorter lead times.

        We require a supply of VX-770 for clinical trials in North America and Europe, and will require a supply of VX-770 for sale in North America and Europe if we obtain marketing approval. We obtain VX-770 to meet our clinical supply needs through a third-party manufacturer network and are focused on completing the technical development work to produce VX-770 at a commercial scale. We are in the process of expanding our existing relationships with our third-party manufacturers and establishing new relationships with third-party manufacturers, in order to establish the supply chain for VX-770 that would be required to support the potential commercial launch of VX-770.

        Even if we successfully establish arrangements with third-party manufacturers, supply disruptions may result from a number of factors, including shortages in product raw materials, labor or technical difficulties, regulatory inspections or restrictions, shipping or customs delays or any other performance failure by any third-party manufacturer on which we rely.

        Any supply disruptions could impact the timing of our clinical trials and the commercial launch of any approved drugs. Furthermore, we may be required to modify our production methods to permit us to economically manufacture our drugs for commercial launch and sale. These modifications may require us to re-evaluate our resources and the resources of our third-party manufacturers, which could result in abrupt changes in our production methods and supplies. Upon approval of a drug for sale, if any, we similarly may be at risk of supply chain disruption for our commercial drug supply.

        In the course of its services, a contract manufacturer may develop process technology related to the manufacture of our drug candidates that the manufacturer owns, either independently or jointly with us. This would increase our reliance on that manufacturer or require us to obtain a license from that manufacturer in order to have our products manufactured by other suppliers utilizing the same process.

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We may need to raise additional capital that may not be available.

        We expect to incur substantial expenses as we design and develop existing and future compounds, undertake clinical trials, and build our drug supply, regulatory, development and commercial capabilities. We also expect to incur substantial administrative and commercialization expenses. As a result, we may raise additional capital in order to maintain adequate working capital and cash reserves to continue our diversified research, discovery and development efforts and expect we would need additional capital if the development of telaprevir were materially delayed. We anticipate that we would finance any additional cash needs with some combination of:

•

public offerings or private placements of our debt or equity securities or other methods of financing;



•

cash received from existing and future collaborative agreements; and



•

future product sales.

        While we believe that our current cash, cash equivalents and marketable securities, will be sufficient to fund our operations for the next twelve months, we may raise additional capital through public offerings or private placements of our debt or equity securities. Any such capital transactions may or may not be similar to the transactions that we have completed in the past. Any debt financing may be on terms that, among other things, include conversion features that could result in dilution to our then-existing security holders and restrict our ability to pay interest and dividends—although we do not intend to pay dividends for the foreseeable future. Any equity financings would result in dilution to our then-existing security holders. If adequate funds are not available on acceptable terms, or at all, we may be required to curtail significantly or discontinue one or more of our research, drug discovery or development programs, including clinical trials, incur significant cash exit costs, or attempt to obtain funds through arrangements with collaborators or others that may require us to relinquish rights to certain of our technologies, drugs or drug candidates. Based on many factors, including general economic conditions, additional financing may not be available on acceptable terms, if at all.

We may not be successful in developing any of the drug candidates we acquired in our March 2009 acquisition of ViroChem and, as a result, we may not realize any benefits from this acquisition and could be subject to significant impairment charges in future periods.

        In March 2009, we acquired ViroChem for $100.0 million in cash and 10.7 million shares of our common stock. We acquired ViroChem primarily in order to secure rights to two HCV polymerase inhibitors, VX-222 and VX-759, as part of our strategy to pursue drug candidates that could potentially be developed in combination with telaprevir and/or our earlier-stage drug candidates. VX-222 and VX-759 were still in Phase 1 clinical development at the time of the acquisition and have only been evaluated in nonclinical studies and in a limited number of patients infected with HCV. While we believe the data from the clinical trials to date, together with studies in animal models and in vitro data, support the development of combination therapies, there are numerous reasons why we may not be able to successfully develop a combination therapy involving either VX-222 or VX-759, including:

•

data from trials involving drug candidates evaluated separately may not predict possible outcomes, such as unforeseen drug interactions, from drug candidates dosed in combination, which could negatively impact the efficacy and safety profile of the combination product candidate;



•

positive results in small clinical trials and nonclinical studies may not be predictive of results in clinical trials involving large numbers of patients; and



•

favorable results of testing or earlier FDA or foreign regulatory approval of competitors' products.

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There can be no assurance that we will be able to successfully develop either VX-222 or VX-759 alone or in combination with telaprevir or our other HCV protease inhibitors, and if we are not successful in developing VX-222 or VX-759, we may not realize any benefits from our March 2009 acquisition of ViroChem.

        At the time of acquisition, we allocated $525.9 million to intangible assets related to the in-process research and development associated with the ViroChem drug candidates. In the fourth quarter of 2009, we recorded expense of $7.2 million in connection with an impairment of the intangible assets related to VCH-286, a drug candidate for the treatment of HIV infection that we acquired from ViroChem. At December 31, 2009, our consolidated balance sheet included $518.7 million of intangible assets related to in-process research and development, approximately 80% of which related to VX-222 and approximately 20% of which related to VX-759. If the value of these drug candidates, and in particular VX-222, becomes impaired, we may incur significant impairment charges, including potentially the entire amount of the intangible assets reflected on our consolidated balance sheet associated with the drug candidate, in the period in which the impairment becomes known. An impairment could result from, among other things, unfavorable safety or efficacy results from clinical trials or nonclinical studies or competitive factors affecting the potential market for the drug candidate. VX-759, which is considered a backup compound to VX-222, could be impaired by data pertaining to the potential successful development of VX-222, which could result in a significant impairment charge in the period in which that determination is made. If we incur a significant impairment charge in a future period related to the intangible assets acquired in the ViroChem transaction, the value of our common stock could decrease.

We rely on third parties to conduct our clinical trials, and those third parties may not perform satisfactorily, including failing to meet established deadlines for the completion of such trials.

        We do not have the ability to independently conduct clinical trials for our drug candidates, and we rely on third parties such as contract research organizations to help manage our clinical trial process and on medical institutions and clinical investigators to enroll qualified patients and conduct our clinical trials. Our reliance on these third parties for clinical development activities reduces our control over these activities. Accordingly, these third-party contractors may not complete activities on schedule, or may not conduct our clinical trials in accordance with regulatory requirements or our trial design. If these third parties do not successfully carry out their contractual duties or meet expected deadlines, we may be required to replace them. Although we believe that there are a number of other third-party contractors we could engage to continue these activities, it may result in a delay of the affected trial. If clinical trials are not conducted in accordance with our contractual expectations or regulatory requirements, action by regulatory authorities might significantly and adversely affect the conduct or progress of these trials or in specific circumstances might result in a requirement that a trial be redone. Accordingly, our efforts to obtain regulatory approvals for and commercialize our drug candidates could be delayed.

Issuances of additional shares of our common stock could cause the price of our common stock to decline.

        As of December 31, 2009, we had 200.0 million shares of common stock issued and outstanding. As of December 31, 2009, we also had outstanding options to purchase 19.2 million shares of common stock with a weighted-average exercise price of $31.38 per share. Outstanding vested options are likely to be exercised if the market price of our common stock exceeds the applicable exercise price. In addition, we may issue additional common stock or restricted securities in the future as part of our financing activities or business development activities and any such issuances may have a dilutive effect on existing shareholders. Sales of substantial amounts of our common stock in the open market, or the availability of such shares for sale, could adversely affect the price of our common stock. In addition, the issuance of restricted common stock or common stock upon exercise of any outstanding options would be dilutive, and may cause the market price for a share of our common stock to decline.

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Outstanding indebtedness may make it more difficult to obtain additional financing or reduce our flexibility to act in our best interests.

        As of December 31, 2009, we had outstanding $32.1 million in aggregate principal amount of our 4.75% Convertible Senior Subordinated Notes due 2013, or 2013 Notes. In February 2010, we announced that we will redeem the 2013 Notes on March 19, 2010 and will be obligated to redeem the 2013 Notes at the redemption price if the 2013 Notes are not earlier converted by the holders, as expected, into shares of our common stock. We also are obligated to repay an aggregate of $155.0 million no later than October 31, 2012 as a result of our issuance of our secured notes due 2012, or the 2012 Notes. We have issued significant amounts of convertible debt in the past and may issue additional convertible debt or incur other types of indebtedness in the future. The level of our indebtedness could affect us by:

•

making it more difficult to obtain additional financing for working capital, capital expenditures, debt service requirements or other purposes;



•

constraining our ability to react quickly in an unfavorable economic climate or to changes in our business or the pharmaceutical industry; or



•

requiring the dedication of substantial cash to service the repayment of any outstanding debt, including periodic interest payments, thereby reducing the amount of cash available for other purposes.

If we acquire or license technologies, resources or drug candidates, we will incur a variety of costs and may never realize benefits from the transaction.

        If appropriate opportunities become available, we might attempt to license or acquire technologies, resources and drugs or drug candidates, including potentially complimentary HCV therapies. The process of negotiating the license or acquisition might result in operating difficulties and expenditures and, whether or not any such transaction is ever consummated, might require significant management attention that would otherwise be available for ongoing development of our business. Moreover, even if we complete a license or other transaction, we might never realize the anticipated benefits of the transaction or we may incur impairment charges related to assets acquired in any such transaction. For example, in the fourth quarter of 2009, we recorded expense of $7.2 million in connection with an impairment of the intangible assets related to VCH-286, a drug candidate for the treatment of HIV infection that we acquired from ViroChem. Future licenses or acquisitions could result in potentially dilutive issuances of equity securities, the incurrence of debt, the creation of contingent liabilities, impairment expenses related to goodwill, and impairment or amortization expenses related to other intangible assets, which could harm our financial condition.

If we obtain regulatory approvals, our drug candidates will be subject to ongoing regulatory review. If we fail to comply with continuing United States and applicable foreign regulations, we could lose those approvals, and our business would be seriously harmed.

        If we receive regulatory approval of any drug candidates that we are developing, we will be subject to continuing regulatory review, including the review of clinical results that are reported after our drug candidates become commercially available. Drugs are more widely used by patients once approval has been obtained, and therefore side-effects and other problems may be observed after approval that were not seen or anticipated during pre-approval clinical trials. In addition, the manufacturers and the manufacturing facilities we engage to make any of our drug candidates will also be subject to periodic review and inspection by the FDA. The subsequent discovery of previously unknown problems with the drug, manufacturers or manufacturing facilities may result in restrictions on the drug, manufacturers or manufacturing facilities, including withdrawal of the drug from the market, our inability to use the facilities to make our drug or a determination that drug inventories are not safe for commercial sale. If

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we fail to comply with applicable continuing regulatory requirements, we may be subject to fines, suspension or withdrawal of regulatory approval, product recalls and seizures, operating restrictions and/or criminal prosecutions.

Our drug development efforts are data-driven and therefore potentially subject to abrupt changes in expected outcomes.

        Small molecule drug discovery and development involve, initially, the identification of chemical compounds that may have promise as treatments for specific diseases. Once identified as drug candidates, compounds are subjected to years of testing in a laboratory setting, in animals and in humans. Our ultimate objective is to determine whether the drug candidates have physical characteristics, both intrinsically and in animal and human systems, and a toxicological profile, that are compatible with clinical and commercial success in the treatment of the disease being targeted. Throughout this process, experiments are conducted and data are gathered that could reinforce a decision to move to the next step in the investigation process for a particular drug candidate, could result in uncertainty over the proper course to pursue or could result in the termination of further drug development efforts with respect to the compound being evaluated. We monitor the results of our discovery research and our nonclinical studies and clinical trials and regularly evaluate and re-evaluate our portfolio investments with the objective of balancing risk and potential return in view of new data and scientific, business and commercial insights. This process can result in relatively abrupt changes in focus and priority as new information comes to light and we gain additional insights into ongoing programs and potential new programs.

We may not have the resources to develop and commercialize all the drug candidates for which we have rights and we may not be able to attract collaborators for the development and commercialization of these drug candidates

        As part of our ongoing strategy, we expect to seek additional collaborative arrangements. We have a number of research programs and early-stage and mid-stage clinical development programs. Depending on how these programs progress, we may not have the funding and/or the personnel to continue the development and commercialization of all of these programs internally. At any time, we may make the determination that in order to continue development of a drug candidate or program we need to identify a collaborator. Potentially, and depending on the circumstances, we may desire that a collaborator either agree to fund portions of a drug development program led by us, or agree to provide all the funding and directly lead the development and commercialization of a program. No assurance can be given that any efforts we make to seek additional collaborative arrangements will be successfully completed on a timely basis or at all. If we are unable to enter into acceptable collaborative relationships, one or more of our development programs could be delayed or terminated, and the possibility of our receiving a return on our investment in the program could be impaired.

Risks associated with our international business relationships could materially adversely affect our business.

        We have manufacturing, collaborative and clinical trial relationships, and we and our collaborators are seeking approval for our drug candidates, outside the United States. In addition, we expect that if telaprevir is approved for commercial sale, a significant portion of our commercial supply chain, including sourcing of raw materials and manufacturing, will be located in Asia and the European Union. Consequently, we are, and will continue to be, subject to risks related to operating in foreign countries. Risks associated with conducting operations in foreign countries include:

•

differing regulatory requirements for drug approvals in foreign countries;



•

unexpected changes in tariffs, trade barriers and regulatory requirements;

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•

economic weakness, including inflation, or political instability in particular foreign economies and markets;



•

compliance with tax, employment, immigration and labor laws for employees living or traveling abroad;



•

foreign taxes, including withholding of payroll taxes;



•

foreign currency fluctuations, which could result in increased operating expenses or reduced revenues, and other obligations incident to doing business or operating a subsidiary in another country;



•

workforce uncertainty in countries where labor unrest is more common than in the United States;



•

production shortages resulting from any events affecting raw material supply or manufacturing capabilities abroad; and



•

business interruptions resulting from geo-political actions, including war and terrorism.

        These and other risks associated with our international operations could materially adversely affect our business.

If we fail to expand our human resources, and in particular our commercial organization, and manage our growth effectively, our business may suffer.

        We expect that if our clinical drug candidates continue to progress in development and our drug discovery efforts continue to generate drug candidates, we will require significant additional investment in personnel, management systems and resources, particularly in the build out of our commercial capabilities. In advance of the potential approval of telaprevir we will need to build the commercial organization that will be responsible for the commercial launch of telaprevir, if it receives marketing approval, in the United States. The number of our full-time employees increased by 6% in 2009 and 18% in 2008, and we expect to experience additional growth in 2010. Because our drug discovery and development activities are highly technical in nature, we require the services of highly qualified and trained scientists who have the skills necessary to conduct these activities. In addition, as we attempt to grow our capabilities with respect to clinical development, regulatory affairs, quality control and sales and marketing, we need to attract and retain employees with experience in these fields. We face intense competition for our personnel from our competitors, our collaborators and other companies throughout our industry. Moreover, the growth of local biotechnology companies and the expansion of major pharmaceutical companies into the Boston area have increased competition for the available pool of skilled employees, especially in technical fields, and the high cost of living in the Boston and San Diego areas makes it difficult to attract employees from other parts of the country to these areas. Our ability to commercialize our drug candidates, achieve our research and development objectives, and satisfy our commitments under our collaboration agreements depends on our ability to respond effectively to these demands and expand our internal organization to accommodate additional anticipated growth. If we are unable to hire qualified personnel or manage our growth effectively, there could be a material adverse effect on our business.

The loss of the services of key employees or the failure to effectively integrate key employees could negatively impact our business and future growth.

        Our future success will depend in large part on our ability to retain the services of our key scientific and management personnel and to integrate new scientific and management personnel into our business. As we expand our capabilities in anticipation of the possible launch of commercial products, a loss of key personnel or a failure to properly integrate new personnel could be disruptive.

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We have entered into employment agreements with some individuals and provide compensation-related benefits to all of our key employees that vest over time and therefore induce them to remain with us. However, the employment agreements can be terminated by the employee on relatively short notice. The value to employees of stock-related benefits that vest over time—such as options and restricted stock—will be significantly affected by movements in our stock price that we cannot control, and may at any point in time be insufficient to counteract more lucrative offers from other companies. A failure to retain, as well as hire, train and effectively integrate into our organization a sufficient number of qualified scientists, professionals, sales personnel and senior management would negatively affect our business and our ability to grow our business.

If our patents do not protect our drugs, or our drugs infringe third-party patents, we could be subject to litigation and substantial liabilities.

        We have numerous issued patents and patent applications pending in the United States, as well as foreign counterparts in other countries. Our success will depend, in significant part, on our ability to obtain and maintain United States and foreign patent protection for our drugs, their uses and our processes, to preserve our trade secrets and to operate without infringing the proprietary rights of third parties. In particular, we believe that composition-of-matter claims are generally the most significant patent claims for companies in our segment of the pharmaceutical industry that focus on small molecule drug candidates that are new chemical compounds. While we currently have patents or patent applications with composition-of-matter claims for each of our more advanced clinical drug candidates, only a portion of these patents have been granted at this time. We cannot be certain that any patents will issue from our patent applications or, even if patents issue or have issued, that the issued claims will provide us with any significant protection against competitive products or otherwise be valuable commercially.

        Legal standards relating to the validity of patents and the proper scope of their claims in the pharmaceutical field are still evolving, and there is no consistent law or policy regarding the valid breadth of claims in biopharmaceutical patents or the effect of prior art on them. If we are not able to obtain adequate patent protection, our ability to prevent competitors from making, using and selling similar drugs will be limited. Furthermore, our activities may infringe the claims of patents held by third parties. Defense and prosecution of infringement or other intellectual property claims, as well as participation in other inter-party proceedings, can be expensive and time-consuming, regardless of whether or not the outcome is favorable to us. If the outcome of any such litigation or proceeding were adverse, we could be subject to significant liabilities to third parties, could be required to obtain licenses from third parties or could be required to cease sales of affected drugs, any of which outcomes could have a material adverse effect on our business.

Our business has a substantial risk of product liability claims. If we are unable to obtain appropriate levels of insurance, a product liability claim could adversely affect our business.

        Our business exposes us to significant potential product liability risks that are inherent in the development, clinical testing, manufacturing and sales and marketing of human therapeutic products. We currently have clinical trial insurance and will seek to obtain product liability insurance prior to the sales and marketing of any of our drug candidates. However, our insurance may not provide adequate coverage against potential liabilities. Furthermore, clinical trial and product liability insurance is becoming increasingly expensive. As a result, we may be unable to maintain current amounts of insurance coverage or obtain additional or sufficient insurance at a reasonable cost to protect against losses that could have a material adverse effect on us. If a claim is brought against us, we might be required to pay legal and other expenses to defend the claim, as well as uncovered damages awards resulting from a claim brought successfully against us. Furthermore, whether or not we are ultimately

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successful in defending any such claims, we might be required to direct significant financial and managerial resources to such defense, and adverse publicity is likely to result.

If we do not comply with laws regulating the protection of the environment and health and human safety, our business could be adversely affected.

        Our research and development efforts involve the controlled use of hazardous materials, chemicals and various radioactive compounds. Although we believe that our safety procedures for handling and disposing of these materials comply with the standards prescribed by state and federal regulations, the risk of accidental contamination or injury from these materials cannot be eliminated. If an accident occurs, we could be held liable for resulting damages, which could be substantial. We are also subject to numerous environmental, health and workplace safety laws and regulations, including those governing laboratory procedures, exposure to blood-borne pathogens and the handling of biohazardous materials. Although we maintain workers' compensation insurance to cover us for costs we may incur due to injuries to our employees resulting from the use of these materials, this insurance may not provide adequate coverage against potential liabilities. Due to the small amount of hazardous materials that we generate, we have determined that the cost to secure insurance coverage for environmental liability and toxic tort claims far exceeds the benefits. Accordingly, we do not maintain any insurance to cover pollution conditions or other extraordinary or unanticipated events relating to our use and disposal of hazardous materials. Additional federal, state and local laws and regulations affecting our operations may be adopted in the future. We may incur substantial costs to comply with, and substantial fines or penalties if we violate, any of these laws or regulations.

We have adopted anti-takeover provisions and are subject to Massachusetts corporate laws that may frustrate any attempt to remove or replace our current management or effectuate a business combination involving Vertex.

        Our corporate charter and by-law provisions, Massachusetts state laws and our stockholder rights plan may discourage certain types of transactions involving an actual or potential change of control of Vertex that might be beneficial to us or our security holders. Our charter provides for staggered terms for the members of the Board of Directors. Our by-laws grant the directors a right to adjourn annual meetings of stockholders, and certain provisions of our by-laws may be amended only with an 80% stockholder vote. Pursuant to our stockholder rights plan, each share of common stock has an associated preferred share purchase right. The rights will not trade separately from the common stock until, and are exercisable only upon, the acquisition or the potential acquisition through tender offer by a person or group of 15% or more of the outstanding common stock. We may issue shares of any class or series of preferred stock in the future without stockholder approval and upon such terms as our Board of Directors may determine. The rights of the holders of common stock will be subject to, and may be adversely affected by, the rights of the holders of any class or series of preferred stock that may be issued in the future. Massachusetts state law prohibits us from engaging in specified business combinations, unless the combination is approved or consummated in a prescribed manner, and prohibits voting by any stockholder who acquires 20% or more of our voting stock without stockholder approval. As a result, stockholders or other parties may find it more difficult to remove or replace our current management.

Our stock price may fluctuate based on factors beyond our control.

        Market prices for securities of companies such as ours are highly volatile. From January 1, 2008 to December 31, 2009, our common stock traded between $13.84 and $44.04 per share. The market for our stock, like that of other companies in the biotechnology field, has from time to time experienced

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significant price and volume fluctuations that are unrelated to our operating performance. The future market price of our securities could be significantly and adversely affected by factors such as:

•

announcements of results of clinical trials or nonclinical studies relating to our drug candidates or those of our competitors;



•

announcements of financial results and other operating performance measures, or capital structuring or financing activities;



•

technological innovations or the introduction of new drugs by our competitors;



•

government regulatory action;



•

public concern as to the safety of drugs developed by others;



•

developments in patent or other intellectual property rights or announcements relating to these matters;



•

developments in domestic and international governmental policy or regulation, for example relating to intellectual property rights;



•

developments relating specifically to other companies and market conditions for pharmaceutical and biotechnology stocks or stocks in general; and



•

general worldwide or national economic, political and capital market conditions.

Our estimates of our liability under our Kendall Square lease may be inaccurate.

        We leased a 290,000 square foot facility in Kendall Square, Cambridge, Massachusetts in January 2003 for a 15-year term. We currently are not occupying the entire facility. We have sublease arrangements in place for the remaining rentable square footage of the facility. In determining our obligations under the lease for the part of the facility that we are not occupying, we have made certain assumptions relating to the time necessary to sublease the space after the expiration of the initial subleases, projected future sublease rental rates and the anticipated durations of future subleases. Our estimates have changed in the past, and may change in the future, resulting in additional adjustments to the estimate of liability, and the effect of any such adjustments could be material.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

        This Annual Report on Form 10-K and, in particular, the description of our Business set forth in Item 1, the Risk Factors set forth in this Item 1A and our Management's Discussion and Analysis of Financial Condition and Results of Operations set forth in Item 7 contain or incorporate a number of forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, including statements regarding:

•

our expectations regarding clinical trials, development timelines and regulatory authority filings and submissions for telaprevir, VX-770, VX-809, VX-509, VX-222, VX-765 and other drug candidates under development by us and our collaborators, including our intention to submit an NDA for telaprevir in the United States in the second half of 2010, the potential of submitting an NDA for VX-770 in the second half of 2011 and the potential commercial launch of telaprevir in the United States in 2011;



•

our expectations regarding the expected date by which SVR data will be available and/or publicly announced for our ADVANCE, REALIZE and ILLUMINATE trials, and our expectations regarding the number of patients that will be evaluated, the trial design that will be utilized, the anticipated date by which enrollment will be completed and the expected date

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interim data and/or final data will be available and/or publicly announced for our ongoing clinical trials in the ENDEAVOR registration program for VX-770, including the STRIVE, ENVISION and DISCOVER trials, and for the planned and ongoing clinical trials of VX-809, VX-222, VX-509, VX-765 and other drug candidates under development by us;

•

expectations regarding the amount of, timing of and trends with respect to our revenues, our costs and expenses and other gains and losses, including those related to the intangible assets associated with the ViroChem acquisition and to the liabilities we recorded in connection with the financial transactions that we entered into in September 2009;



•

our belief that if we are able to successfully commercialize telaprevir in accordance with current development timelines, we will begin receiving cash flows from the sale of telaprevir in 2011;



•

the data that will be generated by ongoing and planned clinical trials, and the ability to use that data for the design and initiation of further clinical trials and to support regulatory filings, including potentially applications for marketing approval for telaprevir and VX-770;



•

our plan to begin clinical evaluation of novel combination regimens of telaprevir with VX-222 in the first quarter of 2010, and the possibility that we will begin evaluation of combination regimens of VX-770 and VX-809 in patients with CF in the second half of 2010;



•

our expectations regarding the future market demand and medical need for telaprevir and our other drug candidates;



•

our beliefs regarding the support provided by clinical trials and preclinical and nonclinical studies of our drug candidates for further investigation, clinical trials or potential use as a treatment of those drug candidates;



•

our ability to successfully market telaprevir and VX-770 or any of our other drug candidates if we are able to obtain regulatory approval;



•

the focus of our drug development efforts and our financial and management resources and our plan to invest significant resources in telaprevir and our other drug candidates;



•

the establishment, development and maintenance of collaborative relationships;



•

potential business development activities, including with respect to our JAK3 program;



•

our ability to use our research programs to identify and develop new drug candidates to address serious diseases and significant unmet medical needs;



•

our expectation that holders of our 2013 Notes will convert the 2013 Notes into shares of our common stock;



•

our estimates regarding obligations associated with a lease of a facility in Kendall Square, Cambridge, Massachusetts; and



•

our liquidity and our expectations regarding our needs for and ability to raise additional capital.

        Any or all of our forward-looking statements in this Annual Report on Form 10-K may turn out to be wrong. They can be affected by inaccurate assumptions we might make or by known or unknown risks and uncertainties. Many factors mentioned in this Annual Report on Form 10-K will be important in determining future results. Consequently, no forward-looking statement can be guaranteed. Actual future results may vary materially from expected results. We also provide a cautionary discussion of risks and uncertainties under "Risk Factors" above in this Item 1A. These are factors and uncertainties that we think could cause our actual results to differ materially from expected results. Other factors and uncertainties besides those listed there could also adversely affect us.

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        Without limiting the foregoing, the words "believes," "anticipates," "plans," "intends," "expects" and similar expressions are intended to identify forward-looking statements. There are a number of factors and uncertainties that could cause actual events or results to differ materially from those indicated by such forward-looking statements, many of which are beyond our control, including the factors and uncertainties set forth under "Risk Factors" above in this Item 1A. In addition, the forward-looking statements contained herein represent our estimate only as of the date of this filing and should not be relied upon as representing our estimate as of any subsequent date. While we may elect to update these forward-looking statements at some point in the future, we specifically disclaim any obligation to do so to reflect actual results, changes in assumptions or changes in other factors affecting such forward-looking statements.

ITEM 1B.    UNRESOLVED STAFF COMMENTS

        We did not receive any written comments from the Securities and Exchange Commission prior to the date 180 days before the end of the fiscal year ended December 31, 2009 regarding our filings under the Securities Exchange Act of 1934, as amended, that have not been resolved.

ITEM 2.    PROPERTIES

        We lease an aggregate of approximately 1,000,000 square feet of laboratory and office space in facilities located in Cambridge, Massachusetts, San Diego, California, Washington, DC, Coralville, Iowa, Montreal, Canada, and the United Kingdom. We believe our facilities are adequate for our current needs.

Cambridge, Massachusetts

        We lease an aggregate of 815,000 square feet of space in ten facilities situated in close proximity to our corporate headquarters located at 130 Waverly Street in Cambridge, Massachusetts. We lease approximately 100,000 square feet of laboratory and office space in our 130 Waverly Street corporate headquarters and approximately 192,000 square feet of laboratory and office space at 200 Sidney Street, located adjacent to our corporate headquarters. The 130 Waverly Street and 200 Sidney Street leases expire on December 31, 2015, with two options to extend for additional consecutive five-year terms. The lease for 21,000 square feet of office space at 21 Erie Street, also located adjacent to our corporate headquarters, expires in May 2012, with an option to extend for two additional consecutive five-year terms.

        The lease for our Kendall Square, Cambridge, Massachusetts facility will expire in 2018. We have the option to extend this lease for two consecutive ten-year terms. We have subleased approximately 145,000 square feet of the Kendall Square facility, and are using the remaining square feet of space leased in the facility for our research operations. The subleases are for terms ending in 2011 and 2012 with extension options to 2015 and 2018. One of the subleases has certain termination provisions beginning in 2010.

        We sublease approximately 145,000 square feet at 88 Sidney Street as subtenant to Alkermes, Inc. who is the prime tenant in the building. The sublease expires in June 2012 with an option to extend through 2014.

San Diego, California

        We lease approximately 81,000 square feet of laboratory and office space in San Diego, California. The lease for this space will expire on September 30, 2013. We have the option to extend this lease for one additional term of five years.

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United Kingdom

        We lease approximately 22,000 square feet of laboratory and office space in Milton Park, Abingdon, England, for our United Kingdom business and research and development activities, under a lease expiring in 2013. We also lease an additional 41,000 square feet of laboratory and office space in Milton Park under a lease with a term that expires in 2024. This lease has certain termination provisions in 2014 and 2019.

ITEM 3.    LEGAL PROCEEDINGS

        We are not a party to any material legal proceedings. We are not a party to any litigation in any court with any governmental authority, and management is not aware of any contemplated proceeding by any governmental authority against us.

ITEM 4.    SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

        There were no matters submitted to a vote of security holders during the quarter ended December 31, 2009.

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PART II

ITEM 5.    MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

Market Information

        Our common stock is traded on The Nasdaq Global Select Market under the symbol "VRTX." The following table sets forth for the periods indicated the high and low sale prices per share of our common stock as reported by Nasdaq:

Stockholders

        As of February 16, 2010, there were 1,655 holders of record of our common stock.

Performance Graph

CUMULATIVE TOTAL RETURN
Based on Initial Investment of $100 on December 31, 2004
with dividends reinvested (fiscal years ended December 31)

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Dividends

        We have never declared or paid any cash dividends on our common stock, and we currently expect that future earnings, if any, will be retained for use in our business.

Issuer Repurchases of Equity Securities

        The table set forth below shows all repurchases of securities by us during the three months ended December 31, 2009:

        The repurchases were made under the terms of our 1996 Stock and Option Plan and 2006 Stock and Option Plan. Under these plans, we may award shares of restricted stock to our employees and consultants that typically are subject to a lapsing right of repurchase by us. We may exercise this right of repurchase in the event that a restricted stock recipient's service to us is terminated. If we exercise this right, we are required to repay the purchase price paid by or on behalf of the recipient for the repurchased restricted shares, which typically is the par value per share of $0.01. Repurchased shares are returned to the applicable Stock and Option Plan under which they were issued. Shares returned to the 2006 Stock and Option Plan are available for future awards under the terms of that plan.

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ITEM 6.    SELECTED FINANCIAL DATA

        The following unaudited selected consolidated financial data are derived from our audited consolidated financial statements. These data should be read in conjunction with our audited consolidated financial statements and related notes that are included elsewhere in this Annual Report on Form 10-K and with "Management's Discussion and Analysis of Financial Condition and Results of Operations" included in Item 7 below.

(1)

The acquisition-related expenses, the intangible assets, the goodwill, the deferred tax liability and intangible asset impairment charge reflected in the selected financial data relate to our acquisition of ViroChem in 2009. See Note Q to our consolidated financial statements included elsewhere in this Annual Report on Form 10-K.

(2)

We recorded a $1.0 million benefit in 2006 due to the cumulative effect of estimating forfeitures on the grant date rather than recording them as they occur, which decreased the basic and diluted net loss per common share by $0.01.

(3)

The loss on derivative instruments, secured notes (due 2012), net and liability related to sale of potential future milestone payments reflected in the selected financial data relate to two financial transactions that we entered into in September 2009 relating to future milestone payments under our collaboration agreement with Janssen. See Note R to our consolidated financial statements included elsewhere in this Annual Report on Form 10-K.

(4)

Other gain/losses includes losses on exchanges of convertible notes of $18.1 million in 2009, $5.2 million in 2006 and $48.2 million in 2005 and a realized gain on sale of investment of $11.2 million in 2006.

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ITEM 7.    MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Overview

        We are in the business of discovering, developing and commercializing small molecule drugs for the treatment of serious diseases. Telaprevir, our lead drug candidate, is being evaluated in a fully-enrolled registration program focused on treatment-naïve and treatment-failure patients with genotype 1 HCV infection. We currently intend to submit an NDA for telaprevir in the United States in the second half of 2010, assuming the successful completion of the registration program. If we are able to obtain marketing approval for telaprevir in accordance with our current development and regulatory timelines, we expect to initiate sales of telaprevir in the United States in 2011. We are pursuing a number of other clinical development programs, including a registration program for VX-770, the lead drug candidate in our cystic fibrosis program. We plan to continue investing in our research and development programs and to develop selected drug candidates that emerge from those programs, alone or with third-party collaborators.

Business Focus

        Over the last several years, we have invested significant financial and management resources in the late-stage development of telaprevir and in strengthening our pipeline of drug candidates, through research and development activities and the acquisition of ViroChem Pharma Inc. To fund these investments, we have raised an aggregate of approximately $1.9 billion over the three years ended December 31, 2009, through sales of common stock and convertible debt, other financial transactions and one-time license fees. In order to execute our business plan and achieve profitability, we will need to complete the development of telaprevir on a timely basis and effectively commercialize telaprevir in the United States, where we have retained marketing rights to telaprevir.

        Over the next several years we believe that in addition to telaprevir we will need to further investigate other potential therapies for the treatment of HCV and to research, develop and commercialize additional drug candidates in other therapeutic areas with significant unmet need. As a result, we are committed to advancing the other clinical drug candidates in our pipeline and investing in our preclinical research programs. In HCV, we are planning on evaluating telaprevir in combination with VX-222, an investigational polymerase inhibitor that we obtained in 2009 through our acquisition of ViroChem, in a Phase 2a clinical trial that will involve a number of combination regimens. The objective of our ongoing clinical trials of HCV drug candidates and our earlier-stage activities with respect to potential treatments for HCV is to significantly improve the treatment options for genotype 1 HCV infection. The most advanced of our other drug candidates is VX-770, which we are evaluating in a registration program that focuses on patients with CF who have the G551D mutation in the gene responsible for CF. We also are planning on evaluating VX-770 in combination with VX-809 in a Phase 2a clinical trial in patients with the most common mutation in the gene responsible for CF. We have initiated a Phase 2a clinical trial of VX-509 in patients with moderate-to-severe RA and a Phase 2a clinical trial of VX-765 in patients with treatment-resistant epilepsy.

Drug Discovery and Clinical Development

        Discovery and development of a new pharmaceutical product is a difficult and lengthy process that requires significant financial resources along with extensive technical and regulatory expertise and can take 10 to 15 years or more. Throughout this entire process, potential drug candidates are subjected to rigorous evaluation, driven in part by stringent regulatory considerations, designed to generate information concerning efficacy, side-effects, proper dosage levels and a variety of other physical and chemical characteristics that are important in determining whether a drug candidate should be approved for marketing as a pharmaceutical product. Most chemical compounds that are investigated

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as potential drug candidates never progress into formal development, and most drug candidates that do advance into formal development never become commercial products. A drug candidate's failure to progress or advance may be the result of any one or more of a wide range of adverse experimental outcomes including, for example, the lack of sufficient efficacy against the disease target, the lack of acceptable absorption characteristics or other physical properties, difficulties in developing a cost-effective manufacturing or formulation method, or the discovery of toxicities or side-effects that are unacceptable for the disease indication being targeted or that adversely affect the competitive commercial profile of the drug candidate.

        Throughout the development process for a drug candidate we must work collaboratively with regulatory authorities, including the FDA, in order to identify the specific scientific issues that need to be addressed in the clinical trials to support continued development and approval of the drug candidate. If the data from our ongoing clinical trials or nonclinical studies regarding the safety or efficacy of a drug candidate are not favorable or regulatory authorities request additional clinical trials or changes to existing clinical trial protocols, we may be forced to delay or terminate the clinical development program for that candidate, which, particularly in the case of telaprevir, could materially harm our business.

        Because our investments are subject to considerable risks, we closely monitor the results of our clinical trials, discovery research and our nonclinical studies and frequently evaluate our portfolio investments in light of new data and scientific, business and commercial insights, with the objective of balancing risk and potential. This process can result in relatively abrupt changes in focus and priority as new information becomes available and we gain additional insights into ongoing programs and potential new programs. Although we believe that our development activities and the clinical trial data we have obtained regarding telaprevir have reduced the risks associated with obtaining regulatory approval, we cannot be sure that our development of telaprevir will lead to such regulatory approval of telaprevir or that such approval, if obtained, will occur in 2011. With respect to our other drug candidates, including VX-770, we have more limited data from clinical trials and nonclinical studies and as a result it is difficult to predict which, if any, of these drug candidates ultimately will result in pharmaceutical products.

Commercialization

        We plan to market telaprevir in North America, and we hold worldwide commercial rights to the other drug candidates in our pipeline. Over the past several years, we have expanded our commercial organization with a focus on building our understanding of the HCV market, developing our commercial strategy for the potential launch of telaprevir, and planning the infrastructure necessary to support future commercial activities. In the period prior to the anticipated launch of telaprevir, we will expand our commercial organization to an even more significant extent. This expansion will include implementation of internal systems and infrastructure in order to support commercial sales, incorporation of appropriate compliance policies and procedures, establishment of patient-focused programs and hiring a sales force to promote telaprevir, if approved, to health care providers. We are assembling a group of executives with broad experience in marketing, sales, distribution, and cost reimbursement of drugs. We will continue to build our commercial infrastructure by hiring a sales management team followed by a commercial sales force in the United States. If we obtain approval, we may market and sell one or more of our other drug candidates in markets outside North America, which would require additional expansion of our commercial organization.

Manufacturing

        We will require a supply of telaprevir for sale in North America and a supply of VX-770 for sale worldwide if we are successful in obtaining marketing approval for either or both of these drug candidates. We rely on an international network of third parties to manufacture and distribute our drug

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candidates for clinical trials, and we expect that we will continue to rely on third parties for the foreseeable future to meet our commercial supply needs for any of our drug candidates that are approved for sale. Third-party contract manufacturers, including some in Asia, supply us with raw materials, and contract manufacturers in the European Union and the United States convert these raw materials into drug substance, and convert the drug substance into final dosage form. Establishing and managing this global supply chain requires a significant financial commitment and the creation and maintenance of numerous third-party relationships. Although we attempt to effectively manage the business relationships with companies in our supply chain, we do not have complete control over their activities.

Corporate Collaborations

        Corporate collaborations have been and will continue to be an important component of our business strategy. Historically, we have not had the resources to develop and commercialize all of the drug candidates that we have identified or for which we have rights. Therefore we have relied on collaborations with third parties for the development and commercialization of some or all of our drug candidates. We have been successful in initiating productive collaborations with Janssen and Mitbsubishi Tanabe relating to telaprevir, and our collaboration with Cystic Fibrosis Foundation Therapeutics Incorporated contributed to the discovery of VX-770 and VX-809. Our early collaboration with GlaxoSmithKline plc resulted in two marketed drugs for the treatment of HIV. Collaborations continue to be an important part of our strategy going forward, although the structure and scope of available collaborative opportunities has changed in the past and may change in the future based on prevailing economic and competitive conditions.

Financing Strategy

        We have incurred losses from our inception and expect to continue to incur losses at least until we obtain approval for and successfully commercialize a product, if we ever do. Therefore, we have been dependent in large part on our ability to raise significant funding to finance our research and development operations, to create a commercial infrastructure, and to meet our overhead costs and long-term contractual commitments and obligations. To date, we have secured funds principally through capital market transactions, strategic collaborative agreements, investment income and the issuance of common stock under our employee benefit plans. As an element of our financial strategy we have from time to time transferred to third parties future financial rights under specific collaborations in exchange for one-time cash payments. For example, in 2009 we entered into two financial transactions that related to potential future milestone payments under our collaboration with Janssen that resulted in aggregate payments to us of $155.0 million. Also in 2009, we received a one-time cash payment of $105.0 million from Mitsubishi Tanabe and the right to a potential future milestone payment of up to $65.0 million, as part of an amendment to an existing agreement with Mitsubishi Tanabe. This amendment provided Mitsubishi Tanabe with a fully-paid license to commercialize telaprevir in Japan and specified other countries in the Far East and the right and obligation to manufacture telaprevir for sale in their territory. In 2008, for a one-time cash payment to us of $160.0 million, we sold our right to receive royalty payments, net of subroyalty amounts payable to a third party, arising from sales of Lexiva/Telzir and Agenerase under our 1993 agreement with GlaxoSmithKline.

        We expect that we will incur substantial expenses in order to complete the development and commercialization of telaprevir while at the same time continuing the development of our other drug candidates and building our other capabilities. As a result, we may raise additional capital in order to maintain adequate working capital and cash reserves to continue both our development and commercialization of telaprevir and our diversified research, discovery and development efforts. We expect we would need to raise additional capital if the development of telaprevir was materially delayed. We may raise additional capital from public offerings or private placements of our securities or

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other methods of financing. We cannot be sure that financing opportunities will be available on acceptable terms, if at all. If adequate funds are not available on acceptable terms, or at all, we may be required to significantly curtail or discontinue one or more of our research, drug discovery or development programs, including clinical trials, incur significant cash exit costs, or attempt to obtain funds through arrangements with collaborators or others that may require that we relinquish rights to certain of our drug candidates.

Critical Accounting Policies and Estimates

        Our discussion and analysis of our financial condition and results of operations is based upon our consolidated financial statements prepared in accordance with generally accepted accounting principles in the United States, or GAAP. The preparation of these financial statements requires us to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and the reported amounts of revenues and expenses during the reported periods. We monitor and analyze changes in facts and circumstances that might have a material effect on our estimates and assumptions in the future. Changes in estimates are reflected in reported results for the period in which they become known. We base our estimates on historical experience and various other assumptions that we believe to be reasonable under the circumstances. Actual results may differ from our estimates if past experience or other assumptions do not turn out to be substantially accurate.

        We believe that our application of the following accounting policies, each of which requires significant judgments and estimates on the part of management, are the most critical to aid in fully understanding and evaluating our reported financial results: business combinations; derivative instruments and embedded derivatives; revenue recognition; research and development expenses; restructuring expense; and stock-based compensation expense. Our accounting polices, including the ones discussed below, are more fully described in the Notes to our consolidated financial statements, including Note B "Accounting Policies," included in this Annual Report on Form 10-K.

Business Combinations

        In March 2009, we acquired ViroChem for $100.0 million in cash and common stock with a fair market value of $290.6 million. We assigned the value of the consideration transferred to acquire a business to the tangible assets and identifiable intangible assets acquired and liabilities assumed, on the basis of their fair values at the date of acquisition. The difference between the purchase price and the fair value of assets acquired and liabilities assumed was allocated to goodwill. This goodwill related to the potential synergies from the possible development of combination therapies involving telaprevir and the acquired drug candidates. The allocations recorded on our consolidated balance sheet as of the acquisition date included $525.9 million of intangible assets related to in-process research and development and a $162.5 million deferred tax liability. As of December 31, 2009, our consolidated balance sheet included $518.7 million of intangible assets related to in-process research and development and a $160.3 million deferred tax liability.

        The intangible assets acquired were in-process research and development assets relating to the drug candidates being developed by ViroChem, primarily VX-222 and VX-759, each of which was in Phase 1 clinical development at the date of acquisition. VX-222 and VX-759 had estimated fair values on the acquisition date of $412.9 million and $105.8 million, respectively. In addition, we considered ViroChem's other clinical drug candidates and determined that VCH-286, ViroChem's lead HIV drug candidate, had an estimated fair value on the acquisition date of $7.2 million, based on development costs through the acquisition date, and that the other clinical drug candidates had no fair value because the clinical and nonclinical data for those drug candidates did not support further development as of the acquisition date. We also considered ViroChem's preclinical programs and other technologies and determined that because of uncertainties related to the safety, efficacy and commercial viability of the potential drug candidates, market participants would not ascribe value to those assets.

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        We assess the fair value of assets, including intangible assets such as in-process research and development, using a variety of methods, including present-value models that are based upon multiple probability-weighted scenarios involving the development and potential commercialization of the acquired drug candidates. The present-value models used to estimate the fair values of VX-222 and VX-759 required us to make significant assumptions regarding the estimates market participants would make in evaluating a drug development asset, including the probability of successfully completing clinical trials and obtaining regulatory approval for marketing of the associated drug candidate, the timing of and the expected costs to complete in-process research and development projects, future cash flows from potential product sales, and appropriate discount rates. The estimated fair value ascribed to VX-222 and VX-759 was based on the estimated fair value that would be ascribed to each of these compounds by a market participant that acquired both compounds in a single transaction. The assumed probability of advancing VX-222 and VX-759 through various phases of development reflects the understanding among market participants that most drug candidates that enter Phase 2 clinical trials are not ultimately approved for commercial sale. While, on the date of acquisition, VX-222 and VX-759 were each at a similar stage of development, we attributed a significantly higher value to VX-222 than to VX-759 because the clinical and nonclinical data from the VX-222 research program was significantly more promising than the clinical and nonclinical data from the VX-759 research program. In addition, the fair value estimate incorporates our determination that a market participant would not be likely to continue development of VX-759 unless future data from clinical trials or nonclinical studies of VX-222 resulted in a delay or discontinuation of the VX-222 development program. Projections of the duration and cost of nonclinical studies and clinical trials vary significantly over the life of a project depending on developments in the program over time, but in order to estimate the fair market value on the acquisition date we made the following assumptions from the perspective of market participants regarding the potential timing and costs to develop VX-222 and/or VX-759. We assumed if a drug candidate were successfully developed in the United States it would take approximately five to nine years from the date of the acquisition in order to obtain marketing approval. In addition, for the valuation, we assumed an estimate of cost from acquisition to launch to develop a drug candidate that was within a range of $400 million to $700 million. Future cash flows, if any, would not be generated until a drug candidate completed all required phases of clinical trials and obtained regulatory approval. The risk-adjusted discount rate for each of these projects was approximately 28%.

        The in-process research and development assets were recorded at fair value and accounted for as indefinite-lived intangible assets. We maintain each of these assets on our consolidated balance sheet until either the research and development project underlying it is completed or the asset becomes impaired. If we complete a project, we will amortize the carrying value of the related intangible asset over the remaining estimated life of the asset. If we determine that a project has become impaired or we abandon a project, we will write down the carrying value of the related intangible asset to its fair value and will take an impairment charge in the period in which the impairment occurs. In order to complete an acquired research and development project, the related drug candidate must be evaluated in later-stage clinical trials, which are subject to all of the risks and uncertainties associated with the development of pharmaceutical products. If the fair value of any of these drug candidates, and in particular VX-222, becomes impaired as the result of unfavorable safety or efficacy data from any ongoing or future clinical trial or because of any other information regarding the prospects of successfully developing or commercializing the drug candidate, we could incur significant charges in the period in which the impairment occurs. VX-759, which is considered a backup compound to VX-222, could be impaired by data pertaining to the potential successful development of VX-222, which could result in significant charges in the period in which that data is analyzed and the determination is made. These intangible assets are tested for impairment on an annual basis as of October 1, or earlier if impairment indicators are present. Post-acquisition research and development expenses related to the in-process research and development projects will be expensed as incurred. In the fourth quarter of

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2009, we evaluated VX-222, VX-759, VCH-286 and goodwill for impairment. No impairment was found with respect to VX-222, VX-759 or goodwill. We recorded an impairment charge of $7.2 million related to VCH-286, which reduced the intangible assets reflected on our consolidated balance sheet by $7.2 million and also resulted in an adjustment to our deferred tax liability.

Derivative Instruments and Embedded Derivatives—September 2009 Financial Transactions

        In connection with the two financial transactions that we entered into in September 2009, we issued the 2012 Notes, which have a face value of $155.0 million and do not carry an explicit interest rate, for $122.2 million in cash. The 2012 Notes are secured by $155.0 million of potential future telaprevir milestone payments that we expect to receive from Janssen. We also sold $95.0 million in additional potential future telaprevir milestone payments that we expect will be payable by Janssen for a cash payment of $32.8 million. The 2012 Notes contain an embedded derivative related to their potential early repayment or redemption. The separate sale of the potential $95.0 million in future milestone payments is accounted for as a free-standing derivative instrument.

        In order to account for the 2012 Notes and the sale of the rights to the potential future milestone payments, we were required to estimate the fair value of the derivative embedded in the 2012 Notes and of the derivative associated with the $95.0 million in potential future milestone payments. The models we used to estimate these fair values require, among other things, estimates of the assumptions market participants would make regarding the timing and probability of achieving the milestones and the appropriate discount rates. In the fourth quarter of 2009, we recorded interest expense of $3.1 million related to the 2012 Notes and an additional net expense of $1.8 million related to the changes in estimated fair value of the derivative related to the $95.0 million in potential future milestone payments and the derivative embedded in the 2012 Notes.

2012 Notes

        The 2012 Notes had a residual value at issuance of $108.2 million, excluding the fair value of the embedded derivative. That embedded derivative had a fair value at issuance of $10.7 million. We record a quarterly interest expense with respect to the 2012 Notes that is determined using the effective interest rate method, which increases the amount of the liability for our 2012 Notes each quarter by an amount corresponding to this interest expense through the stated maturity date, unless redeemed or repaid earlier. In addition, we evaluate the embedded derivative for changes in fair value on at least a quarterly basis. As of December 31, 2009, the value of the 2012 Notes was $111.3 million and the fair value of the embedded derivative was $10.5 million. We expect that the net expense related to the 2012 Notes that we will recognize based on interest expense and gains and losses on the embedded derivative over the period between December 31, 2009 and October 31, 2012 will equal $33.2 million, which is the difference between the $155.0 million face value of the 2012 Notes and the fair value of the 2012 Notes with their embedded derivative on December 31, 2009. However, the timing of these expenses or any gains will depend on a number of factors, including factors related to the probability and timing of achieving the relevant milestone events and to applicable discount rates, and could result in material expenses or gains in any quarterly period.

Sale of Future Milestone Payments

        The fair value on the sale date of the free-standing derivative instrument created by the sale of $95.0 million of future milestone rights was $36.2 million. As of December 31, 2009, the fair value of the free-standing derivative was $38.2 million. We will evaluate this free-standing derivative for changes in fair value on at least a quarterly basis. Any change in the fair value will be recorded as a loss or gain in the period in which it becomes known. If these milestone events are achieved, we expect that we will recognize net expenses over the period between December 31, 2009 and the date the milestones are achieved equal to $56.8 million, which is the difference between the $95.0 million the purchaser will

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receive if all the milestone events are achieved and the fair value of the free-standing derivative on December 31, 2009. Because our estimate of the fair value of the free-standing derivative includes the application of a discount rate, we expect to record costs to reflect the time-value of money each quarter. However, the timing of any other expenses or any gains will depend on a number of factors, including, among other things, factors related to the probability and timing of achieving the relevant milestone events and to applicable discount rates, and could result in material losses or gains in any quarterly period.

Revenue Recognition

        Our revenues are generated primarily through collaborative research, development and/or commercialization agreements. The terms of these agreements typically include payment to us of one or more of the following: nonrefundable, up-front license fees; milestone payments; and royalties on product sales. In addition, we sold our rights to receive future royalties from our HIV assets and have been recognizing revenues in connection with that transaction since the date of the sale in May 2008.

Up-front License Fees

        We recognize revenues from nonrefundable, up-front license fees related to collaboration agreements, including the $165.0 million we received from Janssen in 2006 and the $105.0 million we received from Mitsubishi Tanabe in the third quarter of 2009, on a straight-line basis over the contracted or estimated period of performance. The period of performance over which the revenues are recognized is typically the period over which the research and/or development is expected to occur. As a result, we often are required to make estimates regarding drug development and commercialization timelines for compounds being developed pursuant to a collaboration agreement. Because the drug development process is lengthy and our collaboration agreements typically cover activities over several years, this approach often has resulted in the deferral of significant amounts of revenue into future periods. In addition, we periodically evaluate our estimates in light of changes in the development plans for our drug candidates. Because of the many risks and uncertainties associated with the development of drug candidates, our estimates regarding the period of performance have changed in the past and may change in the future. Our estimates regarding the period of performance under the Janssen collaboration agreement were adjusted in 2007, and again in the third quarter of 2009, as a result of changes in the global development plan for telaprevir, which contemplates the conduct of certain development activities in the post-approval period if telaprevir is approved for marketing. These adjustments were made on a prospective basis beginning in the periods in which the changes were identified. These adjustments resulted in a decrease in the amount of revenues we recognized from the Janssen collaboration by $2.6 million per quarter for the first adjustment and by $1.1 million per quarter for the second adjustment. Any future adjustment in our estimates of the period of performance under any of our collaborations could result in substantial changes to the period over which the revenues from an up-front license fee related to that collaboration are recognized. For example, if we adjust our estimates as of January 1, 2010 to increase the period of performance under the Janssen agreement by one year, it would result in a decrease in the amount of deferred revenues we recognize from our Janssen collaboration of $0.8 million per quarter beginning in the first quarter of 2010.

Milestone Payments

        At the inception of each agreement that includes contingent milestone payments, we evaluate whether the contingencies underlying each milestone event are substantive, specifically reviewing factors such as the scientific and other risks that must be overcome to achieve the milestone event, as well as the level of successful effort and investment required. If we do not consider a milestone event to be substantive, the revenues from the related milestone payment cannot be recognized when the milestone

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event is achieved, but must be recognized on a straight-line basis over the remaining performance period.

        Where a substantive milestone event is achieved in a collaboration arrangement and the corresponding payment is reasonably assured, the payment is recognized as earned subject to specific policies applicable where we have obligations remaining after achievement of the milestone. Because achievement of a substantive milestone event under a collaboration agreement typically requires the completion of a number of activities conducted over a significant period of time, the expenses related to achieving the milestone event often are incurred prior to the period in which the milestone payment is recognized. All of the milestones that have been achieved under our Janssen collaboration agreement during the three years ended December 31, 2009 have been considered substantive. In the past, significant quarterly and annual fluctuations in our revenues from milestone payments have contributed to significant fluctuations in our overall collaborative revenues.

Royalty Revenues

        In May 2008, we entered into a purchase agreement with Fosamprenavir Royalty, L.P. pursuant to which we sold, and Fosamprenavir Royalty purchased for a one-time cash payment to us of $160.0 million, our right to receive royalty payments, net of subroyalty amounts payable to a third party, arising from sales of Lexiva/Telzir and Agenerase under our 1993 agreement with GlaxoSmithKline. We deferred the recognition of $155.1 million of revenues in connection with this sale. On May 31, 2008, we began recognizing these deferred revenues under the units-of-revenue method. Under this method, the amount of deferred revenues to be recognized as royalty revenues in each period is calculated by multiplying the following: (1) the net royalty payments due from GlaxoSmithKline to Fosamprenavir Royalty for the period by (2) the ratio of the revenues we received from the sale of our rights to HIV royalty payments that we have not yet recognized to the total estimated remaining net royalties that we expect GlaxoSmithKline to pay Fosamprenavir Royalty over the remaining term of the agreement. Estimating the total remaining net royalties that GlaxoSmithKline will pay to Fosamprenavir Royalty requires the use of subjective estimates and assumptions, including estimates regarding the size of the potential market for HIV protease inhibitors, the competitive position of Lexiva/Telzir specifically and HIV protease inhibitors generally with respect to currently approved drugs and drugs that may be approved in the future, and the pricing of Lexiva/Telzir. Changes to our estimate of the total remaining net royalties that GlaxoSmithKline will pay to Fosamprenavir Royalty could have a material effect on the amount of royalty revenues we recognize in a particular period.

        Prior to May 2008, royalty revenues typically were recognized based upon actual and estimated net sales of licensed products in licensed territories and generally were recognized in the period the sales occurred. We reconciled and adjusted for differences between actual royalty revenues and estimated royalty revenues in the quarter any differences became known. These differences were not significant.

Research and Development Expenses

        All research and development expenses, including amounts funded through research and development collaborations, are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salary and benefits; stock-based compensation expense; laboratory supplies and other direct expenses; contractual services, including clinical trial and pharmaceutical development costs; expenses associated with the commercial supply investment in our drug candidates, which are considered research and development expenses due to the drug candidates' stages of development; and infrastructure costs, including facilities costs and depreciation.

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        When third-party service providers' billing terms do not coincide with our period-end, we are required to make estimates of our obligations to those third parties, including clinical trial and pharmaceutical development costs, contractual services and costs for commercial supply of our drug candidates, incurred in a given accounting period and record accruals at the end of the period. We base our estimates on our knowledge of the research and development programs, services performed for the period, past history for related activities and the expected duration of the third-party service contract, where applicable.

        We are incurring significant costs related to commercial supplies of telaprevir, which entered into Phase 3 development in the first quarter of 2008. We also are beginning to incur costs related to commercial supplies of VX-770, although these have been considerably less than the costs related to commercial supplies of telaprevir. After a drug candidate enters into Phase 3 clinical development, determining whether to continue to classify all of these costs as research and development expenses or to capitalize some of them as inventory involves significant judgments. Generally, inventory may be capitalized if it is probable that future revenues exceeding the costs of the inventory will be generated from the sale of the inventory. While we believe that the development activities and clinical trial data to date have reduced the risks associated with obtaining marketing approval for telaprevir, for accounting purposes we continue to expense all of our costs related to commercial supplies of telaprevir because of the inherent risks of drug development. To the extent that we continue to consider these costs as research and development expenses as we continue development of telaprevir, we expect that if and when we receive marketing approval for telaprevir the costs of our initial commercial supplies of telaprevir will have already been expensed. A consequence of the application of this accounting policy is that during the initial period after the potential launch of telaprevir our cost of goods sold will not reflect costs recorded as research and development expenses in prior periods.

Restructuring Expense

        We record liabilities associated with restructuring activities based on estimates of fair value in the period the liabilities are incurred. The liability for accrued restructuring expense of $34.0 million at December 31, 2009 is related to that portion of our facility in Kendall Square, Cambridge, Massachusetts that we are not occupying and do not intend to occupy. This liability is calculated by applying our best estimate of the net amount of our ongoing obligation. We use a discounted cash-flow analysis to calculate the amount of this liability. The probability-weighted discounted cash-flow analysis is based on management's assumptions and estimates of our ongoing lease obligations, including contractual rental commitments, build-out commitments and building operating costs, and estimates of income from subleases, based on the term and timing of the subleases. We discount the estimated cash flows using a discount rate of approximately 10%. These cash flow estimates are reviewed and may be adjusted in subsequent periods. Adjustments are based, among other things, on management's assessment of changes in factors underlying the estimates. Because our estimate of the liability includes the application of a discount rate to reflect the time-value of money, the estimate will increase simply as a result of the passage of time, even if all other factors remain unchanged.

        Our estimates of our restructuring liability have changed in the past, and it is possible that our assumptions and estimates will change in the future, resulting in additional adjustments to the amount of the estimated liability. The effect of any such adjustments could be material. For example, we currently have two subleases for portions of the Kendall Square facility with remaining terms of one and three years, respectively, and we have made estimates and assumptions relating to future sublease terms following the expiration of the current subleases. Market variability may require adjustments to those assumptions in the future. We will review our assumptions and judgments related to the lease restructuring on at least a quarterly basis until the Kendall Square lease is terminated or expires, and make whatever modifications we believe are necessary, based on our judgments, to reflect any changed circumstances.

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Stock-based Compensation Expense

        We measure the compensation cost of stock-based compensation at the grant date, based on the fair value of the award, including estimated forfeitures, and we recognize that cost as an expense ratably over the associated employee service period, which generally is the vesting period of the equity award, or the derived service period for awards with market conditions. For our awards with performance conditions, we make estimates regarding the likelihood of satisfaction of the performance condition which affect the period over which the expense is recognized. We calculate the fair value of stock options and shares purchased pursuant to the Employee Stock Purchase Plan using the Black-Scholes option pricing model. The Black-Scholes option pricing model requires us to make certain assumptions and estimates concerning our stock price volatility, the rate of return of risk-free investments, the expected term of the awards, and our anticipated dividends. In determining the amount of expense to be recorded, we also are required to exercise judgment to estimate forfeiture rates for awards, based on the probability that employees will complete the required service period. If actual forfeitures differ significantly from our estimates, if any of our estimates or assumptions prove incorrect, or if the likelihood of achievement of a performance condition changes, our results could be materially affected.

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RESULTS OF OPERATIONS

Net Loss

        In 2009 as compared to 2008, our net loss increased by $182.3 million, or 40%. The increased net loss in 2009 as compared to 2008 was the result of significant increases in our costs and expenses combined with significant decreases in our revenues. Our lower revenues in 2009 were primarily the result of our receipt and recognition of milestone payments in 2008 for which there were no corresponding milestone payments in 2009. The increased expenses included increased operating expenses related to the growth in size of our workforce and to our late-stage clinical programs and increased stock-based compensation expense. We currently expect that our net loss for 2010 will exceed our net loss for 2009, primarily as a result of activities to prepare for the potential commercial launch of telaprevir in 2011.

        In 2008 as compared to 2007, our net loss increased by $68.6 million, or 18%. The increased net loss in 2008 as compared to 2007 was the result of a combination of factors, including lower revenues from royalties as a result of the sale of our HIV royalty stream and decreases in revenues from our collaborations, an increase in our overall expenses and a decrease in our net interest income as a result of lower yields on invested funds and higher levels of outstanding debt. In 2008, we increased our workforce, particularly in our development and commercialization organizations, leading to increased employee-related expenses. In 2008, these increased expenses, as compared to 2007, were largely offset by decreased expenses related to our commercial supply investment in telaprevir, resulting in an overall 3% increase in our operating costs and expenses.

Net Loss Per Share

        Our net loss for 2009 was $3.71 per basic and diluted common share compared to a net loss for 2008 of $3.27 per basic and diluted common share. Our net loss per basic and diluted common share increased in 2009 from 2008 as a result of a 40% increase in net loss, partially offset by an increase in the number of basic and diluted weighted-average common shares outstanding from 140.6 million shares in 2008 to 173.3 million shares in 2009.

        Our net loss for 2008 was $3.27 per basic and diluted common share compared to a net loss for 2007 of $3.03 per basic and diluted common share. Our net loss per basic and diluted common share increased in 2008 from 2007 as a result of an 18% increase in net loss, partially offset by an increase in the number of basic and diluted weighted-average common shares outstanding from 129.0 million shares in 2007 to 140.6 million shares in 2008.

Stock-based Compensation and Certain Other Expenses

        The comparison of our operating costs and expenses and other losses in the three years ended December 31, 2009, and particularly the comparison between 2009 and 2008, is affected by increases in our stock-based compensation expense in 2009 as well as expenses and an impairment of intangible

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assets related to our acquisition of ViroChem, and the loss on exchanges of a portion of the 2013 Notes for our common stock in 2009.

Revenues

        Our total revenues in recent periods have been comprised primarily of collaborative revenues, which decreased in both 2009 and 2008 in comparison with the preceding year. On a quarterly and annual basis our collaborative revenues have fluctuated significantly, due to the timing of recognition of significant milestone payments. In 2010, we expect to recognize approximately $75 million of deferred revenues currently reflected on our consolidated balance sheet and additional collaborative revenues from our collaborative relationships and other sources. We do not expect to have any revenues from the sale of telaprevir in 2010. If we are able to successfully commercialize telaprevir in accordance with current development timelines, product revenues from the sales of telaprevir would commence in 2011.

Collaborative Revenues

        The table presented below is a summary of revenues from collaborative arrangements for 2009, 2008 and 2007:

        Our revenues from the Janssen collaboration in each period consist of:

•

development milestone payments, if any, recognized in the period;



•

net reimbursements from Janssen for development costs of telaprevir,



•

sales of materials, if any, to Janssen in the period; and



•

an amortized portion of the $165.0 million up-front payment received from Janssen in 2006.

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Amounts that Janssen pays us for reimbursement of our telaprevir clinical development expenses, after we offset reimbursement amounts owed by us to Janssen for reimbursements of Janssen's telaprevir clinical development expenses, are recorded as revenues.

        The $65.5 million, or 55%, decrease in our revenues from Janssen in 2009 compared to 2008 was primarily the result of a decrease in milestone revenues. We recognized a total of $55.0 million from the achievement of milestones in 2008 for which there were no corresponding milestones achieved in 2009. The $55.0 million in milestone revenue from the Janssen collaboration in 2008 was an increase of $25.0 million in comparison to 2007. In the third quarter of 2009, we entered into two financial transactions related to $250.0 million in potential future milestone payments related to the regulatory filing with and approval of telaprevir by the European Medicines Evaluation Agency, and the launch of telaprevir in the European Union. If Janssen is able to successfully commercialize telaprevir in accordance with current development timelines, we anticipate these milestones will be earned prior to April 2012. We expect that, when and if earned, these milestones will result in collaborative revenues of which the proceeds from the first $155.0 million would be used to redeem the 2012 Notes and the remaining $95.0 million would be paid by Janssen to the purchaser of these milestones.

        In 2009, our collaborative revenues from sources other than Janssen primarily related to our collaboration with Mitsubishi Tanabe. On July 30, 2009, we entered into an amendment to our license, development and commercialization agreement with Mitsubishi Tanabe that provided for a $105.0 million payment in connection with the execution of the amendment. This payment was initially classified as deferred revenues and is being recognized over our expected period of performance. In 2009, we recognized a total of $18.7 million of revenues from Mitsubishi Tanabe, including the amortized portion of the $105.0 million up-front payment. In 2008, our collaborative revenue from sources other than Janssen primarily related to $9.9 million of revenue from Mitsubishi Tanabe relating to reimbursements for development costs, milestone payments and the sale of materials to Mitsubishi Tanabe, and the $6.0 million milestone we achieved pursuant to our collaboration with Merck, for which there was no corresponding milestone payment in 2009.

        The decrease in our total collaborative revenues from sources other than Janssen in 2008 as compared to 2007 was primarily attributable to decreased revenues from our collaboration with CFFT. In early 2008, we completed our reimbursable activities under our collaboration with CFFT, which resulted in the $15.1 million decrease in revenues from this collaboration in 2008 as compared to 2007.

Royalty Revenues