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 an oral hepatitis C protease inhibitor and one of the most advanced of a new class of antiviral treatments in clinical development that targets hepatitis C virus, or HCV, infection. Telaprevir is being evaluated in a fully-enrolled registration program focused on treatment-naïve and treatment-failure patients with genotype 1 HCV. We currently intend to submit a new drug application, or NDA, for telaprevir in the United States in the second half of 2010, assuming the successful completion of the registration program. We also are developing, among other compounds, VX-770 and VX-809, drug candidates for the treatment of patients with cystic fibrosis, or CF, and VX-509, a Janus kinase 3, or JAK3, inhibitor designed for the treatment of immune-mediated inflammatory diseases including rheumatoid arthritis. In the second quarter of 2009, we began a registration program for VX-770 that focuses on patients with CF who have the G551D mutation in the gene responsible for CF. We intend to continue investing in our research programs with the goal of adding to our pipeline drug candidates designed to address significant unmet medical needs and provide substantial benefits to patients.

Business Focus

Over the upcoming years, we expect to focus a substantial portion of our resources on the development and commercialization of telaprevir. Our clinical development program is designed to support registration by us of telaprevir in North America for treatment-naïve and treatment-failure patients with genotype 1 HCV, and by our collaborators, Janssen Pharmaceutica, N.V., a Johnson & Johnson company, and Mitsubishi Tanabe Pharma Corporation, in international markets.

In the second quarter of 2009, we initiated a registration program for VX-770 focused on patients with CF who have the G551D mutation. We also expect to continue the development of VX-809, an investigational corrector compound that is being evaluated in a Phase 2a clinical trial in patients with CF. As a result, we expect that over the next several years we will need to substantially increase resources focused on the development of our CF drug candidates. We plan to leverage the infrastructure that we are building in preparation for the potential launch of telaprevir to support the potential launch of VX-770.

In addition to the registration programs for telaprevir and VX-770, 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. We believe that meaningful information will be provided by ongoing and planned Phase 2 clinical trials for a number of our earlier-stage drug candidates, including a planned combination clinical trial in patients with HCV of telaprevir with VX-222, our recently acquired HCV polymerase inhibitor, ongoing and planned Phase 2 clinical trials of VX-809 in patients with the most common CF mutation, and a planned Phase 2a clinical trial of VX-509 in patients with moderate to severe rheumatoid arthritis, allowing us to make decisions regarding future development activities in these programs.

Drug Discovery and Clinical Development

Discovery and development of a new pharmaceutical product is a lengthy and resource-intensive process, which may 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. The toxicity characteristics and profile of drug candidates at varying dose levels administered for varying periods of time also are monitored

and evaluated during the nonclinical and clinical development process. Most chemical compounds that are investigated 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 treated or that adversely affect the competitive commercial profile of the drug candidate.

Designing, coordinating and conducting large-scale clinical trials to determine the efficacy and safety of drug candidates and to support the submission of an NDA requires significant financial resources, along with extensive technical and regulatory expertise and infrastructure. Prior to commencing a late-stage clinical trial of any drug candidate, we must work collaboratively with regulatory authorities, including the United States Food and Drug Administration, or FDA, in order to identify the specific scientific issues that need to be addressed by the clinical trials in order to support continued development and approval of the drug candidate. These discussions with regulatory authorities typically occur over a period of months and can result in significant changes to planned clinical trial designs or timelines. In addition, even after agreement with respect to a clinical trial design has been reached, regulatory authorities may request additional clinical trials or changes to existing clinical trial protocols. If the data from our ongoing clinical trials or nonclinical studies regarding the safety or efficacy of our drug candidates are not favorable, we may be forced to delay or terminate the clinical development program, which, particularly in the case of telaprevir, would materially harm our business. Further, even if we obtain marketing approvals from the FDA and comparable foreign regulatory authorities in a timely manner, we cannot be sure that the drug will be commercially successful.

Our investments are subject to the considerable risk that one or more of our drug candidates will not progress to product registration due to a wide range of adverse experimental outcomes. We 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 is analyzed 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 to date have reduced the risks associated with obtaining marketing approval for telaprevir, we cannot be sure that our development of telaprevir will lead successfully to regulatory approval of telaprevir on a timely basis, or at all, or that obtaining regulatory approval will lead to commercial success of telaprevir. With respect to our other drug candidates, 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 will result in pharmaceutical products.

Drug Candidates

Telaprevir, our oral HCV protease inhibitor, is being investigated in a registration program focused on patients with genotype 1 HCV that includes ADVANCE and ILLUMINATE, which are Phase 3 clinical trials in treatment-naïve patients, and REALIZE, which is a Phase 3 clinical trial in treatment-failure patients. Enrollment in ADVANCE, ILLUMINATE and REALIZE was completed in October 2008, January 2009 and February 2009, respectively. Telaprevir dosing is complete in all three of these Phase 3 clinical trials. We expect to have sustained viral response, or SVR, data from the ADVANCE

and ILLUMINATE clinical trials in the first half of 2010 and SVR data from the REALIZE clinical trial in mid-2010. We currently intend to submit an NDA for telaprevir in the second half of 2010, assuming the successful completion of our ongoing registration program. In addition to the clinical trials in our registration program, several additional clinical trials are being conducted by us and our collaborators.

The successful development and commercialization of telaprevir is critical to the success of our business as currently conducted. While we are devoting significant resources, time and attention to the development, potential regulatory approval and a successful commercial launch of telaprevir, all of these efforts involve significant scientific and execution risks and can be adversely affected by events, such as competitive activities, adverse trial results and regulatory actions, outside of our direct control.

We have completed three Phase 2b clinical trials of telaprevir-based combination therapy in patients with genotype 1 HCV, which enrolled an aggregate of approximately 580 treatment-naïve patients and 440 patients who did not achieve an SVR with a previous treatment with pegylated-interferon, or peg-IFN, and ribavirin, or RBV. The SVR rates on an intent-to-treat basis of the patients in the 24-week telaprevir-based treatment arms and the control arms of PROVE 1 and PROVE 2, the two Phase 2b clinical trials that evaluated treatment-naïve patients, are set forth in the table below:

                                                                  PROVE 1     PROVE 2
24-week telaprevir-based treatment arm:
   telaprevir in combination with peg-IFN and RBV for
   12 weeks, followed by peg-IFN and RBV alone for 12 weeks             61 %        69 %
48-week control arm:
   48 weeks of therapy with peg-IFN and RBV                             41 %        46 %

The SVR rates of the patients on an intent-to-treat basis in the 24-week telaprevir-based triple-therapy treatment arm, the 48-week telaprevir-based treatment arm and the control arm of PROVE 3, the Phase 2b clinical trial that evaluated treatment-failure patients, are set forth in the table below:

                          Non-responders      Relapsers      Breakthroughs         Total
24-week
telaprevir-based
triple-therapy
treatment arm:
   telaprevir in
   combination with
   peg-IFN and RBV for
   12 weeks, followed
   by peg-IFN and RBV
   alone for 12 weeks          39% (n=66)      69% (n=42)          57% (n=7)     51% (n=115)
48-week
telaprevir-based
treatment arm:
   telaprevir in
   combination with
   peg-IFN and RBV for
   24 weeks, followed
   by peg-IFN and RBV
   alone for 24 weeks          38% (n=64)      76% (n=41)          50% (n=8)     52% (n=113)
48-week control arm:
   48 weeks of therapy
   with peg-IFN and
   RBV                          9% (n=68)      20% (n=41)          40% (n=5)     14% (n=114)

The adverse event profile of telaprevir generally has been consistent across our Phase 2 clinical trials, which have principally involved clinical trial sites in North America and Europe. Safety data from our Phase 2 clinical trials indicated that the most common adverse events, regardless of treatment assignment, were fatigue, rash, headache and nausea. The most common adverse events reported more frequently in patients receiving telaprevir than in the control arms were gastrointestinal events, skin events-rash and pruritus-and anemia. There have been reports of severe rashes in clinical trials involving telaprevir-based treatments, including several reports from the clinical trials being conducted by Mitsubishi Tanabe in Japan, where telaprevir has advanced into Phase 3 clinical trials in combination with peg-IFN and RBV. Rash resulted in treatment discontinuations in the telaprevir-based treatment arms in approximately 7% of patients in PROVE 1 and PROVE 2 and 5% of patients in PROVE
3. Other adverse events reported in our Phase 2 clinical trials generally were similar in type and frequency to those seen with peg-IFN and RBV treatment.

In October 2009, we announced data from the C208 trial, which was an exploratory open-label clinical trial that enrolled 161 treatment-naïve patients infected with genotype 1 HCV. The purpose of the C208 trial was to compare twice-daily dosing regimens of telaprevir-1,125 mg every 12 hours-in combination with peg-IFN and RBV, with three-times daily dosing regimens-750 mg every 8 hours-in combination with peg-IFN and RBV. A three-times daily dosing regimen is being used in the ongoing registration program for telaprevir and has also been used in the other clinical trials for telaprevir.

Patients received telaprevir, peg-IFN and RBV for 12 weeks followed by an additional 12 or 36 weeks of peg-IFN and RBV alone in a response-guided trial design. Patients who achieved undetectable HCV RNA-<25 IU/mL, undetectable per Roche COBAS TaqMan HCV test-at week 4, which is referred to as a rapid viral response, or RVR, and who maintained undetectable HCV RNA through week 20, were able to stop all treatment after 24 weeks. Patients who did not meet the response-guided criteria received a total of 48 weeks of peg-IFN and RBV therapy. 18% of patients across the treatment arms were required to continue treatment for 48 weeks.

The following table summarizes the RVR and SVR data on an intent-to-treat basis from the C208 trial.

                                                                              SVR
                                                              RVR        (undetectable
                                              Total      (undetectable   24 weeks after
                          Combination        Number      at week 4 on       end-of-
 Telaprevir Dosing          Therapy        of Patients    treatment)       treatment)
 1,125 mg every             alfa-2a
 12 hours                (PEGASYS)/RBV         40         83% (n=33)       83% (n=33)
 1,125 mg every             alfa-2b
 12 hours               (PEGINTRON)/RBV        39         67% (n=26)       82% (n=32)
 750 mg every               alfa-2a
 8 hours                 (PEGASYS)/RBV         40         80% (n=32)       85% (n=34)
 750 mg every               alfa-2b
 8 hours                (PEGINTRON)/RBV        42         69% (n=29)       81% (n=34)

The frequency and severity of adverse events and the rate of treatment discontinuations were similar to those reported in prior telaprevir trials. The most common adverse events reported in patients in this clinical trial were pruritis, nausea, rash, anemia, flu-like illness, fatigue and headache, and the adverse events were similar overall between the patient groups receiving three-times daily dosing and those receiving twice-daily dosing. Serious adverse events leading to permanent treatment discontinuation of all drugs occurred in 5% of patients and were mainly related to rash, which resulted in discontinuation of 4 out of 161, or 3%, of patients and anemia, which resulted in discontinuation of 3 out of 161, or 2%, of patients.

In October 2009, we also announced interim data from a clinical trial, referred to as the 107 Trial, in patients who did not achieve an SVR in the control arms of the PROVE 1, PROVE 2 or PROVE 3 clinical trials. In the open-label 107 Trial, treatment-experienced patients with genotype 1 HCV were

treated with telaprevir triple combination therapy for 12 weeks followed by 12 or 36 weeks of treatment with peg-IFN and RBV alone. In 2008, the protocol for the 107 Trial underwent several amendments, including important amendments that affected prior null-responders.

The table below sets forth the interim data from 94 of the 117 patients enrolled in the 107 Trial, including SVR data and data regarding patients who relapsed in the 24 weeks after end-of-treatment.

                                                                         Viral Relapse
Patient Group                Treatment Regimen                 SVR           Rates
Prior Null          telaprevir triple combination for      57% (16/28)    20% (4/20)
Responders          12 weeks, followed by peg-IFN and
                    RBV alone for 36 weeks
Prior Partial       25 patients treated with telaprevir    55% (16/29)    22% (5/23)
Responders          triple combination therapy for
                    12 weeks, followed by peg-IFN and
                    RBV alone for 12 weeks
                    3 patients treated with telaprevir
                    triple combination therapy
                    combination for 12 weeks, followed
                    by peg-IFN and RBV alone for
                    36 weeks
                    1 patient who discontinued prior to
                    completing 12 weeks of telaprevir
                    triple combination therapy
Prior Relapsers     25 patients treated with telaprevir    90% (26/29)     4% (1/28)
                    triple combination therapy for
                    12 weeks, followed by peg-IFN and
                    RBV alone for 12 weeks
                    3 patients treated with telaprevir
                    triple combination therapy for
                    12 weeks, followed by peg-IFN and
                    RBV alone for 36 weeks
                    1 patient who discontinued prior to
                    completing 12 weeks of telaprevir
                    triple combination therapy
Prior Viral         7 patients treated with telaprevir      75% (6/8)      0% (0/6)
Breakthroughs       triple combination therapy for
                    12 weeks, followed by peg-IFN and
                    RBV alone for 12 weeks
                    1 patient treated with telaprevir
                    triple combination therapy for
                    12 weeks, followed by peg-IFN and
                    RBV alone for 36 weeks

The interim results reported in the table above reflect data from all prior partial responders, relapsers and viral breakthroughs and from the prior null responders who we considered to have received an appropriate treatment regimen based on their prior response to peg-IFN and RBV, consistent with certain amendments made during the conduct of the 107 Trial. The table does not include data from 23 prior null responders, who, prior to protocol amendments, were designated to receive only 24 weeks of therapy, and a portion of whom met the strict stopping rule criteria at week 4 that were in effect at that time. When the 107 Trial began, all patients were to receive 12 weeks of telaprevir in combination with peg-IFN and RBV followed by an additional 12 weeks of peg-IFN and RBV. Stopping rules required any patient who did not achieve undetectable HCV RNA by week 4 to stop all treatment. In 2008, the 107 Trial protocol was amended in several respects. The most important change to the protocol was to the week 4 stopping rules, as it became evident that treatment-failure patients had a somewhat slower viral response to treatment with telaprevir triple-combination therapy than did treatment-naïve patients. Therefore, following the protocol amendment patients who had detectable HCV RNA at week 4 were permitted to continue therapy. In addition, while the initial study protocol specified 24 weeks of total treatment for all patients, a longer total treatment duration of 48 weeks was determined to be warranted in prior null responders to provide a higher likelihood of achieving an SVR.

Discontinuation of all therapy due to adverse events occurred in eight patients in the 107 Trial. A complete safety analysis is still being performed and will be reported when the full data are presented at a medical conference expected in 2010.

HCV polymerase inhibitors, including our HCV polymerase inhibitors VX-222 (formerly VCH-222) and VX-759 (formerly VCH-759), are direct-acting antivirals that inhibit the ability of the HCV to replicate through a mechanism distinct from HCV protease inhibitors such as telaprevir. VX-222 and VX-759 were evaluated by ViroChem Pharma, Inc., or ViroChem, in Phase 1 clinical trials prior to our acquisition of ViroChem in March 2009. In a Phase 1 viral kinetics clinical trial involving five treatment-naïve patients with genotype 1 HCV infection, VX-222 dosed at 750 mg twice daily resulted in a median 3.7 log10 decrease in HCV RNA-equivalent to a 5,000-fold reduction in virus in the blood-at the end of three days of dosing. The results were consistent from patient to patient, and across HCV genotype 1 subtypes. In clinical evaluations of VX-222 to date, no serious adverse events have been observed.

We are conducting a multi-dose viral kinetics clinical trial to evaluate the antiviral activity, safety, tolerability and pharmacokinetics of VX-222 in patients with genotype 1 HCV infection. This ongoing multi-dose clinical trial of VX-222 will evaluate the antiviral activity of VX-222 dosed as monotherapy for three days in approximately 32 treatment-naïve patients with HCV genotype 1 infection. We also are conducting a drug-drug interaction clinical trial of VX-222 and telaprevir in healthy volunteers. We expect data from these clinical trials in the fourth quarter of 2009, which could enable the initiation of a combination trial of telaprevir and VX-222 in patients with genotype 1 HCV as early as the fourth quarter of 2009, depending on the trial results. There currently are no ongoing clinical trials of VX-759.

In May 2009, we initiated a registration program, referred to as ENDEAVOR, for VX-770, which is an investigational cystic fibrosis transmembrane conductance regulator, or CFTR, potentiator that targets the defective CFTR protein that causes CF. The VX-770 registration program focuses on patients with the G551D mutation, which is present in approximately 4% of the CF population in the United States. ENDEAVOR consists of three clinical trials, which have opened for enrollment.

The primary clinical trial, which is referred to as STRIVE, is a Phase 3 clinical trial of VX-770 in patients 12 years and older with the G551D mutation on at least one of the patient's two CFTR genes, or alleles. We expect STRIVE to be fully enrolled in the first quarter of 2010. The second clinical trial, which is referred to as ENVISION, is a two-part Phase 3 clinical trial of VX-770 in patients between 6 to 11 years of age with the G551D mutation on at least one allele. The third clinical trial, which is referred to as DISCOVER, is a Phase 2 exploratory clinical trial of VX-770 in patients with CF who are 12 years and older and homozygous for the F508del mutation. The DISCOVER clinical trial opened to patient enrollment in the third quarter of 2009.

In October 2008, we completed a Phase 2a clinical trial of VX-770 in 39 patients with CF with the G551D mutation. Patients in the Phase 2a clinical trial received VX-770 over 14-day and 28-day dosing periods. The primary endpoint for this clinical trial was safety, and no serious adverse events attributable to VX-770 were observed. The promising lung function data from this Phase 2a clinical trial, as measured by improvements in FEV1, and the observed changes in biomarkers that seek to measure the activity of the CFTR protein, were used to design the ENDEAVOR registration program.

We have conducted Phase 1 clinical trials of VX-809, a CFTR corrector compound, in healthy volunteers and an escalating single-dose pharmacokinetics and safety clinical trial of VX-809 in patients with CF who carry the F508del mutation on the CFTR gene, the most common mutation in CF patients, on at least one allele. In the first quarter of 2009, we initiated a Phase 2a clinical trial primarily designed to evaluate the safety and tolerability of multiple doses of VX-809 in approximately 90 patients with CF homozygous for the F508del mutation in the CFTR gene. In addition to assessing safety, this Phase 2a trial will evaluate the effect of VX-809 on biomarkers of CFTR function and whether VX-809 has an effect on FEV1. Enrollment in the trial is complete, and we expect to obtain data from this clinical trial in early 2010.

We have initiated a drug-drug interaction clinical trial of VX-809 and VX-770. Based on in vitro data, we believe that there is a rationale to explore the clinical potential for combining VX-809 and VX-770 and may seek to commence a combination clinical trial in patients with CF in the second half of 2010.

VX-509 is a novel oral JAK3 inhibitor that we believe has the potential to be used in multiple immune-mediated inflammatory disease, or IMID, indications. We have completed the Phase 1 clinical trials of VX-509, including a Phase 1 single and multiple, 14-day, dose-ranging clinical trial of VX-509 in healthy volunteers. We expect to initiate a Phase 2a clinical trial of VX-509 in patients with moderate to severe rheumatoid arthritis in the first quarter of 2010. This double-blind, randomized, placebo-controlled 12-week trial is expected to enroll approximately 200 patients, and we expect that initial clinical data from this trial, including measurements of safety, tolerability and clinical activity, will be available in the second half of 2010. We plan to continue to pursue collaborative opportunities for VX-509 with major pharmaceutical companies, but expect that no collaboration would be entered into until after the receipt of clinical data from the Phase 2a trial.

Corporate Collaborations

Corporate collaborations have been and will continue to be an important component of our business strategy. Under our agreement with Janssen, we have retained exclusive commercial rights to telaprevir in North America, and we are leading the global clinical development program. Janssen agreed to be responsible for 50% of the drug development costs under the development program for telaprevir in North America and the Janssen territories, to pay us contingent milestone payments based on successful development, approval and launch of telaprevir, to be responsible for the commercialization of telaprevir outside of North America and the Far East and to pay us royalties on any sales of telaprevir in its territories. The principal remaining milestones under our agreement with Janssen relate to marketing authorization for telaprevir from the European Medicines Evaluation Agency and the launch of telaprevir in the European Union. These milestones include $100.0 million related to regulatory submission and approval and $150.0 million related to launch of telaprevir. As a result of financial transactions discussed below that we entered into on September 30, 2009, the first $155.0 million of these milestone payments will . . .