Alnylam Initiates Phase II Clinical Trial to Evaluate Safety and Anti-viral Efficacy of ALN-RSV01 in the Treatment of Respiratory Syncytial Virus (RSV) Infection.

New Study Represents an Important Advancement in the Development of a Novel RNAi Therapeutic to Treat Viral Disease

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, today announced that it has initiated a Phase II experimental infection trial with ALN-RSV01 for the treatment of respiratory syncytial virus (RSV) infection. This trial is designed to evaluate the safety, tolerability, and anti-viral activity of ALN-RSV01 in adult subjects experimentally infected with RSV. ALN-RSV01 is the industry's most advanced RNAi therapeutic program for the treatment of an infectious disease and is an Alnylam proprietary program.

This new Phase II study represents an important component of Alnylam's clinical development plan for ALN-RSV01. At the 2007 Pediatric Academic Societies meeting in May, the company demonstrated the establishment of a model for the safe and reliable RSV infection of the upper respiratory tract of adult volunteers. Results showed that a robust and quantifiable infection was observed in 72 percent of subjects. The current Phase II trial is a randomized, double-blind, placebo-controlled study designed to evaluate the safety, tolerability, and anti-viral activity of ALN-RSV01 administered to healthy adult volunteers experimentally inoculated with RSV. A total of approximately 90 subjects are expected to be enrolled in the trial which will evaluate the effects of ALN-RSV01 on the following parameters of RSV infection: incidence of infection; measures of viral load; and occurrence of clinical symptoms. In the study, ALN-RSV01 will be administered both before and after inoculation with RSV; drug, virus, and placebo will all be administered intranasally. Data from this trial are expected toward the end of the year.

"Initiation of this well-controlled Phase II trial represents an important milestone in our efforts to advance ALN-RSV01 as an anti-viral drug for the treatment of RSV infection in patients. Experimental infection models have been used to develop many anti-viral treatments including those for flu and the common cold, and we believe that such a model is a significant advancement for the development of novel anti-RSV therapies," said Akshay Vaishnaw, M.D., Ph.D., Vice President, Clinical Research of Alnylam. "This step in our clinical development plan for ALN-RSV01 is particularly exciting as it offers the opportunity to demonstrate human proof-of-concept with an RNAi therapeutic in a viral disease."

"Working with Alnylam has been very gratifying as we have rapidly advanced ALN-RSV01 from pre-clinical studies to this Phase II study. To go from proof-of-concept in a rodent model to the potential for proof-of-concept in humans in such a short time is an important step forward in the development of ALN-RSV01 for the treatment of RSV infection," said John P. DeVincenzo, M.D., Associate Professor of Pediatrics and Infectious Diseases at the University of Tennessee Health Science Center. "Most importantly, the initiation of this new clinical study has the potential to advance the development of ALN-RSV01 for both adult and pediatric patients suffering from RSV infection, a disease with urgent need for viable treatment options."

In clinical trials to date, ALN-RSV01 has been found to be safe and well tolerated when administered intranasally in relevant doses to human adult volunteers where it demonstrated a safety profile comparable to placebo. Alnylam is currently enrolling subjects in the U.S. in a Phase I inhalation safety study with data expected in the second half of this year.

About Respiratory Syncytial Virus (RSV)

RSV is a highly contagious virus that causes infections in both the upper and lower respiratory tract. RSV infects nearly every child at least once by the age of two years and is a leading cause of hospitalization due to respiratory infection in children and in people with compromised immune systems, and others. RSV infection typically results in cold-like symptoms but can lead to more serious respiratory illnesses such as croup, pneumonia, bronchiolitis, and in extreme cases, death. RSV infection in the pediatric population accounts for more than 125,000 hospitalizations per year in the U.S. In addition, RSV infection in infants has been linked to the development of childhood asthma. As a result, there is a significant need for novel therapeutics to treat patients who become infected with RSV.

About RNA Interference (RNAi)

RNA interference (or RNAi) is a naturally occurring mechanism within cells for selectively silencing and regulating specific genes. The discovery of RNAi has been widely acknowledged as a major breakthrough in biology, and the technology was recognized for its potential broad impact in medicine with the award of the 2006 Nobel Prize for Physiology or Medicine. Since many diseases are caused by the inappropriate activity of specific genes, the ability to silence genes selectively through RNAi has accelerated the understanding of these genes and their related pathways. Additionally, RNAi could provide a new way to treat a wide range of human diseases. RNAi is induced by small, double-stranded RNA molecules. One method to activate RNAi is with chemically synthesized small interfering RNAs, or siRNAs, which are double-stranded RNAs that are targeted to a specific disease-associated gene. The siRNA molecules are used by the natural RNAi machinery in cells to cause targeted gene silencing.

About Alnylam

Alnylam is a biopharmaceutical company developing novel therapeutics based on RNA interference, or RNAi. The company is applying its therapeutic expertise in RNAi to address significant medical needs, many of which cannot effectively be addressed with small molecules or antibodies, the current major classes of drugs. Alnylam is building a pipeline of RNAi therapeutics; its lead program is in Phase II human clinical trials for the treatment of respiratory syncytial virus (RSV) infection. RSV infects nearly every child at least once by the age of two and accounts for more than 125,000 hospitalizations annually in the U.S. pediatric population. RSV infection also poses a great risk to the elderly and other adults with compromised immune systems. The company's leadership position in fundamental patents, technology, and know-how relating to RNAi has enabled it to form major alliances with leading companies including Merck, Medtronic, Novartis, and Biogen Idec. The company, founded in 2002, maintains global headquarters in Cambridge, Massachusetts, and has an additional operating unit in Kulmbach, Germany. For more information, visit www.alnylam.com.

Alnylam Forward-Looking Statements

Various statements in this release concerning our future expectations, plans, and prospects, including without limitation, statements concerning the use of RNAi therapeutics for the treatment of RSV and other viral disease and the availability of results of clinical trials and studies, constitute forward-looking statements for the purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by these forward-looking statements as a result of various important factors, including risks related to: our approach to discover and develop novel drugs, which is unproven and may never lead to marketable products; our ability to fund and the results of further pre-clinical and clinical trials; obtaining, maintaining and protecting intellectual property utilized by our products; our ability to enforce our patents against infringers and to defend our patent portfolio against challenges from third parties; our ability to obtain additional funding to support our business activities; our dependence on third parties for development, manufacture, marketing, sales, and distribution of products; the successful development of our product candidates, all of which are in early stages of development; obtaining regulatory approval for products; competition from others using technology similar to ours and others developing products for similar uses; our dependence on collaborators; and our short operating history; as well as those risks more fully discussed in the "Risk Factors" section of our most recent report on Form 10-Q on file with the Securities and Exchange Commission. In addition, any forward-looking statements represent our views only as of today and should not be relied upon as representing our views as of any subsequent date. We do not assume any obligation to update any forward-looking statements.