Alnylam Initiates Phase I Clinical Study of Inhaled Formulation of ALN-RSV01, an RNAi Therapeutic for the Treatment of Respiratory Syncytial Virus (RSV) Infection.

- Continued Progress in Clinical Development of the Industry's Most Advanced RNAi Therapeutic for the Treatment of an Infectious Disease -

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today that it has initiated a Phase I human clinical trial of an inhaled formulation of ALN-RSV01 in the U.S. to evaluate its safety, tolerability, and pharmacokinetics in healthy adult volunteers. The inhaled formulation of ALN-RSV01 used in this Phase I study is a nebulized formulation, and advances previous clinical work for ALN-RSV01 administered as an intranasal spray. ALN-RSV01, an un-partnered Alnylam program, is an RNAi therapeutic in clinical development for the treatment of respiratory syncytial virus (RSV) infection.

"There is a significant need for novel therapeutics to effectively treat patients with RSV infection, the leading cause of pediatric hospitalization in the U.S. today and a prevalent infection in immune-compromised adult populations," said John P. DeVincenzo, M.D., Associate Professor of Pediatrics at the University of Tennessee Health Science Center. "Based on its novel mechanism of action, safety in humans to date, and encouraging pre-clinical efficacy data, I am hopeful that ALN-RSV01 has the potential to impact this important medical issue."

Alnylam previously completed two Phase I human clinical trials of ALN-RSV01 using an intranasal formulation. The previous studies demonstrated that ALN-RSV01 was safe and well tolerated when administered intranasally in relevant doses to human volunteers and had a profile comparable to placebo. This newly initiated Phase I trial with inhaled ALN-RSV01 uses a formulation that is designed to deliver the RNAi therapeutic to the lungs, and is the expected formulation for the treatment of RSV in naturally infected patients. Models of this aerosolized formulation of ALN-RSV01 predict that it can be delivered to the alveoli and the small airways of the infant and adult human lung.

"Initiation of this clinical trial represents an important milestone in Alnylam's efforts to advance ALN-RSV01 as a novel anti-viral RNAi therapeutic for the treatment of RSV infection. We expect results from this newly initiated clinical trial, combined with previously completed Phase I studies, will provide us with safety data from approximately 180 human subjects in placebo-controlled studies, representing one of the most extensive clinical experiences with an RNAi therapeutic," said Akshay Vaishnaw, M.D., Ph.D., Vice President, Clinical Research of Alnylam. "We believe that ALN-RSV01 could be a promising treatment option for patients infected with RSV, and as an un-partnered clinical program, it represents an important component of Alnylam's balanced pipeline of proprietary and partnered RNAi therapeutics programs."

Later this year, the company expects to initiate an experimental infection, or "viral challenge," study with the intranasal formulation of ALN-RSV01 in healthy adult volunteers.

Inhalation Phase I Trial Details

Alnylam will be conducting a two-part Phase I randomized, double-blind, placebo-controlled trial in healthy adult volunteers to assess the safety, tolerability, and pharmacokinetics of aerosolized ALN-RSV01 when administrated by inhalation via nebulizer, which is a machine that converts liquid medication into a fine mist that is inhaled through a mouthpiece or mask. It is anticipated that a total of 80 healthy adults will be enrolled into one of eight cohorts. Single ascending doses of aerosolized ALN-RSV01 or placebo will be administered by inhalation to four cohorts of eight subjects each with five subjects receiving ALN-RSV01 and three subjects receiving placebo in each cohort for a total of 32 subjects. Subsequently, multiple ascending doses of aerosolized ALN-RSV01 or placebo will be administered once daily by inhalation for three consecutive days to four cohorts of 12 subjects each with eight subjects receiving ALN-RSV01 and four subjects receiving placebo in each cohort for a total of 48 subjects. Data from this trial are expected in the first half of 2007.

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 major 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 100,000 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. Since many diseases are caused by the inappropriate activity of specific genes, the ability to silence genes selectively through 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 highly 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 I human clinical trials for the treatment of respiratory syncytial virus (RSV) infection, which is the leading cause of hospitalization in infants in the U.S. 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. Alnylam is honored to be the "emerging/mid-cap" company recipient of the 2006 James D. Watson Helix Award, the biotechnology industry's award for outstanding achievement. For more information, visit www.alnylam.com.

Alnylam Forward-Looking Statements

Various statements in this release concerning our future expectations, plans, and prospects, including our plans with respect to the initiation and completion of clinical trials of ALN-RSV01, the need for novel RSV therapeutics, the expected formulation for an RSV therapeutic, and our views with respect to the potential for RNAi therapeutics, including ALN-RSV01, 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; 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. Alnylam does not assume any obligation to update any forward-looking statements.