Alnylam Reports Phase I Clinical Safety Data for ALN-RSV01, an RNAi Therapeutic for the Treatment of RSV Infection; Results Reported at the 2006 Pediatric Academic Societies' Annual Meeting

"These Phase I study results are an important step forward forAlnylam and for the entire field of RNAi therapeutics. Data from thesetrials provide us with a significant clinical experience for ALN-RSV01with 101 subjects enrolled in the two trials combined," said JohnMaraganore, Ph.D., President and Chief Executive Officer of Alnylam."Treatment of RSV infection, the leading cause of pediatrichospitalization in the U.S. today and a prevalent infection in certainadult populations, represents a major unmet medical need in a largenumber of patients. We believe that ALN-RSV01 is a promising treatmentoption for these patients and, as an unpartnered clinical program, animportant component of Alnylam's balanced pipeline of wholly owned andpartnered RNAi therapeutics."

"As a clinician committed to the advancement of new therapies forthe treatment of pediatric infectious diseases, I am very encouragedby the results of these first human studies with ALN-RSV01," said JohnP. DeVincenzo, M.D., Associate Professor of Pediatrics at theUniversity of Tennessee Health Science Center. "Based on these Phase Istudies, the encouraging pre-clinical data showing anti-viral activityat similar doses, and the drug's novel mechanism of action, ALN-RSV01may represent a breakthrough treatment option for patients infectedwith RSV."

Alnylam conducted two Phase I trials with ALN-RSV01 to evaluatethe safety, tolerability, and pharmacokinetics of ALN-RSV01 in healthyadult volunteers. Both trials were double-blind, placebo-controlled,and randomized. In total, 101 subjects were enrolled in the trials and65 were exposed to ALN-RSV01. The subjects received single or multipledaily doses of ALN-RSV01 or saline placebo in a nasal spray. Resultsshowed that ALN-RSV01 was safe when administered intranasally inrelevant doses to human volunteers, and comparable to placebo withrespect to any reported adverse events. All reported adverse eventsfor both ALN-RSV01 and placebo subjects were mild, with no reportedserious adverse events. Further, there was no evidence of laboratoryor electrocardiographic abnormalities in subjects exposed to drug.Finally, as expected, there was no significant systemic exposure ofALN-RSV01 when administered intranasally.

"These data are an important milestone as we advance ALN-RSV01into further clinical development. In the second half of this year weexpect to initiate a Phase I study with an inhaled formulation ofALN-RSV01, and we are also actively exploring the initiation of anexperimental infection, or 'viral challenge', study with ourintranasal formulation in adult volunteers later in the year. Webelieve that these and other efforts will enable us to initiate aPhase II trial in naturally infected RSV patients in the first half of2007," said Barry Greene, Chief Operating Officer of Alnylam."Finally, as the industry's most advanced RNAi therapeutic for thetreatment of infectious diseases, ALN-RSV01's development provides acritically important roadmap for our other pipeline efforts, includingthose with Novartis on pandemic influenza."

The data from the Phase I trials are being presented at the 2006Pediatric Academic Societies' (PAS) Annual Meeting being held in SanFrancisco, April 29 - May 2. Presentation of the results are takingplace in two sessions: the State of the Art Plenary Session #3810titled "RNA Interference, Technological Development of siRNAs andPotential Treatments for Childhood Diseases" to be held in MosconeWest, Room 3016-3018 on April 30, 2006 at 4:15 p.m. PT; and thePAS/PIDS platform session #4130 titled "Infectious Diseases II" on May1, 2006 at 8:00 a.m. PT in Moscone West, Room 3001.

Trial Details

The trial conducted in the U.S. enrolled 34 healthy adultvolunteers. Drug or placebo was administered intranasally in singleascending doses (1.5, 5, 15, 50, or 150 mg) across five cohorts. Thetrial conducted in Europe enrolled 67 healthy adult volunteers. Drugor placebo was administered intranasally in both single ascendingdoses (5, 25, or 150 mg) across three cohorts and in multipleascending doses (5, 25, and 150 mg) daily for five consecutive daysacross three cohorts. Dose levels administered were comparable toactive anti-viral dose levels observed in pre-clinical animal studies.In both studies, ALN-RSV01 was evaluated for safety, tolerability, andpharmacokinetics.

About Respiratory Syncytial Virus (RSV)

RSV is a highly contagious virus that causes infections in boththe upper and lower respiratory tract. RSV infects nearly every childat least once by the age of two years and is a major cause ofhospitalization due to respiratory infection in children and peoplewith compromised immune systems, and others. RSV infection typicallyresults in cold-like symptoms but can lead to more serious respiratoryillnesses such as croup, pneumonia, bronchiolitis, and in extremecases, death. RSV infection in the pediatric population accounts formore than 100,000 hospitalizations per year in the U.S. In addition,RSV infection in infants has been linked to the development ofchildhood asthma. As a result, there is a significant need for noveltherapeutics to treat patients who become infected with RSV.

About RNA Interference (RNAi)

RNA interference, or RNAi, is a naturally occurring mechanismwithin cells for selectively silencing and regulating specific genes.Since many diseases are caused by the inappropriate activity ofspecific genes, the ability to silence genes selectively through RNAicould provide a new way to treat a wide range of human diseases. RNAiis induced by small, double-stranded RNA molecules. RNAi can beactivated by chemically synthesized small interfering RNAs, or siRNAs,which are double-stranded RNAs that are targeted to a specificdisease-associated gene. The siRNA molecules are used by the naturalRNAi machinery in cells to cause highly targeted gene silencing.Alnylam's initial drug development programs are focused on DirectRNAi(TM) therapeutics which are siRNAs administered directly todiseased parts of the body. In parallel, the company is developingSystemic RNAi(TM) therapeutics that travel through the bloodstream toreach diseased parts of the body.

About Alnylam

Alnylam is a biopharmaceutical company developing noveltherapeutics based on RNA interference, or RNAi. The company isapplying its therapeutic expertise in RNAi to address significantmedical needs, many of which cannot effectively be addressed withsmall molecules or antibodies, the current major classes of drugs.Alnylam is building a pipeline of RNAi therapeutics; its lead programis in Phase I human clinical trials for the treatment of respiratorysyncytial virus (RSV) infection, which is the leading cause ofhospitalization in infants in the U.S. The company's leadershipposition in fundamental patents, technology, and know-how relating toRNAi has enabled it to form major alliances with leading companiesincluding Merck, Medtronic, and Novartis. The company, founded in2002, maintains global headquarters in Cambridge, Massachusetts, andhas an additional operating unit in Kulmbach, Germany. Alnylam ishonored to be the "emerging/mid-cap" company recipient of the 2006James D. Watson Helix Award, the biotechnology industry's award foroutstanding corporate achievement. For more information, please visitwww.alnylam.com.

Alnylam Forward-Looking Statements

Various statements in this release concerning our futureexpectations, plans, and prospects, including statements with respectto clinical development plans for ALN-RSV01 and the potential forALN-RSV01 to be a treatment option for RSV infection patients,constitute forward-looking statements for the purposes of the safeharbor provisions under The Private Securities Litigation Reform Actof 1995. Actual results may differ materially from those indicated bythese forward-looking statements as a result of various importantfactors, including risks related to: our approach to discover anddevelop novel drugs, which is unproven and may never lead tomarketable products; obtaining, maintaining and protectingintellectual property utilized by our products; our ability to enforceour patents against infringers and to defend our patent portfolioagainst challenges from third parties; our ability to obtainadditional funding to support our business activities; our dependenceon third parties for development, manufacture, marketing, sales anddistribution of our products; the successful development of products,all of which are in early stages of development; obtaining regulatoryapproval for products; competition from others using technologysimilar to ours and others developing products for similar uses; ourdependence on collaborators; and our short operating history; as wellas those risks more fully discussed in the "Risk Factors" section ofour most recent report on Form 10-K on file with the Securities andExchange Commission. In addition, any forward-looking statementsrepresent our views only as of today and should not be relied upon asrepresenting our views as of any subsequent date. We do not assume anyobligation to update any forward-looking statements.