Alnylam Receives Clearance from FDA to Initiate Phase I Study with ALN-VSP for the Treatment of Liver Cancers.

ALN-VSP Represents Industry's First Dual Targeting RNAi Therapeutic to Advance to Clinical Studies

Company on Track to Begin Dosing Patients in the First Half of 2009

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today that its investigational new drug (IND) application for ALN-VSP has been cleared by the U.S. Food and Drug Administration (FDA) to begin enrolling patients. ALN-VSP, an RNAi therapeutic for the treatment of liver cancers including hepatocellular carcinoma and other solid tumors with liver involvement, contains two small interfering RNAs (siRNAs, the molecules that mediate RNAi), formulated in a lipid nanoparticle developed by Tekmira Pharmaceuticals Corporation. ALN-VSP is designed to target two genes critical in the growth and development of cancer: kinesin spindle protein, or KSP, required for tumor proliferation; and vascular endothelial growth factor, or VEGF, required for tumor growth. Pre-clinical data in mouse tumor model studies have demonstrated robust efficacy of ALN-VSP, including suppression of targeted genes, demonstration of an RNAi mechanism of action, tumor reduction, and extension of survival.

"ALN-VSP represents Alnylam's first IND for a systemically delivered RNAi therapeutic, which is a testament to the very strong progress we have made in achieving delivery of siRNAs," said Akshay Vaishnaw, M.D., Ph.D., Senior Vice President, Clinical Research at Alnylam. "We are very excited about reaching yet another important milestone in this program and in our overall efforts. As planned, we expect to initiate patient dosing in the first half of this year, which positions us solidly on track to meet our goal of having three programs in clinical trials in 2009."

The proposed Phase I study is a multi-center, open label, dose escalation trial to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of intravenous ALN-VSP in patients with advanced solid tumors with liver involvement. Additional study design details will be provided upon initiation of the clinical study.

About RNA Interference (RNAi)

RNAi (RNA interference) is a revolution in biology, representing a breakthrough in understanding how genes are turned on and off in cells, and a completely new approach to drug discovery and development. Its discovery has been heralded as "a major scientific breakthrough that happens once every decade or so," and represents one of the most promising and rapidly advancing frontiers in biology and drug discovery today which was awarded the 2006 Nobel Prize for Physiology or Medicine. RNAi is a natural process of gene silencing that occurs in organisms ranging from plants to mammals. By harnessing the natural biological process of RNAi occurring in our cells, the creation of a major new class of medicines, known as RNAi therapeutics, is on the horizon. RNAi therapeutics target the cause of diseases by potently silencing specific messenger RNAs (mRNAs), thereby preventing disease-causing proteins from being made. RNAi therapeutics have the potential to treat disease and help patients in a fundamentally new way.

About Alnylam Pharmaceuticals

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 leading the translation of RNAi as a new class of innovative medicines with peer-reviewed research efforts published in the world's top scientific journals including Nature, Nature Medicine, and Cell. The company is leveraging these capabilities to build a broad pipeline of RNAi therapeutics; its most advanced program is in Phase II human clinical trials for the treatment of respiratory syncytial virus (RSV) infection and is partnered with Cubist and Kyowa Hakko. In addition, the company is developing RNAi therapeutics for the treatment of a wide range of disease areas, including liver cancers, hypercholesterolemia, Huntington's disease, and TTR amyloidosis. 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 Medtronic, Novartis, Biogen Idec, Roche, Takeda, Kyowa Hakko, and Cubist. To reflect its outlook for key scientific, clinical, and business initiatives, Alnylam established "RNAi 2010" in January 2008 which includes the company's plan to significantly expand the scope of delivery solutions for RNAi therapeutics, have four or more programs in clinical development, and to form four or more new major business collaborations, all by the end of 2010. Alnylam is a joint owner of Regulus Therapeutics, a joint venture focused on the discovery, development, and commercialization of microRNA therapeutics. Founded in 2002, Alnylam maintains headquarters in Cambridge, Massachusetts. For more information, please visit http://www.alnylam.com.

Alnylam Forward-Looking Statement

Various statements in this release concerning Alnylam's future expectations, plans and prospects, 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 the company's ability to successfully research and develop products, such as ALN-VSP for the treatment of liver cancers, including the possibility that ALN-VSP will not be demonstrated to be safe and effective when tested in humans, as well as those risks more fully discussed in the "Risk Factors" section of its most recent quarterly report on Form 10-Q on file with the Securities and Exchange Commission. In addition, any forward-looking statements represent Alnylam's views only as of today and should not be relied upon as representing its views as of any subsequent date. Alnylam does not assume any obligation to update any forward-looking statements.