Alnylam and Collaborators at Harvard Medical School Demonstrate In Vivo Silencing of Key Genes Implicated in the Transmission of Herpes Simplex Virus-2 (HSV-2).

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today the publication of new data in the journal Cell Host & Microbe demonstrating that topical administration of an RNAi therapeutic resulted in robust and durable protection from the transmission of the herpes simplex virus-2 (HSV-2) in mice. The work is the result of an ongoing collaboration between Alnylam and the lab of Judy Lieberman, M.D., Ph.D., Senior Investigator of the Immune Disease Institute and Professor of Pediatrics, Harvard Medical School, and is supported in part by a grant from the National Institutes of Health (AI070302).

"HSV infection causes significant morbidity and is also an important cofactor for HIV-1 transmission," said Dr. Lieberman. "A topical microbicide with the ability to protect against HSV-2 could contribute significantly to controlling these widespread serious infections. We are encouraged by the results published today with Alnylam which suggest that an RNAi therapeutic approach could provide sustained protection against transmission of HSV-2."

The work described in the publication (Wu et al., Cell Host & Microbe 5, 84-94; 2009) used cholesterol-conjugated small interfering RNAs (siRNA, the molecules that mediate RNAi) targeting the HSV gene UL29 and the cell surface receptor nectin-1 which has been identified as an endogenous host receptor for HSV-2. Intravaginal delivery of siRNAs demonstrated durable protection from transmission of the virus. Specifically, in vivo data from this study showed that animals treated with siRNAs targeting UL29 and nectin-1 were protected from lethal HSV infection for about one week and showed a survival rate of up to 80%. Importantly, these results showed that cholesterol-conjugated siRNAs did not activate inflammation or interferon response genes.

"Our collaboration with Dr. Lieberman and her lab has been very productive and we are pleased to have the opportunity to work with a leading group of researchers in this area," said Muthiah (Mano) Manoharan, Ph.D., Vice President, Drug Discovery. "We are encouraged by these robust results, which point to the potential for a cholesterol conjugate approach for topical RNAi therapeutic applications, including mucosa and skin. We believe these data further demonstrate our continued progress on delivery of RNAi therapeutics, including the broad applications of cholesterol conjugation for effective delivery of RNAi therapeutics both by systemic and direct routes due to improved biodistribution and cellular uptake of this conjugate."

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 a treatment for the HSV-2, 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.