Alnylam Reports Positive Outcome in European Opposition Proceedings on Kreutzer-Limmer I Patent; Amended Claims Broadly Cover siRNAs with Key Features Critical for RNAi Therapeutics.

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today that the European Patent Office (EPO) has upheld key features of the company's Kreutzer-Limmer I patent (EP 1144623) with claims covering small interfering RNAs (siRNAs), the molecules that mediate RNAi. This patent was originally granted in Europe on August 28, 2002, but was opposed by several parties, a legal practice that is common for European patents. The amended patent claims cover certain structural requirements for siRNAs that are important for therapeutic activity.

"The outcome of the European opposition proceedings today is a positive step forward in Alnylam's strategic consolidation of intellectual property needed for advancement of RNAi therapeutics as products. Today's ruling adds strength to an intellectual property estate for RNAi therapeutics that contains well over 150 patents issued in major markets," said John Maraganore, Ph.D., President and Chief Executive Officer of Alnylam Pharmaceuticals. "In addition to this ruling, Alnylam's intellectual property position was greatly strengthened with the recent issuance by the United States Patent and Trademark Office of our exclusively held Tuschl II patent. Further, we expect issuance of new patents from the Tuschl II series within the next 6 months. Alnylam's intellectual property estate enables our efforts to build value through major partnerships, target-by-target therapeutic licenses in our InterfeRx program, and licenses to the reagent and services market, where we have an unmatched track record of execution."

The Kreutzer-Limmer I patent that is the subject of the EPO's ruling (EP 1144623) is one of many components of Alnylam's intellectual property (IP) estate, which in aggregate, broadly covers the "fundamental," chemistry, and target IP necessary for the development and commercialization of RNAi therapeutics. As originally granted, the claims of this patent covered siRNAs with up to 25 nucleotides complementary to a target gene, and were obtained by use during prosecution of a so-called "Disclaimer Practice" that was deemed to be not applicable as a result of a separate ruling issued by the Enlarged Board of the EPO. In consequence, the claims were amended to cover siRNAs with a shorter length and other required features. Specifically, the claims in the upheld patent cover methods, medicaments, and uses of siRNAs with:

--a region of complementarity to a target gene between 15 and 21 nucleotides in length;

--an overall length of between 15 and 21 base pairs; and,

--a double-stranded structure that is stabilized by a chemical linkage of the single strands, such as and including standard modifications used for stabilization.

"We're gratified that the EPO has recognized the inventive contributions of Drs. Kreutzer and Limmer to the field of RNAi therapeutics," said Robert Millman, Chief Intellectual Property Counsel of Alnylam Pharmaceuticals. "The amended claims granted through the oral opposition proceedings cover features of siRNAs that are critical for RNAi therapeutics. Importantly, the patent covers methods, medicaments, and uses of siRNAs in Europe, the world's second largest pharmaceutical market."

Alnylam's IP estate includes issued or granted fundamental patents and patent applications that claim the broad structural and functional properties of synthetic RNAi therapeutic products. These include: the recently issued Tuschl II patent, U.S. Patent No. 7,056,704, which broadly covers methods of making siRNAs to silence any and all disease targets; a separate Tuschl II series patent application, U.S. 10/832,248, for which claims were recently allowed that broadly cover methods of making siRNAs with or without chemical modifications; and other pending applications from the Tuschl II series. In addition to the Kreutzer-Limmer I patent that was the subject of today's ruling (EP 1144623), Alnylam's IP estate includes other Kreutzer-Limmer I and II patents acquired through the July 2003 merger with Ribopharma AG (now Alnylam Europe AG): EP 1214945, covering compositions, methods, and uses of siRNAs with a length between 15 and 49 nucleotides; and EP 1352061, covering therapeutic compositions, methods, and uses of siRNA and derivatives directed toward over 125 disease targets. Additional fundamental patents and patent applications licensed to Alnylam on an exclusive or non-exclusive basis include those of Crooke (U.S. Patent Nos. 5,898,031 and 6,107,094), Fire and Mello (U.S. Patent No. 6,506,559), Glover et al. (EP 1230375), and Tuschl et al. (Tuschl I, patent pending), among others. In addition, Alnylam has a broad worldwide license for RNAi therapeutics from Isis Pharmaceuticals, Inc. for more than 150 issued patents pertaining to the chemical modification of oligonucleotides used to introduce "drug-like" properties in siRNAs. These include key issued patents for chemical stabilization of siRNAs such as phosphorothioate and 2'-O-methyl modifications (Buhr, U.S. Patent No. 6,473,205) and 2'-fluoro modifications (Cook, U.S. Patent Nos. 5,670,633; 6,005,087; and 6,531,584) of oligonucleotides.

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 1 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, and Novartis. 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 views with respect to the timing and the future issuance of patents and the importance and scope of our intellectual property rights, 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. We do not assume any obligation to update any forward-looking statements.