Alnylam and Stanford University Scientists Discover New Role for microRNAs (miRNAs) in T Cell Biology and Immunity.

- Findings Published in the Journal Cell Show that miR-181a Regulates T Cell Responses to Antigens -

CAMBRIDGE, Mass. -- Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today publication of a study in the journal Cell by Alnylam and Stanford University scientists on the role of miRNAs in immunity. In the pre-clinical study, a specific miRNA, miR-181a, was shown to play an important role in controlling T cell responsiveness to antigens by regulating the T cell receptor signaling pathway. Because the T cell response to antigens is one of the primary components of certain autoimmune disorders, these findings further validate miRNAs as disease targets and point to new potential therapeutic applications for antagomirs, a novel class of oligonucleotide-based inhibitors of specific miRNAs.

"Our research points to a critical role for miRNAs, specifically miR-181a, in the regulation of T cell biology," said Dr. Mark Davis from Stanford University School of Medicine, a senior author of the publication. "We're excited about this new discovery as it represents the first clear example of a role for miRNAs in the immune response to antigens."

"In our study, upward or downward modulation of miR-181a was found to control certain aspects of T cell development and to regulate T cell responses to antigens via the T cell receptor signaling pathway," said Dr. Chang-Zheng Chen, also from Stanford University School of Medicine and a senior author of the publication.

"Alnylam's research on miRNAs derives from our discovery of antagomirs, a novel class of oligonucleotide inhibitors of miRNAs. These reagents have become powerful tools to investigate the role of miRNAs in biology and disease processes. We are fortunate to collaborate with some of the leading labs across the world, such as our colleagues at Stanford, in our efforts to explore therapeutic opportunities for miRNA antagonists," said Dr. Muthiah Manoharan, Vice President, Drug Discovery at Alnylam. "Moreover, this new paper in Cell continues Alnylam's commitment to scientific excellence and our broad leadership in RNAi research and its translation toward therapeutics."

T cells play a central and coordinating role in cell-mediated and acquired immunity. Recognition of both "self" and foreign molecules by T cells occurs through activation of a cell surface receptor called the T cell receptor. Activation of T cells through the T cell receptor involves the complex regulation of multiple biological pathways inside the cell. miRNAs are a broad class of small RNAs that have been shown to regulate the expression of a large number of genes in the human genome through the RNAi pathway, and many of these miRNAs are believed to be involved in disease processes. Certain miRNAs, including miR-181a, are known to play a role in B and T cell development, but their function in antigen recognition is poorly understood. Recently, Alnylam scientists and collaborators have discovered a new class of oligonucleotide therapeutics, called antagomirs, that inhibit the function of specific miRNAs in vitro and in vivo (Krutzfeldt et al. (2005) Nature 438, 685-689; Esau et al. (2006) Cell Metab., 3, 87-98).

In the current study, increasing expression of miR-181a was found to increase T cell sensitivity to antigens, while inhibiting miR-181a was found to decrease the immune response. miR-181a was found to regulate the responsiveness of the T cell receptor to antigens by the coordinated down-regulation of a set of phosphatase genes. Inhibiting miR-181a function with a selective antagomir, antagomir-181a, resulted in efficient reduction in T cell receptor sensitivity to antigens. Since abnormal T cell activity toward "self" antigens underscores the pathology in many autoimmune disorders, antagomirs selective for miR-181a could define a future therapeutic strategy for the treatment of these diseases.

About RNA Interference (RNAi)

RNA interference, or RNAi, is a naturally occurring mechanism within cells for selectively silencing and regulating specific genes. The discovery of RNAi has been widely acknowledged as a major breakthrough in biology, and the technology was recognized for its potential broad impact in medicine with the award of the 2006 Nobel Prize for Physiology or Medicine. 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 targeted gene silencing.

About microRNA (miRNA)

RNAi can also be induced by microRNAs, or miRNAs, that occur naturally within all mammalian cells. The miRNA molecules are encoded by the cell's own genes, giving rise to small RNA molecules that are similar in structure to siRNAs. There are believed to be over 250 confirmed miRNA genes in the human genome and there are many other predicted miRNAs. miRNAs are thought to work through RNAi to regulate the activity of an estimated one-third of genes in the genome. The inappropriate absence or presence of specific miRNA molecules in various cells has been shown to be associated with specific human diseases, including cancer and viral infections.

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. RSV infects nearly every child at least once by the age of two and accounts for more than 100,000 hospitalizations annually in the U.S. pediatric population. RSV infection also poses a great risk to the elderly and other adults with compromised immune systems. 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. For more information, visit www.alnylam.com.

Alnylam Forward-Looking Statements

Various statements in this release concerning our future expectations, plans and prospects, including without limitation statements related to the potential for miR-181a and other microRNAs, 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: Alnylam's approach to discover and develop novel drugs, which is unproven and may never lead to marketable products; Alnylam's ability to fund and the results of further pre-clinical and clinical trials; obtaining, maintaining and protecting intellectual property utilized by Alnylam's products; Alnylam's ability to enforce its patents against infringers and to defend its patent portfolio against challenges from third parties; Alnylam's ability to obtain additional funding to support its business activities; Alnylam's dependence on third parties for development, manufacture, marketing, sales, and distribution of products; the successful development of Alnylam's product candidates, all of which are in early stages of development; obtaining regulatory approval for products; competition from others using technology similar to Alnylam's and others developing products for similar uses; Alnylam's dependence on collaborators; and its short operating history; as well as those risks more fully discussed in the "Risk Factors" section of Alnylam's most recent report on Form 10-K 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.