Acceleron Pharma, Inc. (NASDAQ:XLRN) today announced the closing of its initial public offering of 6,417,000 shares of common stock, including 837,000 shares of common stock issued upon the exercise in full by the underwriters of their option to purchase additional shares to cover over-allotments, at a public offering price of $15.00 per share, before underwriting discounts. Separately, in a concurrent, side-by-side private placement, Acceleron’s collaboration partner, Celgene Corporation (NASDAQ:CELG), purchased 666,667 shares of common stock from Acceleron at the public offering price. Including the private placement to Celgene, the aggregate net proceeds to the Company, after underwriting discounts and commissions and other estimated offering expenses, were approximately $96.7 million. Citigroup and Leerink Swann acted as joint book-running managers for the offering. Piper Jaffray & Co. acted as lead manager and JMP Securities LLC acted as co-manager for the offering. A registration statement relating to these securities was declared effective on September 18, 2013. Copies of the final prospectus relating to the offering may be obtained from Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY, 11717, or by email at email@example.com, or by phone at 800-831-9146; or Leerink Swann, Attention: Syndicate Department, One Federal Street, 37 th Floor, Boston, MA, 02110, or by email at Syndicate@Leerink.com, or by phone at 800-808-7525. This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of, these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of such state or jurisdiction. About Acceleron Acceleron is a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of novel protein therapeutics for cancer and rare diseases. The company is a leader in understanding the biology of the Transforming Growth Factor-Beta (TGF-β) protein superfamily, a large and diverse group of molecules that are key regulators in the growth and repair of tissues throughout the human body, and in targeting these pathways to develop important new medicines. Acceleron has built a highly productive R&D platform that has generated innovative clinical and preclinical protein therapeutic candidates with novel mechanisms of action. These protein therapeutic candidates have the potential to significantly improve clinical outcomes for patients with cancer and rare diseases.