Acceleron Announces Pricing of Initial Public Offering

CAMBRIDGE, Mass.--(BUSINESS WIRE)--

Acceleron Pharma, Inc. today announced the pricing of its initial public offering of 5,580,000 shares of common stock at a public offering price of $15.00 per share, before underwriting discounts. In addition, Acceleron has granted the underwriters a 30-day option to purchase up to an additional 837,000 shares of common stock at the public offering price, less underwriting discounts. Separately, in a concurrent, side-by-side private placement, Acceleron's collaboration partner, Celgene Corporation CELG, has agreed to purchase 666,667 shares of common stock from Acceleron at the public offering price. Acceleron's common stock has been approved for listing on the NASDAQ Global Market and is expected to begin trading under the ticker symbol “XLRN” on September 19, 2013.

Citigroup and Leerink Swann are acting as joint book-running managers for the offering. Piper Jaffray & Co. is acting as lead manager and JMP Securities LLC is acting as co-manager for the offering.

A registration statement relating to these securities was declared effective on September 18, 2013. The offering will be made only by means of a prospectus, copies of which may be obtained from Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY, 11717, or by email at batprospectusdept@citi.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.