PRESS RELEASE: Acceleron Pharma Completes $31M Series C Financing

Acceleron Pharma Completes $31M Series C Financing

Top venture syndicate invests to advance expanding pipeline of products that modulate tissue growth and repair

Cambridge, Mass. – October 30, 2007 - Acceleron Pharma, Inc., a biopharmaceutical company developing novel therapeutics that modulate the growth of tissues including bone and muscle, today announced it raised $31M in a Series C financing. Bessemer Venture Partners led the round along with other new investors MPM BioEquities and QVT Financial. All existing institutional investors participated in the round including Advanced Technology Ventures, Flagship Ventures, OrbiMed Advisors, Polaris Ventures, Sutter Hill Ventures and Venrock.

Acceleron plans to use the proceeds from this financing to advance its clinical and preclinical pipeline and further develop its product platform. In the first quarter of 2008, Acceleron expects to advance its ACE-011 program for bone growth into phase 2 clinical trials and to initiate a phase 1 study of its ACE-031 program for increasing muscle mass and strength. The company expects to bring its third drug candidate, ACE-041, into clinical trials in the second half of 2008.

“We are pleased that these leading investment firms recognize the value of Acceleron’s rich pipeline and unparalleled expertise in developing these novel therapies” said John Knopf, Ph.D., Chief Executive Officer of Acceleron. “The company has made enormous progress and this financing will enable us to continue to advance our lead programs through later-stage clinical studies.”

“Bessemer Venture Partners invests in biopharmaceutical companies pursuing high-potential novel drugs. Acceleron is creating an extremely promising pipeline of products led by the programs for bone and muscle growth,” said Christopher Gabrielli, senior partner at Bessemer Venture Partners. “We are delighted to invest in Acceleron and join an experienced and proven management team along with a very strong and committed group of investors.”

In connection with the financing, Acceleron has reorganized its expanding Board of Directors, which is comprised of Tony Evnin (Venrock), L. Patrick Gage, Ph.D. (PDL), Jean George (ATV), Carl Gordon, Ph.D. (OrbiMed), Ed Kania (Flagship), John Knopf, Ph.D. (Acceleron), Tom Maniatis, Ph.D. (Harvard), Terry McGuire (Polaris), Richard Pops (Alkermes), and Wylie Vale, Ph.D. (Salk). Richard Pops has been elected Lead Director.

“Acceleron‘s unique product platform has led to the internal generation of a robust pipeline of promising therapeutic candidates that modulate growth and repair of bone, muscle and other tissues. Clinical candidates are already in development and we expect at least one new product to progress into the clinic each year for the next several years,” commented Richard Pops, Chairman of Alkermes and Lead Director of Acceleron’s Board of Directors. “It has been a pleasure to work with the talented and productive team at Acceleron, and we all look forward to continued progress in exploiting the potential of these novel proteins.”

About Acceleron Pharma

Acceleron is a privately held biopharmaceutical company committed to discover, develop, manufacture and commercialize novel biotherapeutics that modulate the growth of bone, muscle, fat and the vasculature to treat musculoskeletal, metabolic and cancer-related diseases. Acceleron’s scientific approach takes advantage of its unique insight into the regenerative powers of two protein families: the Growth and Differentiation Factors (GDFs) and Bone Morphogenetic Proteins (BMPs). ACE-011, a novel bone forming agent, is the company’s lead program, and is being developed to reverse bone loss in diseases such as cancer-related bone loss. In addition, the company is advancing through preclinical development product candidates that increase muscle mass, control angiogenesis and inhibit fat accumulation. Acceleron utilizes proven biotherapeutic technologies and capitalizes on the company’s internal GMP manufacturing capability to rapidly and efficiently advance its therapeutic programs. The investors in Acceleron are Advanced Technology Ventures, Bessemer Ventures, Flagship Ventures, MPM BioEquities, OrbiMed Advisors, Polaris Ventures, QVT Financial, Sutter Hill Ventures and Venrock.

Contact: Steven Ertel, Vice President, Corporate Development, Acceleron Pharma, tel: 617-520-1334 and Paul Kidwell (Media) Suda Communications LLC, tel: 617-296-3854.