Acceleron Pharma, Developing Drugs to Treat Musculoskeletal and Metabolic Disorders, Secures $25 Million in Series A Funding

BOSTON, MA - February 13, 2004 - Acceleron Pharma, a biopharmaceutical company developing drugs to treat musculoskeletal and metabolic disorders, announced today that it has raised $25 million in its first round of private equity financing. The company has an exceptional team and a set of proprietary approaches that will enable it to develop a deep pipeline of products by targeting a large and high potential family of growth and differentiation factors. Founding investor Polaris Venture Partners led the series A round, with Advanced Technology Ventures, Flagship Ventures and Venrock Associates co-leading, and Sutter Hill Ventures joining.

"As a founder of Genetics Institute and an active member of the board of directors for more than fifteen years, I believe that the Acceleron discovery platform represents an exceptionally rich source of drug candidates," said Tom Maniatis. "Our broad and proprietary discovery platform, our exclusive intellectual property, and our world-class internal science team inspired investor enthusiasm," said John Knopf, founding president of Acceleron and previously vice president at Genetics Institute.

"Acceleron has an extraordinarily promising drug development program underway to address major unmet medical needs," said Christoph Westphal, general partner of Polaris and founding CEO of Acceleron. "We expect Acceleron to rapidly advance several product candidates through preclinical development."

Acceleron Pharma, based in Cambridge, MA, was founded in 2003 by John Knopf, Jasbir Seehra, Christoph Westphal, Tom Maniatis, Mark Ptashne, Wylie Vale, and founding scientific advisor Joan Massague. The founding team includes recognized leaders in academia and drug development. The academic founders are all members of the National Academy of Sciences, and several are members of the Institute of Medicine. Several founders also played key roles in the development of such notable biopharmaceutical successes as Genetics Institute and Neurocrine Biosciences.

The members of the Acceleron board of directors include Mike Carusi of Advanced Technology Ventures, Tony Evnin of Venrock Associates, Ed Kania of Flagship Ventures, John Knopf, Tom Maniatis, Wylie Vale, and Christoph Westphal. Pat Gage, a highly respected pharmaceutical executive and a Venture Partner at Flagship Ventures, will serve as Chairman.

About Acceleron Pharma

Acceleron is a biopharmaceutical company developing drugs for important unmet medical needs through proprietary approaches that exploit the therapeutic potential of a large family of growth and differentiation factors. Drug candidates will include both novel agonists and antagonists. The company was founded in 2003 and builds upon important ongoing research in the laboratories of its academic founders and consultants.

About Polaris Venture Partners

With over $2 billion under management, Polaris Venture Partners is a partnership of experienced venture capital investors and technology executives who help entrepreneurs build market-leading companies in information technology and life sciences. Polaris-backed companies include: Advanced Inhalation Research (AIR™); Akamai Technologies, Inc. (NASDAQ: AKAM); Allaire Corporation; Aspect Medical Systems (NASDAQ: ASPM); Centra Software (NASDAQ: CTRA); deCODE genetics (NASDAQ: DCGN); and SolidWorks (sold to Dassault SystŽmes). The company has offices in Boston and Seattle. More information about Polaris Venture Partners is available at (www.polarisventures.com).

About Advanced Technology Ventures

Founded in 1979, Advanced Technology Ventures (ATV) is a bi-coastal venture capital firm with more than $1.5 billion in capital under management. ATV works closely with entrepreneurial teams across several markets, including communications, IT infrastructure, software and services, and healthcare, to build emerging-growth business ventures into market leaders. For more information, visit (www.atvcapital.com).

About Flagship Ventures

Flagship Ventures is an early-stage venture capital firm focused on creating, financing, and building companies in the life science and information technology sectors. Flagship's team of twenty professionals is among the most experienced in the industry and represents a balance of venture capital, corporate executive, and entrepreneurship expertise. Its principals were involved as founders and investors in nearly 100 firms including: Alta Vista, Anesta, Antigenics, Aspect Medical Systems, Astral Point Communications, Celera Genomics, Cytyc, DataSage, Exact Sciences, PerSeptive Biosystems, and Telecorp PCS. Headquartered in Cambridge, MA, Flagship Ventures was founded in 1999 and manages over $600 million. For more information, visit (www.flagshipventures.com).

About Sutter Hill Ventures

Founded in 1964, Sutter Hill Ventures is one of Silicon Valley's original venture capital firms. Healthcare companies backed by Sutter Hill include Amylin, Cor Therapeutics, Molecular Devices, Neurex, Omnicell and Praecis. For more information, visit (www.shv.com).

About Venrock Associates

Venrock Associates was founded as the venture capital arm of the Rockefeller Family and continues a tradition of funding entrepreneurs that now spans over seven decades. With over 300 investments, the firm has an established a track record of identifying and supporting promising early stage, technology-based enterprises. Venrock maintains a tradition of collaboration with talented entrepreneurs to establish successful, enduring companies. Venrock's investments have included Intel, Apple Computer, CheckPoint Software, Genetics Institute, Idec Pharmaceuticals, Millennium Pharmaceuticals, and Illumina. For more information, please visit the Web site at (www.venrock.com).