Acceleron Pharma : ATS 2021 International Conference

A T S 2 0 2 1 I N T E R N A T I O N A L C O N F E R E N C E

A C C E L E R O N I N V E S T O R A N D A N A L Y S T C A L L M A Y 1 9 , 2 0 2 1

Acceleron Forward-Looking Statements

THIS PRESENTATION CONTAINS FORWARD-LOOKING STATEMENTS ABOUT THE COMPANY'S STRATEGY, FUTURE PLANS AND PROSPECTS, including statements regarding the development and commercialization of sotatercept in pulmonary arterial hypertension ("PAH") and of the Company's other compounds, the timeline for clinical development and regulatory approval of the Company's compounds and the expected timing for reporting of data from ongoing clinical trials. The words "anticipate," "believe," "could," "estimate," "expect," "goal," "intend," "may," "plan," "potential," "project," "should," "target," "will," "would," and similar expressions are intended to identify forward- looking statements, although not all forward-lookingstatements contain these identifying words.

ACTUAL RESULTS COULD DIFFER MATERIALLY FROM THOSE INCLUDED IN THE FORWARD-LOOKING STATEMENTS DUE TO VARIOUS factors, risks and uncertainties, including, but not limited to, that preclinical testing of the Company's compounds and data from clinical trials may not be predictive of the results or success of ongoing or later clinical trials, that regulatory approval of the Company's compounds in one indication or country may not be predictive of approval in another indication or country, that the development of the Company's compounds may take longer and/or cost more than planned, that the Company may be unable to successfully complete the clinical development of the Company's compounds, that the Company may be delayed in initiating, enrolling or completing any clinical trials, that the Company's compounds may not receive regulatory approval or become commercially successful products, and that Breakthrough Therapy or Priority Medicines (PRIME) designation may not expedite the development or review of sotatercept. These and other risks and uncertainties are identified under the heading "Risk Factors" included in the Company's most recent Annual Report on Form 10-Kand other filings that the Company has made and may make with the SEC in the future.

THE FORWARD-LOOKING STATEMENTS CONTAINED IN THIS PRESENTATION ARE BASED ON MANAGEMENT'S CURRENT VIEWS, PLANS, estimates, assumptions and projections with respect to future events, and the Company does not undertake and specifically disclaims any obligation to update any forward-lookingstatements.

2	This presentation is for investor relations purposes only -
	Not for product promotional purposes.

H ABIB DABLE

C H IEFH AEXECB I B D UA BTIVL E E OF F IC ER

C H I E F E X E C U T I V E O F F I C E R

3	This presentation is for investor relations purposes only -
	Not for product promotional purposes.

Our Vision for Sotatercept in Pulmonary Arterial Hypertension (PAH)

BACKBONE

THERAPY

IN PAH

4	Sotatercept is an investigational therapy that is not approved for any use in any country.

This presentation is for investor relations purposes only - Not for product promotional purposes.

J AY BAC K S TROM , M D, M PH

H E A D HOAFBRI BE SD EA BALREC H &

C H I E F E X E C U T I V E O F F I C E R

D E V E L O P M E N T

5	This presentation is for investor relations purposes only -
	Not for product promotional purposes.