Acceleron Pharma : Research & Development Day 2021

R E S E A R C H & D E V E L O P M E N T D A Y 2 0 2 1 J U N E 2 2 , 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 the Company's 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 Company's future cash position, and the potential of REBLOZYL® (luspatercept-aamt)as a therapeutic drug. 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-lookingstatements, 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 or accelerate faster than currently expected, that the Company or its collaboration partner, Bristol Myers Squibb ("BMS"), may be unable to successfully complete the clinical development of the Company's compounds, that the Company or BMS may be delayed in initiating, enrolling or completing any clinical trials, and that the Company's compounds may not receive regulatory approval or become commercially successful products. 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.

Welcome and R&D Day Agenda

8:00 - 8:25 AM

8:25 - 10:00 AM

10:00 - 10:35 AM

10:35 - 11:00 AM

ACCELERON VISION & S TRATEGY

Our Approach to Research & Development

WHO GROUP 1 & 2 PULMON ARY HYPER TENSION

Pulmonary Hypertension Q&A Session

S YS TEMIC SCLEROSIS - ASSOCIATED

INTERS TITIAL LUNG DISEASE

CLOSING REMARKS AND Q&A SESSION

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

H ABIB DABLE,

PR ESIDENT & C EO

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

OUR MISSION

is to transform the lives of patients with serious and rare diseases

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