Exhibit 99.1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) promulgated under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing with the other Reporting Person (as such term is defined in the Schedule 13D referred to below) on behalf of each of them of a statement on Schedule 13D (including any and all amendments thereto) with respect to Common Stock, par value $0.001 per share, of Acceleron Pharma Inc., a Delaware corporation, and that this Agreement may be included as an Exhibit to such joint filing.

The undersigned further agree that each party hereto is responsible for the timely filing of such Statement on Schedule 13D and any amendments thereto, and for the accuracy and completeness of the information concerning such party contained therein, provided, however, that no party is responsible for the accuracy or completeness of the information concerning any other party, unless such party knows or has reason to believe that such information is inaccurate.

This Agreement may be executed in any number of counterparts, all of which together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned hereby execute this Agreement this 16th day of July, 2020.

BRISTOL-MYERS SQUIBB COMPANY
By:	/s/ Katherine R. Kelly
Name:	Katherine R. Kelly
Title:	Corporate Secretary
CELGENE CORPORATION
By:	/s/ Katherine R. Kelly
Name:	Katherine R. Kelly
Title:	Secretary