Statement of Changes in Beneficial Ownership (4)

FORM 4

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

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3235-0287

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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person * Veness Adam M	2. Issuer Name and Ticker or Trading Symbol ACCELERON PHARMA INC [ XLRN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director                    _____ 10% Owner __X__ Officer (give title below)    _____ Other (specify below) SVP, General Counsel and Sec.
(Last)          (First)          (Middle) 128 SIDNEY STREET	3. Date of Earliest Transaction (MM/DD/YYYY) 9/21/2021
(Street) CAMBRIDGE, MA 02139 (City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	9/21/2021		M(1)		5200	A	$30.17	24123	D
Common Stock	9/21/2021		M(1)		1450	A	$41.20	25573	D
Common Stock	9/21/2021		S(1)		6650	D	$150.05 (2)	18923	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Option to Purchase Common Stock	$30.17	9/21/2021		M (1)			5200	(3)	3/2/2027	Common Stock	5200	$0	0	D
Option to Purchase Common Stock	$41.20	9/21/2021		M (1)			1450	(4)	1/8/2025	Common Stock	1450	$0	0	D

Explanation of Responses:
(1)	The reported transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person.
(2)	The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $150.00 to $150.36 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (2) to this Form 4.
(3)	The shares of common stock underlying this stock option award vested in equal quarterly installments over the four years after January 1, 2017.
(4)	The shares of common stock underlying this stock option award vested in equal quarterly installments over the four years after January 1, 2015.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Veness Adam M 128 SIDNEY STREET CAMBRIDGE, MA 02139			SVP, General Counsel and Sec.

Signatures
/s/ Adam M. Veness		9/22/2021
**Signature of Reporting Person		Date