Sec Form 3 Filing - GORDON CARL L @ ACCELERON PHARMA INC - 2013-09-18

FORM 3 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 Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person GORDON CARL L 2. Issuer Name and Ticker or Trading Symbol ACCELERON PHARMA INC [ XLRN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O ORBIMED ADVISORS LLC, 601 LEXINGTON AVENUE 54TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/18/2013 (Street) NEW YORK, NY10022 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction 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 5,825 I See footnotes ( 1 ) ( 2 ) ( 4 ) Common Stock 2,181 I See footnotes ( 3 ) ( 4 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 Series B Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 1,127,346 I See footnotes ( 1 ) ( 2 ) ( 4 ) Series B Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 422,101 I See footnotes ( 3 ) ( 4 ) Series C Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 175,419 I See footnotes ( 1 ) ( 2 ) ( 4 ) Series C Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 65,680 I See footnotes ( 3 ) ( 4 ) Series D Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 23,442 I See footnotes ( 1 ) ( 2 ) ( 4 ) Series D Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 8,777 I See footnotes ( 3 ) ( 4 ) Series E Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 169,803 I See footnotes ( 1 ) ( 2 ) ( 4 ) Series E Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 63,576 I See footnotes ( 3 ) ( 4 ) Series F Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 38,924 I See footnotes ( 1 ) ( 2 ) ( 4 ) Series F Convertible Preferred Stock ( 6 ) ( 5 ) ( 6 ) Common Stock 14,574 I See footnotes ( 3 ) ( 4 ) Warrants to Purchase Common Stock $ 5.88 ( 7 ) ( 7 ) Common Stock 88,749 I See footnotes ( 1 ) ( 2 ) ( 4 ) Warrants to Purchase Common Stock $ 5.88 ( 7 ) ( 7 ) Common Stock 33,229 I See footnotes ( 3 ) ( 4 ) Warrants to Purchase Common Stock $ 5.88 ( 8 ) ( 8 ) Common Stock 24,151 I See footnotes ( 1 ) ( 2 ) ( 4 ) Warrants to Purchase Common Stock $ 5.88 ( 8 ) ( 8 ) Common Stock 9,042 I See footnotes ( 3 ) ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other GORDON CARL L C/O ORBIMED ADVISORS LLC 601 LEXINGTON AVENUE 54TH FLOOR NEW YORK, NY10022 X Signatures /s/ Douglas Pagan, attorney in fact for Carl Gordon 09/18/2013 Signature of Reporting Person Date

Explanation of Responses:

( 1 )These shares of common stock, shares of Series B Convertible Preferred Stock, shares of Series C Convertible Preferred Stock, shares of Series D Convertible Preferred Stock, shares of Series E Convertible Preferred Stock, shares of Series F Convertible Preferred Stock and warrants to purchase common stock of the registrant are directly owned by OrbiMed Private Investments II, LP (OPI) and may be deemed to be indirectly beneficially owned by OrbiMed Capital GP II LLC (GP II), OrbiMed Advisors LLC (Advisors) and Samuel D. Isaly (Isaly). GP II is the sole general partner of OPI II. Advisors, a registered adviser under the Investment Advisers Act of 1940, as amended, is the sole managing member of GP II. By virtue of such relationships, GP II and Advisors may be deemed to have voting and investment power over the securities held by OPI II noted above. Accordingly, GP II and Advisors may be deemed to have beneficial ownership of such securities. ( 2 )Isaly, a natural person, may also be deemed to have voting and investment power over the securities held by OPI II noted above in his capacity as the managing member of, and owner of a controlling interest in, Advisors. Accordingly, Isaly may be deemed to have beneficial ownership of such securities. ( 3 )These shares of common stock, shares of Series B Convertible Preferred Stock, shares of Series C Convertible Preferred Stock, shares of Series D Convertible Preferred Stock, shares of Series E Convertible Preferred Stock, shares of Series F Convertible Preferred Stock and warrants to purchase common stock of the registrant are directly owned by OrbiMed Private Investments II (QP), LP (OPI II QP) and may be deemed to be indirectly beneficially owned by GP II, Advisors and Isaly. GP II is the sole general partner of OPI II QP. Advisors is the sole managing member of GP II. Isaly is the managing member of, and owner of a controlling interest in, Advisors. By virtue of such relationships, GP II, Advisors and Isaly may be deemed to have voting and investment power over the securities held by OPI II QP noted above. Accordingly, GP II, Advisors and Isaly may be deemed to have beneficial ownership of such securities. ( 4 )GP II, Advisors and Isaly have designated a representative, currently Carl L. Gordon, a member of Advisors, to serve on the Issuers board of directors. Each of GP II, Advisors, Isaly and Carl L. Gordon disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (Exchange Act), except to the extent of its or his pecuniary interest therein, if any. This report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 of the Exchange Act or for any other purpose. ( 5 )The Series A Convertible Preferred Stock, Series B Convertible Preferred Stock, Series C Convertible Preferred Stock, Series D Convertible Preferred Stock, Series E Convertible Preferred Stock and Series F Convertible Preferred Stock are each convertible into Common Stock at any time at the holders election and will automatically convert upon the consummation of a qualified public offering of the registrant. ( 6 )Each share of preferred stock is convertible into Common Stock at a ratio of 1 share of Common Stock per share of preferred stock, except for the Series E Convertible Preferred Stock, which may convert into Common Stock at a ratio greater than 1-to-1, based on a formula driven by the date on which the issuer completes an IPO and the price of such offering, as described at page 37 of the issuers Amended Form S-1 registration statement filed September 6, 2013, File No. 333-190417. The conversion ratio used for the Series E Convertible Preferred Stock is based on an assumed closing date of September 24, 2013. There is no expiration date and no additional consideration is required upon conversion for any series of convertible preferred stock. ( 7 )The warrants to purchase Common Stock are exercisable at any time at the holders election and have an expiration date on June 10, 2020. ( 8 )The warrants to purchase Common Stock are exercisable at any time at the holders election and have an expiration date on July 9, 2020.

Remarks: Exhibit List Exhibit 24 Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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