X0206 3 2013-09-18 0 0001280600 ACCELERON PHARMA INC XLRN 0001055951 ORBIMED ADVISORS LLC C/O ORBIMED ADVISORS LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 0001055949 ISALY SAMUEL D 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 0001281668 ORBIMED CAPITAL GP II LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 Common Stock 5825 I See footnote Common Stock 2181 I See footnote Series B Convertible Preferred Stock Common Stock 1127346 I See footnote Series B Convertible Preferred Stock Common Stock 422101 I See footnote Series C Convertible Preferred Stock Common Stock 175419 I See footnote Series C Convertible Preferred Stock Common Stock 65680 I See footnote Series D Convertible Preferred Stock Common Stock 23442 I See footnote Series D Convertible Preferred Stock Common Stock 8777 I See footnote Series E Convertible Preferred Stock Common Stock 169803 I See footnote Series E Convertible Preferred Stock Common Stock 63576 I See footnote Series F Convertible Preferred Stock Common Stock 38924 I See footnote Series F Convertible Preferred Stock Common Stock 14574 I See footnote Warrants to Purchase Common Stock 5.88 Common Stock 88749 I See footnote Warrants to Purchase Common Stock 5.88 Common Stock 33229 I See footnote Warrants to Purchase Common Stock 5.88 Common Stock 24151 I See footnote Warrants to Purchase Common Stock 5.88 Common Stock 9042 I See footnote 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 II") 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. 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. 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. This report on Form 3 is jointly filed by GP II, Advisors and Isaly. GP II, Advisors and Isaly have designated a representative, currently Carl L. Gordon, a member of Advisors, to serve on the Issuer's 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 (the "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. 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 holder's election and will automatically convert upon the consummation of a qualified public offering of the registrant. 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 issuer's 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. The warrants to purchase Common Stock are exercisable at any time at the holder's election and have an expiration date on June 10, 2020. The warrants to purchase Common Stock are exercisable at any time at the holder's election and have an expiration date on July 9, 2020. /s/ Samuel D. Isaly 2013-09-18