X0306 4 2020-07-28 1 0001528115 Annexon, Inc. ANNX 0001703031 Bain Capital Life Sciences Investors, LLC 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001687968 Bain Capital Life Sciences Fund, L.P. 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001702921 BCIP Life Sciences Associates, LP 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001578965 Koppel Adam C/O BAIN CAPITAL LIFE SCIENCES INVESTORS LLC, 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001703030 Bain Capital Life Sciences Partners, LP 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 0001702957 Schwartz Jeffrey Lawrence C/O BAIN CAPITAL LIFE SCIENCES INVESTORS LLC, 200 CLARENDON STREET BOSTON MA 02116 0 0 1 0 Common Stock 2020-07-28 4 C 0 2522385 A 2522385 I See Footnotes Common Stock 2020-07-28 4 C 0 319243 A 2841628 I See Footnotes Common Stock 2020-07-28 4 P 0 400000 17.00 A 3241628 I See Footnotes Series C Preferred Stock 2020-07-28 4 C 0 22222221 D Common Stock 2522385 0 I See Footnotes Series D Preferred Stock 2020-07-28 4 C 0 2812543 D Common Stock 319243 0 I See Footnotes Each share of Series C Preferred Stock ("Series C Stock") and Series D Preferred Stock ("Series D Stock") automatically converted on a 1-for-8.81 basis into the Issuer's Common Stock immediately prior to the closing of the Issuer's initial public offering. Represents 20,158,775 shares of Series C Stock held of record by Bain Capital Life Sciences Fund, L.P. ("BCLS") and 2,063,446 shares of Series C Stock held of record by BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities"). Represents 2,551,384 shares of Series D Stock held of record by BCLS and 261,159 shares of Series D Stock held of record by BCIPLS. Represents 362,858 and 37,142 shares of the Issuer's Common Stock purchased by BCLS and BCIPLS, respectively, in the Issuer's initial public offering. Bain Capital Life Sciences Partners, LP ("BCLSP") is the general partner of BCLS. As a result, BCLSP may be deemed to share voting and dispositive power with respect to the securities held by BCLS. BCLSP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. Bain Capital Life Sciences Investors, LLC ("BCLSI"), whose managers are Jeffrey Schwartz and Adam Koppel, is the general partner of BCLSP and governs the investment strategy and decision-making process with respect to investments held by BCIPLS, whose general partner is Boylston Coinvestors, LLC. As a result, each of BCLSI, Mr. Schwartz and Dr. Koppel may be deemed to share voting and dispositive power over the shares held by the Bain Capital Life Sciences Entities. BCLSI, Mr. Schwartz and Dr. Koppel each disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein. BAIN CAPITAL LIFE SCIENCES INVESTORS, LLC, By: /s/ Jeffrey Schwartz, Name: Jeffrey Schwartz, Title: Managing Director 2020-07-28 BAIN CAPITAL LIFE SCIENCES PARTNERS, LP, By: Bain Capital Life Sciences Investors, LLC, its general partner, By: /s/ Jeffrey Schwartz, Name: Jeffrey Schwartz, Title: Managing Director 2020-07-28 BAIN CAPITAL LIFE SCIENCES FUND, L.P., By: Bain Capital Life Sciences Partners, LP, its general partner, By: Bain Capital Life Sciences Investors, LLC, its general partner, By: /s/ Jeffrey Schwartz, Name: Jeffrey Schwartz, Title: Managing Director 2020-07-28 BCIP LIFE SCIENCES ASSOCIATES, LP, By: Boylston Coinvestors, LLC, its general partner, By: /s/ Jeffrey Schwartz, Name: Jeffrey Schwartz, Title: Authorized Signatory 2020-07-28 /s/ Adam Koppel 2020-07-28 /s/ Jeffrey Schwartz 2020-07-28