X0206 3 2023-05-25 0 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 0001703030 Bain Capital Life Sciences Partners, LP 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 Common Stock 5401926 I See footnote Warrant (right to buy) 5.8069 2022-07-11 2025-06-30 Common Stock 774943 I See footnote Pre-Funded Warrant (right to buy) 0.001 2022-07-11 Common Stock 2739475 I See footnote Represents 2,940,627 shares of Common Stock held by Bain Capital Life Sciences Fund, L.P. ("BCLS Fund I"), 2,160,298 shares of Common Stock held by BCLS I Investco, LP ("BCLS I Investco") and 301,001 shares of Common Stock held by BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS Fund I and BCLS I Investco, the "Bain Capital Life Sciences Entities"). Represents a warrant to purchase 774,943 shares of Common Stock held by BCLS I Investco. Represents a pre-funded warrant to purchase 2,739,475 shares of Common Stock held by BCLS I Investco. BCLS I Investco is prohibited from exercising the warrant to purchase Common Stock referred to in footnote (2) above or the pre-funded warrant to purchase Common Stock referred to in footnote (3) above if the Bain Capital Life Sciences Entities would, in the aggregate, beneficially own more than 9.99% of the total number of shares of Common Stock then issued and outstanding immediately after giving effect to such exercise. The pre-funded warrant does not expire. Bain Capital Life Sciences Partners, LP ("BCLSP") is the general partner of BCLS Fund I. As a result, BCLSP may be deemed to share voting and dispositive power with respect to the securities held by BCLS Fund I. BCLSP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. BCLS I Investco GP, LLC ("BCLS I Investco GP"), whose manager is BCLS Fund I, is the general partner of BCLS I Investco. As a result, each of BCLSP, BCLS Fund I and BCLS I Investco GP may be deemed to share voting and dispositive power with respect to the securities held by BCLS I Investco. Each of BCLSP, BCLS Fund I and BCLS I Investco GP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. Boylston Coinvestors, LLC is the general partner of BCIPLS. Bain Capital Life Sciences Investors, LLC ("BCLSI") is the general partner of BCLSP and governs the investment strategy and decision making process with respect to investments held by BCIPLS. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. BCLSI disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. Bain Capital Life Sciences Investors, LLC, By: /s/ Ricky Sun, Title: Partner 2023-05-30 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/ Ricky Sun, Title: Partner 2023-05-30 Bain Capital Life Sciences Partners, LP, By: Bain Capital Life Sciences Investors, LLC, its general partner, By: /s/ Ricky Sun, Title: Partner 2023-05-30 BCIP Life Sciences Associates, LP, By: Boylston Coinvestors, LLC, its general partner, By: /s/ Ricky Sun, Title: Authorized Signatory 2023-05-30