X0306 4 2019-10-29 0 0001759138 Cabaletta Bio, Inc. CABA 0001674324 5AM Ventures V, L.P. 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001791889 5AM Partners V, LLC 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001753000 5AM Opportunities I, L.P. 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001790778 5AM Opportunities I (GP), LLC 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001664281 PARMAR KUSH 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001219014 ROCKLAGE SCOTT M 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 0001598549 Schwab Andrew J. 501 2ND STREET, SUITE 350 SAN FRANCISCO CA 94107 0 0 1 0 Common Stock 2019-10-29 4 C 0 3214721 A 3214721 I See footnotes Common Stock 2019-10-29 4 P 0 454545 11.00 A 454545 I See footnotes Series A Preferred Stock 2019-10-29 4 C 0 3146551 D Common Stock 2097700 0 I See footnotes Series B Preferred Stock 2019-10-29 4 C 0 1675532 D Common Stock 1117021 0 I See footnotes These shares of Series A Preferred Stock and Series B Preferred Stock (collectively, "Preferred Stock") automatically converted into shares of the Issuer's Voting Common Stock ("Common Stock"), on a 1-for-1.5 basis, immediately prior to the completion of the Issuer's initial public offering for no additional consideration. The Preferred Stock had no expiration date. Shares are held directly by 5AM Ventures V, L.P. ("5AM V"). 5AM Partners V, LLC ("5AM Partners") is the sole general partner of 5AM V. Dr. Kush Parmar, Andrew J. Schwab and Dr. Scott M. Rocklage are managing members of 5AM Partners and may be deemed to have shared voting and investment power over the shares beneficially owned by 5AM V. Each of 5AM Partners, Dr. Parmar, Mr. Schwab and Dr. Rocklage disclaims beneficial ownership of the shares of Preferred Stock held directly by 5AM V, except to the extent of its or his pecuniary interest therein. Shares are held directly by 5AM Opportunities I, L.P. ("Opportunities"). 5AM Opportunities I (GP), LLC ("Opportunities GP") is the sole general partner of Opportunities. Andrew J. Schwab and Dr. Kush Parmar are managing members of Opportunities GP and may be deemed to have shared voting and investment power over the shares beneficially owned by Opportunities. Each of Opportunities GP, Mr. Schwab and Dr. Parmar disclaims beneficial ownership of the shares of Common Stock held directly by Opportunities, except to the extent of its or his pecuniary interest therein. 5AM VENTURES V, L.P. By: 5AM Partners V, LLC, its General Partner By: /s/ Scott M. Rocklage Managing Member 2019-10-31 5AM PARTNERS V, LLC By: /s/ Scott M. Rocklage Managing Member 2019-10-31 5AM OPPORTUNITIES I, L.P. By: 5AM Opportunities I (GP), LLC, its General Partner By: /s/ Kush Parmar Managing Member 2019-10-31 5AM OPPORTUNITIES I (GP), LLC By: /s/ Kush Parmar Managing Member 2019-10-31 /s/ Kush Parmar 2019-10-31 /s/ Scott Rocklage 2019-10-31 /s/ Andrew J. Schwab 2019-10-31