X0306 4 2021-09-07 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 0001790778 5AM Opportunities I (GP), 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 0001791889 5AM Partners V, 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 2021-09-07 4 S 0 625000 9.70 D 1989575 I See footnotes Common Stock 369688 I See footnotes Shares are held 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 Common Stock held by 5AM V, except to the extent of its or his pecuniary interest therein. Shares are held 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 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 2021-09-09 5AM Opportunities I (GP), LLC, By /s/ Kush Parmar, Managing Member 2021-09-09 5AM Opportunities I, L.P., By: 5AM Opportunities I (GP), LLC, its General Partner, By /s/ Kush Parmar, Managing Member 2021-09-09 5AM Partners V, LLC, By /s/ Scott M. Rocklage, Managing Member 2021-09-09 /s/ Kush Parmar 2021-09-09 /s/ Scott Rocklage 2021-09-09 /s/ Andrew J. Schwab 2021-09-09