X0306 4 2019-10-29 0 0001759138 Cabaletta Bio, Inc. CABA 0001487989 Nichtberger Steven C/O CABALETTA BIO, INC. 2929 ARCH STREET, SUITE 600 PHILADELPHIA PA 19104 1 1 0 0 President & CEO Common Stock 2019-10-29 4 C 0 60483 A 786483 D Common Stock 363000 I By 2017 Nichtberger Family Trust Series A-1 Preferred Stock 2019-10-29 4 C 0 90725 D Common Stock 60483 0 D Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date. The reporting person disclaims beneficial ownership of these securities, and the filing of this report is not an admission that the reporting person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose. /s/ Anup Marda, Attorney-in-Fact 2019-10-30