X0306 4 2022-01-31 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 2022-01-31 4 M 0 50000 1.01 A 836483 D Common Stock 363000 I By 2017 Nichtberger Family Trust Stock Option (Right to Buy) 1.01 2022-01-31 4 M 0 50000 0.00 D 2028-10-28 Common Stock 50000 229677 D 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. On October 29, 2018, the reporting person was granted a stock option to purchase 279,677 shares of common stock. The shares vest and become exercisable over four years, with 25% vested on October 11, 2019, and the remaining shares vesting in 36 equal monthly installments thereafter. On January 31, 2022 the reporting person exercised this option for 50,000 shares. By: /s/ Michael Gerard, Attorney-in-Fact 2022-02-02