X0306 4 2021-12-20 0 0001619856 Caribou Biosciences, Inc. CRBU 0001643875 Braunstein Scott C/O CARIBOU BIOSCIENCES, INC. 2929 7TH STREET, SUITE 105 BERKELEY CA 94710 1 0 0 0 Option to purchase Common Stock 15.16 2021-12-20 4 A 0 27500 0.00 A 2031-12-19 Common Stock 27500 27500 D One-twelfth of the shares subject to this option will vest on each monthly anniversary of the grant date such that the option will be fully vested on December 20, 2022, subject to the reporting person continuing to provide services to the Issuer through each such vesting date. /s/ Barbara G. McClung, as attorney-in-fact 2021-12-21