Your Vote Counts! CARIBOU BIOSCIENCES, INC. 2929 7TH STREET SUITE 105 BERKELEY, CA 94710 CARIBOU BIOSCIENCES, INC. 2023 Annual Meeting Vote by June 14, 2023 11:59 PM EDT You invested in CARIBOU BIOSCIENCES, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the stockholder meeting to be held on June 15, 2023. Vote Virtually at the Meeting* June 15, 2023 7:30 a.m., Pacific Daylight Time Virtually at: *Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number V1.1 For complete information and to vote, visit Control # V10238-P92102 Get informed before you vote View the Notice and Proxy Statement and Annual Report on Form 10-K online OR you can receive a free paper or email copy of the materials by requesting prior to June 1, 2023. If you would like to request a copy of the materials for this and/or future stockholder meetings, you may (1) visit, (2) call 1-800-579-1639 or (3) send an email to If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy.

THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. You may view the proxy materials online at or easily request paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. Please follow the instructions on the reverse side to vote on these important matters. Vote at Voting Items Board Recommends V10239-P92102 Prefer to receive an email instead? While voting on, be sure to click “Delivery Settings”. 1. Three Class II director nominees: Nominees: 1c. Nancy Whiting, Pharm.D. 1a. Andrew Guggenhime, M.B.A. 1b. David L. Johnson, M.B.A. For For For 2. Ratification of the appointment of Deloitte & Touche LLP as the independent registered public accounting firm for the fiscal year ending December 31, 2023 The proxies are authorized to vote, in their discretion, upon any other business that may properly come before the Annual Meeting or any continuation(s), adjournment(s), or postponement(s) thereof. For