Sec Form 3 Filing - Fischesser Ryan @ Caribou Biosciences, Inc. - 2024-09-27

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Fischesser Ryan 2. Issuer Name and Ticker or Trading Symbol Caribou Biosciences, Inc. [ CRBU] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) VP of Finance and Controller (Last) (First) (Middle) C/O CARIBOU BIOSCIENCES, INC., 2929 7TH STREET, SUITE 105 3. Date of Earliest Transaction (MM/DD/YY) 09/27/2024 (Street) BERKELEY, CA94710 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 93,854 ( 1 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Option to purchase Common Stock $ 4.11 ( 2 ) 03/29/2031 Common Stock 13,065 D Option to purchase Common Stock $ 15.16 ( 3 ) 12/19/2031 Common Stock 40,000 D Option to purchase Common Stock $ 6.12 ( 4 ) 02/20/2033 Common Stock 48,000 D Option to purchase Common Stock $ 6.81 ( 5 ) 02/19/2034 Common Stock 36,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Fischesser Ryan C/O CARIBOU BIOSCIENCES, INC. 2929 7TH STREET, SUITE 105 BERKELEY, CA94710 VP of Finance and Controller Signatures /s/ Barbara G. McClung, as attorney-in-fact 10/04/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents: (i) 70,454 shares of Common Stock, par value $0.0001 per share ("Common Stock"), of Caribou Biosciences, Inc. (the "Issuer") beneficially owned by the reporting person, and (ii) 23,400 Restricted Stock Units ("RSUs") that will vest in four equal annualinstallments beginning on February 20, 2025 and that are settleable in shares of Common Stock within 30 days after each vesting date, subject to the reporting person's continued services to the Issuer through the applicable vesting dates. ( 2 )1/4th of the 27,270 shares originally subject to this option vested on January 1, 2022 and an additional 1/48th of the aggregate number of shares originally subject to the option vest on the corresponding day of each month thereafter until the option is fully vested on January 1, 2025, subject to the reporting person's continued service to the Issuer through the applicable vesting dates. ( 3 )The shares subject to this option vest in equal monthly installments starting on January 20, 2022, the first monthly anniversary of the grant date, until the option is fully vested on December 20, 2025, subject to the reporting person's continued service to the Issuer through the applicable vesting dates. ( 4 )The shares subject to this option vest in equal monthly installments starting on March 21, 2023, the first monthly anniversary of the grant date, until the option is fully vested on February 21, 2027, subject to the reporting person's continued service to the Issuer through the applicable vesting dates. ( 5 )25% of the shares subject to this option will vest upon February 20, 2025, the one-year anniversary of the grant date, and 1/48th will vest monthly over the 36-month period thereafter, until the option is fully vested on February 20, 2028, subject to the reporting person's continued service to the Issuer through the applicable vesting dates.

Remarks: Exhibit 24 - Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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