EX-10.46





 Exhibit 10.46 

CARIBOU BIOSCIENCES, INC. 

2021 EMPLOYEE STOCK PURCHASE PLAN 

ADOPTED BY THE BOARD OF 
DIRECTORS: July 11, 2021 

APPROVED BY THE STOCKHOLDERS:
                , 2021 

IPO DATE:                , 2021

 1. GENERAL; PURPOSE. 

(a) The Plan provides a means by which Eligible Employees of the Company and certain designated Related Corporations may be given an
opportunity to purchase shares of Common Stock. The Plan permits the Company to grant a series of Purchase Rights to Eligible Employees under an Employee Stock Purchase Plan. In addition, the Plan permits the Company to grant a series of Purchase
Rights to Eligible Employees, which rights do not meet the requirements of an Employee Stock Purchase Plan. 
 (b) The Plan includes
two components: a Section 423 Component and a Non-Section 423 Component, which may be operated in the discretion of the Board. The Company intends the 423 Component to qualify as an Employee
Stock Purchase Plan, which will be construed in a manner that is consistent with the requirements of Section 423 of the Code. Except as otherwise provided in the Plan or determined by the Board, if operated,
the Non-Section 423 Component will operate and be administered in the same manner as the 423 Component. 

(c) The Plan provides eligible employees of the Company and Related Corporations with a means of acquiring an equity interest in the
Company through payroll deductions and cash Contributions. The purpose of the Plan is to secure the services of new employees, to retain the services of existing employees, and to provide incentives for such individuals to exert maximum efforts
toward the success of the Company and its Related Corporations. 
 2. ADMINISTRATION. 

(a) The Board or the Committee will administer the Plan. References herein to the Board shall be deemed to refer to the Committee except
where context dictates otherwise. 
 (b) The Board will have the power, subject to, and within the limitations of, the express
provisions of the Plan: 
 (i) To determine how and when Purchase Rights will be granted and the provisions of each Offering (which
need not be identical). 
 (ii) To designate from time to time (A) which Related Corporations of the Company will be eligible to
participate in the Plan, (B) whether such Related Corporations will participate in the 423 Component or the Non-Section 423 Component, and (C) to the extent that the Company makes separate
Offerings under the 423 Component, in which Offering the Related Corporations in the 423 Component will participate. 
 (iii) To
construe and interpret the Plan and Purchase Rights, and to establish, amend, and revoke rules and regulations for its administration. The Board, in the exercise of this power, may correct any defect, omission, or inconsistency in the Plan,
Offering, or Purchase Period in a manner and to the extent it deems necessary or expedient to make the Plan fully effective. 
 (iv)
To settle all controversies regarding the Plan and Purchase Rights granted under the Plan. 
 (v) To suspend or terminate the Plan at
any time as provided in Section 12. 
 (vi) To amend the Plan at any time as provided in Section 12. 












 (vii) Generally, to exercise such powers and to perform such acts as it deems
necessary or expedient to promote the best interests of the Company and its Related Corporations and to carry out the intent that the Plan be treated as an Employee Stock Purchase Plan with respect to the 423 Component. 

(viii) To adopt such rules, procedures, and sub-plans as are necessary or appropriate
to permit or facilitate participation in the Plan by Employees who are foreign nationals or employed or located outside the United States. Without limiting the generality of, and consistent with, the foregoing, the Board specifically is authorized
to adopt rules, procedures, and sub-plans regarding, without limitation, eligibility to participate in the Plan, the definition of eligible “earnings,” handling and making of Contributions,
establishment of bank or trust accounts to hold Contributions, payment of interest, conversion of local currency, obligations to pay payroll tax, determination of beneficiary designation requirements, withholding procedures, and handling of share
issuances, any of which may vary according to applicable requirements, and which, if applicable to a Related Corporation designated for participation in the Non-423 Component, do not have to comply
with the requirements of Section 423 of the Code. 
 (c) The Board may delegate some or all of the administration of the Plan to
a Committee or Committees from time to time in accordance with the terms provided in a Board resolution or determination. If administration is delegated to a Committee, the Committee will have, in connection with the administration of the Plan, the
powers theretofore possessed by the Board that have been delegated to the Committee, including the power to delegate to a subcommittee any of the administrative powers the Committee is authorized to exercise (and references in this Plan to the Board
will thereafter be to the Committee or subcommittee), subject, however, to such resolutions and determinations, not inconsistent with the provisions of the Plan, as may be adopted from time to time by the Board. The Board may retain the authority to
concurrently administer the Plan with the Committee and may, at any time, revest in the Board some or all of the powers previously delegated. 

(d) All determinations, interpretations, and constructions made by the Board in good faith will not be subject to review by any person
and will be final, binding, and conclusive on all persons. 
 3.
SHARES OF COMMON STOCK SUBJECT TO THE PLAN. 

(a) Subject to the provisions of Section 11(a) relating to Capitalization Adjustments, a total of 511,000 shares of Common Stock is
reserved for issuance under this Plan. In addition, on each January 1 for the ten (10) calendar years immediately after the first Offering Date, the aggregate number of shares of Common Stock reserved for issuance under the Plan will be
increased automatically by the number of shares equal to one percent (1%) of the total number of outstanding shares of the Common Stock on the immediately preceding December 31 (rounded down to the nearest whole share); provided that the Board
or the Committee may in its sole discretion reduce the amount of the increase in any particular year; and provided, further, that the aggregate number of shares of Common Stock issued over the term of this Plan will not exceed 10,000,000 shares. For
the avoidance of doubt, up to the maximum number of shares of Common Stock reserved under this Section 3(a) may be used to satisfy purchases of Common Stock under the 423 Component, and any remaining portion of such maximum number of shares may
be used to satisfy purchases of Common Stock under the Non-423 Component. 
 (b) If any
Purchase Right granted under the Plan terminates without having been exercised in full, the shares of Common Stock represented by and not purchased under such Purchase Right will again become available for issuance under the Plan. 

(c) The stock purchasable under the Plan will be shares of authorized but unissued or reacquired Common Stock, including shares
repurchased by the Company on the open market. 
 4. GRANT OF PURCHASE RIGHTS;
OFFERING. 
 (a) The Board may from time to time grant, or provide for the grant, of Purchase Rights to Eligible
Employees under an Offering (which may consist of one or more Purchase Periods) on an Offering Date or Offering Dates selected by the Board. Each Offering will be in such form and will contain such terms and conditions as the Board will deem
appropriate, and, with respect to the 423 Component, will comply with the requirement of Section 423(b)(5) of the Code that all Employees granted Purchase Rights will have the same rights and privileges.


  
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Offerings may be consecutive or overlapping. The terms and conditions of an Offering shall be incorporated by reference into the Plan and treated as part of the Plan. The provisions of separate
Offerings need not be identical, but each Offering will include (through incorporation of the provisions of this Plan by reference in the document comprising the Offering or otherwise) the period during which the Offering will be effective, which
period will not exceed 27 months beginning with the Offering Date, and the substance of the provisions contained in Sections 5 through 8, inclusive. 

(b) If a Participant has more than one Purchase Right outstanding under the Plan, unless they otherwise indicates in forms delivered to
the Company: (i) each form will apply to all of his or her Purchase Rights under the Plan, and (ii) a Purchase Right with a lower exercise price (or an earlier-granted Purchase Right, if different Purchase Rights have identical exercise
prices) will be exercised to the fullest possible extent before a Purchase Right with a higher exercise price (or a later-granted Purchase Right if different Purchase Rights have identical exercise prices) will be exercised. 

(c) The Board will have the discretion to structure an Offering so that if the Fair Market Value of a share of Common Stock on the
first Trading Day of a new Purchase Period within that Offering is less than or equal to the Fair Market Value of a share of Common Stock on the Offering Date for that Offering, then (i) that Offering will terminate immediately as of that first
Trading Day, and (ii) the Participants in such terminated Offering will be automatically enrolled in a new Offering beginning on the first Trading Day of such new Purchase Period. 

5. ELIGIBILITY. 

(a) Purchase Rights may be granted only to Employees of the Company or, as the Board may designate in accordance with Section 2(b),
to Employees of a Related Corporation. Except as provided in Section 5(b) or as required by Applicable Law, an Employee will not be eligible to be granted Purchase Rights unless, on the Offering Date, the Employee has been in the employ of the
Company or the Related Corporation, as the case may be, for such continuous period preceding such Offering Date as the Board may require, but in no event will the required period of continuous employment be equal to or greater than two years. In
addition, the Board may (unless prohibited by law) provide that no Employee will be eligible to be granted Purchase Rights under the Plan unless, on the Offering Date, such Employee’s customary employment with the Company or the Related
Corporation is more than 20 hours per week and more than five months per calendar year or such other criteria as the Board may determine consistent with Section 423 of the Code with respect to the 423 Component. The Board may also exclude from
participation in the Plan or any Offering Employees who are (i) “highly compensated employees” of the Company or a Related Corporation (within the meaning of Section 414(q) of the Code), or (ii) “highly compensated
employees” with compensation above a specified level, who is an officer and/or is subject to the disclosure requirements of Section 16(a) of the Exchange Act. 

(b) The Board may provide that each person who, during the course of an Offering, first becomes an Eligible Employee will, on a date or
dates specified in the Offering which coincides with the day on which such person becomes an Eligible Employee or which occurs thereafter, receive a Purchase Right under that Offering, which Purchase Right will thereafter be deemed to be a part of
that Offering. Such Purchase Right will have the same characteristics as any Purchase Rights originally granted under that Offering, as described herein, except that: 

(i) the date on which such Purchase Right is granted will be the “Offering Date” of such Purchase Right for all purposes,
including determination of the exercise price of such Purchase Right; 
 (ii) the period of the Offering with respect to such
Purchase Right will begin on its Offering Date and end coincident with the end of such Offering; and 
 (iii) the Board may provide
that if such person first becomes an Eligible Employee within a specified period of time before the end of the Offering, they will not receive any Purchase Right under that Offering. 

(c) No Employee will be eligible for the grant of any Purchase Rights if, immediately after any such Purchase Rights are granted, such
Employee owns stock possessing five percent (5%) or more of the total combined voting power or value of all classes of stock of the Company or of any Related Corporation. For purposes of this Section 5(c), the rules of Section 424(d) of
the Code will apply in determining the stock ownership of any Employee, and stock which such Employee may purchase under all outstanding Purchase Rights and options will be treated as stock owned by such Employee. 

  
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 (d) As specified by Section 423(b)(8) of the Code, an Eligible Employee may be
granted Purchase Rights only if such Purchase Rights, together with any other rights granted under all Employee Stock Purchase Plans of the Company and any Related Corporations, do not permit such Eligible Employee’s rights to purchase stock of
the Company or any Related Corporation to accrue at a rate which, when aggregated, exceeds $25,000 in Fair Market Value of such stock (determined at the time such rights are granted, and which, with respect to the Plan, will be determined as of
their respective Offering Dates) for each calendar year in which such rights are outstanding at any time. 
 (e) Unless otherwise
determined to be ineligible to participate under the preceding sections, Officers of the Company and any designated Related Corporation, if they are otherwise Eligible Employees, will be eligible to participate in Offerings under the Plan. 

(f) Notwithstanding anything in this Section 5 to the contrary, in the case of an Offering under
the Non-Section 423 Component, an Eligible Employee (or group of Eligible Employees) may be excluded from participation in the Plan or an Offering if the Board has determined, in its sole discretion,
that participation of such Eligible Employee(s) is not advisable or practical for any reason. 
 6. PURCHASE RIGHTS;
PURCHASE PRICE. 
 (a) On each Offering Date, each Eligible Employee, pursuant to an Offering
made under the Plan, will be granted a Purchase Right to purchase up to that number of shares of Common Stock which may be purchased with payroll deductions to be accumulated on behalf of such Eligible Employee assuming payroll deductions at a rate
of twenty-five percent (25% ) of such Eligible Employee’s earnings (or such other lesser percentage or maximum dollar amount designated by the Board, and as defined by the Board in each Offering) during the period that begins on the Offering
Date (or such later date as the Board determines for a particular Offering) and ends on the date stated in the Offering, which date will be no later than the end of the Offering, and a purchase price equal to eighty-five percent (85%) of the Fair
Market Value as of the Offering Date. 
 (b) The Board will establish one or more Purchase Dates during an Offering on which Purchase
Rights granted for that Offering will be exercised and shares of Common Stock will be purchased in accordance with such Offering. 

(c) In connection with each Offering made under the Plan, the Board may specify (i) a maximum number of shares of Common Stock
that may be purchased by any Participant on any Purchase Date during such Offering, (ii) a maximum aggregate number of shares of Common Stock that may be purchased by all Participants pursuant to such Offering, and/or (iii) a maximum
aggregate number of shares of Common Stock that may be purchased by all Participants on any Purchase Date under the Offering. If the aggregate purchase of shares of Common Stock issuable upon exercise of Purchase Rights granted under the Offering
would exceed any such maximum aggregate number, then, in the absence of any Board action otherwise, a pro rata (based on each Participant’s accumulated Contributions) allocation of the shares of Common Stock (rounded down to the nearest whole
share) available will be made in as nearly a uniform manner as will be practicable and equitable. 
 (d) The purchase price of shares
of Common Stock acquired pursuant to Purchase Rights will be not less than the lesser of: 
 (i) an amount equal to eighty-five
percent (85%) of the Fair Market Value of the shares of Common Stock on the Offering Date; or 
 (ii) an amount equal to eighty-five
percent (85%) of the Fair Market Value of the shares of Common Stock on the applicable Purchase Date. 

  
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 7. PARTICIPATION; WITHDRAWAL; TERMINATION. 

(a) An Eligible Employee may elect to participate in an Offering and authorize payroll deductions as the means of making Contributions
by completing and delivering to the Company, within the time specified in the Offering, an enrollment form, provided by the Company. The enrollment form will specify the amount of Contributions not to exceed fifteen percent (15%) and not less than
one percent (1%) of such Eligible Employee’s earnings (as defined by the Board in each Offering) during the Offering, or such other maximum amount specified by the Board. Each Participant’s Contributions will be credited to a bookkeeping
account for such Participant under the Plan and will be deposited with the general funds of the Company except where Applicable Law requires that Contributions be deposited with a third party. If permitted in the Offering, a Participant may begin
such Contributions with the first payroll occurring on or after the Offering Date (or, in the case of a payroll date that occurs after the end of the prior Offering but before the Offering Date of the next new Offering, Contributions from such
payroll will be included in the new Offering). If permitted in the Offering, and subject to any limitations imposed, a Participant may thereafter reduce (including to zero) or increase their Contributions. If required under Applicable Law or if
specifically provided in the Offering, in addition to or instead of making Contributions by payroll deductions, a Participant may make Contributions through payment by cash, check, or wire transfer prior to a Purchase Date and within the time period
specified by the Board for the Offering. 
 (b) During an Offering, a Participant may cease making Contributions and withdraw from
the Offering by delivering to the Company a withdrawal form provided by the Company. The Company may impose a deadline before a Purchase Date for withdrawing. Upon such withdrawal, such Participant’s Purchase Right in that Offering will
immediately terminate and the Company will distribute as soon as practicable to such Participant all of their accumulated but unused Contributions and such Participant’s Purchase Right in that Offering shall thereupon terminate. A
Participant’s withdrawal from that Offering will have no effect upon their eligibility to participate in any other Offerings under the Plan, but such Participant will be required to deliver a new enrollment form to participate in subsequent
Offerings. 
 (c) Unless otherwise required by Applicable Law, Purchase Rights granted pursuant to any Offering under the Plan will
terminate immediately if the Participant either (i) is no longer an Employee for any (or no) reason (subject to any post-employment participation period required by law) or (ii) is otherwise no longer eligible to participate. The Company
will distribute as soon as practicable to such individual all of their accumulated but unused Contributions. 
 (d) Unless otherwise
determined by the Board, a Participant whose employment transfers or whose employment terminates with an immediate rehire (with no break in service) by or between the Company and a Related Corporation that has been designated for participation in
the Plan will not be treated as having terminated employment for purposes of participating in the Plan or an Offering; however, if a Participant transfers from an Offering under the 423 Component to an Offering under
the Non-Section 423 Component, the exercise of the Participant’s Purchase Right will be qualified under the 423 Component only to the extent such exercise complies with Section 423 of the
Code. If a Participant transfers from an Offering under the Non-Section 423 Component to an Offering under the 423 Component, the exercise of the Purchase Right will
remain non-qualified under the Non-Section 423 Component. The Board may establish different and additional rules governing transfers between separate
Offerings within the 423 Component and between Offerings under the 423 Component and Offerings under the Non-Section 423 Component. 

(e) During a Participant’s lifetime, Purchase Rights will be exercisable only by such Participant. Purchase Rights are not
transferable by a Participant, except by will, by the laws of descent and distribution, or, if permitted by the Company, by a beneficiary designation as described in Section 10. 

(f) Unless otherwise specified in the Offering or as required by Applicable Law, the Company will have no obligation to pay interest on
Contributions. 
 8. EXERCISE OF PURCHASE RIGHTS. 

(a) On each Purchase Date, each Participant’s accumulated Contributions will be applied to the purchase of shares of Common
Stock, up to the maximum number of shares of Common Stock permitted by the Plan and the applicable Offering, at the purchase price specified in the Offering. No fractional shares will be issued unless specifically provided for in the Offering. 

  
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 (b) Any amount remaining in a Participant’s account at the end of an Offering
solely by reason of the inability to purchase a fractional share will be carried forward to the next Offering; any other balance remaining in a Participant’s account at the end of an Offering will not roll over to the next Offering and will be
refunded to the Participant promptly without interest (unless otherwise required by Applicable Law). 
 (c) No Purchase Rights may be
exercised to any extent unless the shares of Common Stock to be issued upon such exercise under the Plan are covered by an effective registration statement pursuant to the Securities Act and the Plan is in material compliance with all applicable
U.S. federal and state, foreign, and other securities, exchange control, and other laws applicable to the Plan. If on a Purchase Date the shares of Common Stock are not so registered or the Plan is not in such compliance, no Purchase Rights will be
exercised on such Purchase Date, and the Purchase Date will be delayed until the shares of Common Stock are subject to such an effective registration statement and the Plan is in material compliance, except that the Purchase Date will in no event be
more than 27 months from the Offering Date. If, on the Purchase Date, as delayed to the maximum extent permissible, the shares of Common Stock are not registered and the Plan is not in material compliance with all Applicable Laws, as determined by
the Company in its sole discretion, no Purchase Rights will be exercised and all accumulated but unused Contributions will be distributed to the Participants without interest (unless the payment of interest is otherwise required by Applicable Law).

 9. COVENANTS OF THE COMPANY. 

The Company will seek to obtain from each U.S. federal or state, foreign, or other regulatory commission or agency having jurisdiction over the
Plan such authority as may be required to grant Purchase Rights and issue and sell shares of Common Stock thereunder unless the Company determines, in its sole discretion, that doing so would cause the Company to incur costs that are unreasonable or
a significant burden. If, after commercially reasonable efforts, the Company is unable to obtain the authority that counsel for the Company deems necessary for the grant of Purchase Rights or the lawful issuance and sale of Common Stock under the
Plan, and at a commercially reasonable cost, the Company will be relieved from any liability for failure to grant Purchase Rights and/or to issue and sell Common Stock upon exercise of such Purchase Rights. 

10. DESIGNATION OF BENEFICIARY. 

(a) The Company may, but is not obligated to, permit a Participant to submit a form designating a beneficiary who will receive any
shares of Common Stock and/or Contributions from the Participant’s account under the Plan if the Participant dies before such shares and/or Contributions are delivered to the Participant. The Company may, but is not obligated to, permit the
Participant to change such designation of beneficiary. Any such designation and/or change must be on a form approved by the Company. 

(b) If a Participant dies, and in the absence of a valid beneficiary designation, the Company will deliver any shares of Common Stock
and/or Contributions to the executor or administrator of the estate of the Participant. If no executor or administrator has been appointed (to the knowledge of the Company), the Company, in its sole discretion, may deliver such shares of Common
Stock and/or Contributions, without interest (unless the payment of interest is otherwise required by Applicable Law), to the Participant’s spouse, dependents, or relatives, or if no spouse, dependent, or relative is known to the Company, then
to such other person as the Company may designate. 
 11.
ADJUSTMENTS UPON CHANGES IN COMMON STOCK. 

In the event of a Capitalization Adjustment, the Board will appropriately and proportionately adjust: (i) the class(es) and maximum number
of securities subject to the Plan pursuant to Section 3(a), (ii) the class(es) and maximum number of securities by which the share reserve is to increase automatically each year pursuant to Section 3(a), (iii) the class(es) and number of
securities subject to, and the purchase price applicable to, outstanding Offerings and Purchase Rights, and (iv) the class(es) and number of securities that are the subject of the purchase limits under each ongoing Offering. The Board will make
these adjustments, and its determination will be final, binding, and conclusive.

  
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 12. AMENDMENT,
TERMINATION, OR SUSPENSION OF THE PLAN. 

(a) The Board may amend the Plan at any time in any respect the Board deems necessary or advisable. However, except as provided in
Section 11(a) relating to Capitalization Adjustments, stockholder approval will be required for any amendment of the Plan for which stockholder approval is required by Applicable Law. 

(b) The Board may suspend or terminate the Plan at any time. No Purchase Rights may be granted under the Plan while the Plan is
suspended or after it is terminated. In the event of a corporate transaction affecting the Company or its Related Corporations, the Board may determine to truncate any then outstanding Offering, and the Participants’ accumulated Contributions
will be used to purchase shares of Common Stock (rounded down to the nearest whole share) within ten business days prior to the corporate transaction under the outstanding Purchase Rights, and the Purchase Rights will terminate immediately after
such purchase, or the Board may require any surviving corporation or acquiring corporation (or the surviving or acquiring corporation’s parent company) to assume or continue outstanding Purchase Rights or substitute similar rights (including a
right to acquire the same consideration paid to the stockholders in the corporate transaction) for outstanding Purchase Rights. 
 Any
benefits, privileges, entitlements, and obligations under any outstanding Purchase Rights granted before an amendment, suspension, or termination of the Plan will not be materially impaired by any such amendment, suspension, or termination except
(i) with the consent of the person to whom such Purchase Rights were granted, (ii) without the consent of a person to whom such Purchase Rights were granted, as necessary to comply with any laws, listing requirements, or governmental
regulations (including, without limitation, the provisions of Section 423 of the Code and the regulations and other interpretive guidance issued thereunder relating to Employee Stock Purchase Plans with respect to any 423 Component) including
without limitation any such regulations or other guidance that may be issued or amended after the date the Plan is adopted by the Board, or (iii) without the consent of a person to whom such Purchase Rights were granted, as necessary to obtain
or maintain favorable tax, listing, or regulatory treatment. Notwithstanding anything in the Plan or any Offering Document to the contrary, the Board will be entitled to: (i) establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars; (ii) permit Contributions in excess of the amount designated by a Participant in order to adjust for mistakes in the Company’s processing of properly completed Contribution elections; (iii) establish
reasonable waiting and adjustment periods and/or accounting and crediting procedures to ensure that amounts applied toward the purchase of Common Stock for each Participant properly correspond with amounts withheld from the Participant’s
Contributions; (iv) amend any outstanding Purchase Rights or clarify any ambiguities regarding the terms of any Offering to enable the Purchase Rights to qualify under and/or comply with Section 423 of the Code with respect to the 423
Component; and (v) establish other limitations or procedures as the Board determines in its sole discretion advisable that are consistent with the Plan. The actions of the Board pursuant to this paragraph will not be considered to alter or
impair any Purchase Rights granted under an Offering as they are part of the initial terms of each Offering and the Purchase Rights granted under each Offering. 

13. TAX QUALIFICATION; TAX WITHHOLDING. 

(a) Although the Company may endeavor to (i) qualify a Purchase Right for special tax treatment under the laws of the United States
or jurisdictions outside of the United States or (ii) avoid adverse tax treatment, the Company makes no representation to that effect and expressly disavows any covenant to maintain special or to avoid unfavorable tax treatment, notwithstanding
anything to the contrary in this Plan. The Company is not limited in its corporate activities without regard to the potential negative tax impact on Participants. 

(b) Each Participant will make arrangements, satisfactory to the Company and any applicable Related Corporation, to enable the Company
or the Related Corporation to fulfill any withholding obligation for Tax-Related Items. Without limitation to the foregoing, in the Company’s sole discretion and subject to Applicable Law, such
withholding obligation may be satisfied in whole or in part by (i) withholding from the Participant’s salary or any other cash amount due to the Participant from the Company or a Related Corporation; (ii) withholding from the proceeds
of the sale of shares of Common Stock acquired under the Plan, either through a voluntary sale or a mandatory sale arranged by the Company; or (iii) any other method deemed acceptable by the Board. 

  
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 14. EFFECTIVE DATE OF PLAN.

 The Plan will become effective immediately prior to and contingent upon the IPO Date. No Purchase Rights will be exercised unless and
until the Plan has been approved by the stockholders of the Company, which approval must be within 12 months before or after the date the Plan is adopted (or if required under Section 12(a) above, materially amended) by the Board. 

15. MISCELLANEOUS PROVISIONS. 

(a) Proceeds from the sale of shares of Common Stock pursuant to Purchase Rights will constitute general funds of the Company. 

(b) A Participant will not be deemed to be the holder of, or to have any of the rights of a holder with respect to, shares of Common
Stock subject to Purchase Rights unless and until the Participant’s shares of Common Stock acquired upon exercise of Purchase Rights are recorded in the books of the Company (or its transfer agent). 

(c) The Plan and Offering do not constitute an employment contract. Nothing in the Plan or in the Offering will in any way alter the at
will nature of a Participant’s employment, if applicable, or be deemed to create in any way whatsoever any obligation on the part of any Participant to continue in the employ of the Company or a Related Corporation, or on the part of the
Company or a Related Corporation to continue the employment of a Participant. 
 (d) The provisions of the Plan will be governed by
the laws of the State of Delaware without resort to that state’s conflicts of laws rules. 
 (e) If any particular provision of
the Plan is found to be invalid or otherwise unenforceable, such provision will not affect the other provisions of the Plan, but the Plan will be construed in all respects as if such invalid provision were omitted. 

(f) If any provision of the Plan does not comply with Applicable Law, such provision shall be amended and construed in such a manner as
to comply with Applicable Law. 
 (g) The Company may deliver any forms relating to participation by electronic means and request a
Participant’s forms by electronic means. Upon enrollment, the Participant consents to receive documents by electronic delivery and agrees to participate in the Plan through any on-line or electronic
system established and maintained by the Company or another third party designated by the Company. 
 16. DEFINITIONS. 

As used in the Plan, the following definitions will apply to the capitalized terms indicated below: 

(a) “423 Component” means the part of the Plan, which excludes
the Non-Section 423 Component, pursuant to which Purchase Rights that satisfy the requirements for an Employee Stock Purchase Plan may be granted to Eligible Employees. 

(b) “Applicable Law” means any applicable securities, federal, state, foreign, material local or municipal, or
other law, statute, constitution, principle of common law, resolution, ordinance, code, edict, decree, rule, listing rule, regulation, judicial decision, ruling, or requirement issued, enacted, adopted, promulgated, implemented, or otherwise put
into effect by or under the authority of any Governmental Body (or under the authority of the NASDAQ Stock Market or the Financial Industry Regulatory Authority). 

(c) “Board” means the Board of Directors of the Company. 

  
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 (d) “Capitalization Adjustment” means any change that is made
in, or other events that occur with respect to, the Common Stock subject to the Plan or subject to any Purchase Right after the date the Plan is adopted by the Board without the receipt of consideration by the Company through merger, consolidation,
reorganization, recapitalization, reincorporation, stock dividend, dividend in property other than cash, large nonrecurring cash dividend, stock split, liquidating dividend, combination of shares, exchange of shares, change in corporate structure,
or other similar equity restructuring transaction, as that term is used in Financial Accounting Standards Board Accounting Standards Codification Topic 718 (or any successor thereto). Notwithstanding the foregoing, the conversion of any convertible
securities of the Company will not be treated as a Capitalization Adjustment. 
 (e) “Code” means
the U.S. Internal Revenue Code of 1986, as amended, including any applicable regulations and guidance thereunder. 
 (f)
“Committee” means a committee of one or more members of the Board to whom authority has been delegated by the Board in accordance with Section 2(c). 

(g) “Common Stock” means the Common Stock of the Company. 

(h) “Company” means Caribou Biosciences, Inc., a Delaware corporation. 

(i) “Contributions” means the payroll deductions and other additional payments specifically provided for in the
Offering that a Participant contributes to fund the exercise of a Purchase Right. A Participant may make additional payments into their account if specifically provided for in the Offering, and then only if the Participant has not already had the
maximum permitted amount withheld during the Offering through payroll deductions. 
 (j)
“Director” means a member of the Board. 
 (k) “Eligible
Employee” means an Employee who meets the requirements set forth in the document(s) governing the Offering for eligibility to participate in the Offering, provided that such Employee also meets the requirements for
eligibility to participate set forth in the Plan. 
 (l) “Employee” means any person, including
an Officer or Director, who is “employed” for purposes of Section 423(b)(4) of the Code by the Company or a Related Corporation. However, service solely as a Director, or payment of a fee for such services, will not cause a Director
to be considered an “Employee” for purposes of the Plan. 
 (m) “Employee Stock Purchase
Plan” means a plan that grants Purchase Rights intended to be options issued under an “employee stock purchase plan,” as that term is defined in Section 423(b) of the Code. 

(n) “Exchange Act” means the U.S. Securities Exchange Act of 1934, as amended and the rules and
regulations promulgated thereunder. 
 (o) “Fair Market Value” means, as of any date, the value of the Common
Stock determined as follows: 
 (i) If the Common Stock is listed on any established stock exchange or traded on any established
market, the Fair Market Value of a share of Common Stock will be the closing sales price for such stock as quoted on such exchange or market (or the exchange or market with the greatest volume of trading in the Common Stock) on the date of
determination, as reported in such source as the Board deems reliable. Unless otherwise provided by the Board, if there is no closing sales price for the Common Stock on the date of determination, then the Fair Market Value will be the closing sales
price on the last preceding date for which such quotation exists. 
 (ii) In the absence of such markets for the Common Stock, the
Fair Market Value will be determined by the Board in good faith in compliance with Applicable Laws and regulations and in a manner that complies with Section 409A of the Code. 

  
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 (iii) Notwithstanding the foregoing, for any Offering that commences on the IPO Date,
the Fair Market Value of the shares of Common Stock on the Offering Date will be the price per share at which shares are first sold to the public in the Company’s initial public offering as specified in the final prospectus for that initial
public offering. 
 (p) “Governmental Body” means any: (a) nation, state,
commonwealth, province, territory, county, municipality, district, or other jurisdiction of any nature; (b) federal, state, local, municipal, foreign, or other government; (c) governmental or regulatory body, or quasi-governmental body of
any nature (including any governmental division, department, administrative agency or bureau, commission, authority, instrumentality, official, ministry, fund, foundation, center, organization, unit, body, or entity and any court or other tribunal,
and for the avoidance of doubt, any tax authority or other body exercising similar powers or authority; or (d) self-regulatory organization (including the NASDAQ Stock Market and the Financial Industry Regulatory Authority). 

(q) “IPO Date” means the date of the underwriting agreement between the Company and the
underwriters managing the initial public offering of the Common Stock, pursuant to which the Common Stock is priced for the initial public offering. 

(r) “Non-Section 423 Component” means
the part of the Plan, which excludes the 423 Component, pursuant to which Purchase Rights that are not intended to satisfy the requirements for an Employee Stock Purchase Plan may be granted to Eligible Employees. 

(s) “Offering” means the grant to Eligible Employees of Purchase Rights, with the exercise of those
Purchase Rights automatically occurring at the end of one or more Purchase Periods. The terms and conditions of an Offering will generally be set forth in the “Offering Document” approved by the Board for that Offering. 

(t) “Offering Date” means a date selected by the Board for an Offering to commence. 

(u) “Officer” means a person who is an officer of the Company or a Related Corporation
within the meaning of Section 16 of the Exchange Act. 
 (v) “Participant” means an Eligible
Employee who holds an outstanding Purchase Right. 
 (w) “Plan” means this Caribou Biosciences,
Inc. 2021 Employee Stock Purchase Plan, as amended from time to time, including both the 423 Component and the Non-Section 423 Component. 

(x) “Purchase Date” means one or more dates during an Offering selected by the Board on which
Purchase Rights will be exercised and on which purchases of shares of Common Stock will be carried out in accordance with such Offering. 

(y) “Purchase Period” means a period of time specified within an Offering, generally beginning on the Offering
Date or on the first Trading Day following a Purchase Date, and ending on a Purchase Date. An Offering may consist of one or more Purchase Periods. 

(z) “Purchase Right” means an option to purchase shares of Common Stock granted pursuant to the
Plan. 
 (aa) “Related Corporation” means any “parent corporation” or “subsidiary
corporation” of the Company whether now or subsequently established, as those terms are defined in Sections 424(e) and (f), respectively, of the Code. 

(bb) “Securities Act” means the U.S. Securities Act of 1933, as amended. 

(cc) “Tax-Related Items” means any
income tax, social insurance, payroll tax, fringe benefit tax, payment on account, or other tax-related items arising out of or in relation to a Participant’s participation in the Plan,
including, but not limited to, the exercise of a Purchase Right and the receipt of shares of Common Stock or the sale or other disposition of shares of Common Stock acquired under the Plan. 

  
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 (dd) “Trading Day” means any day on
which the exchange(s) or market(s) on which shares of Common Stock are listed, including but not limited to the NYSE, Nasdaq Global Select Market, the Nasdaq Global Market, the Nasdaq Capital Market or any successors thereto, is open for trading.


  
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