Document:

EX-10.62

 Exhibit 10.62 

EXECUTION VERSION 
 SECOND
AMENDED AND RESTATED 
 RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT 

THIS SECOND AMENDED AND RESTATED RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT (this
“Agreement”) is made as of March 2, 2021 by and among Caribou Biosciences, Inc. a Delaware corporation (the “Company”), the Investors listed on Schedule A and the Key Holders listed on
Schedule B. 
 WHEREAS, the Company, the Key Holders and certain of the Investors (the “Prior
Investors”) previously entered into an Amended and Restated Right of First Refusal and Co-Sale Agreement, dated as of May 12, 2016 (the “Prior Agreement”), in connection with the
purchase of shares of Series B Preferred Stock of the Company, par value $0.0001 per share (“Series B Preferred Stock”); 

WHEREAS, the Key Holders, the Prior Investors and the Company desire to induce certain of the Investors to purchase shares of Series C
Preferred Stock of the Company, par value $0.0001 per share (“Series C Preferred Stock”), pursuant to the Series C Preferred Stock Purchase Agreement dated as of the date hereof by and among the Company and certain of the Investors
(the “Purchase Agreement”), by amending and restating the Prior Agreement to provide the Investors with the rights and privileges as set forth herein. 

NOW, THEREFORE, the Company, the Key Holders and the Investors (including the Prior Investors) each hereby agree to amend and restate
the Prior Agreement in its entirety as set forth herein, and the parties hereto further agree as follows: 
 1. Definitions. 

1.1 “Affiliate” means, with respect to any specified Investor, any other Investor who, directly or indirectly, controls, is
controlled by, or is under common control with such Investor, including, without limitation, any general partner, limited partner, member, manager, managing member, employee, officer or director of such Investor or any venture capital fund now or
hereafter existing that is controlled by one or more general partners or managing members of, or is under common investment management with or shares the same management company with, such Investor. For purposes of this definition, the term
“control” when used with respect to any Investor shall mean the power to direct the management or policies of such Investor, directly or indirectly, whether through ownership of voting securities, by contract or otherwise, and the terms
“controlling” and “controlled” shall have meanings correlative to the foregoing. 
 1.2 “Capital Stock”
means (a) shares of Common Stock and Preferred Stock (whether now outstanding or hereafter issued in any context), (b) shares of Common Stock issued or issuable upon conversion of Preferred Stock and (c) shares of Common Stock issued or
issuable upon exercise or conversion, as applicable, of stock options, warrants or other convertible securities of the Company, in each case now owned or subsequently acquired by any Key Holder, any Investor, or their respective successors or
permitted transferees or assigns. For purposes of the number of shares of Capital Stock held by an Investor or Key Holder (or any other calculation based thereon), all shares of Preferred Stock shall be deemed to have been converted into Common
Stock at the then-applicable conversion ratio. 
 1.3 “Change of Control” means a
transaction or series of related transactions in which a person, or a group of related persons, acquires from stockholders of the Company shares representing more than fifty percent (50%) of the outstanding voting power of the Company. 

1.4 “Common Stock” means shares of Common Stock of the Company, par value $0.0001 per share. 

1.5 “Company Notice” means written notice from the Company notifying the selling Key Holders that the Company intends to
exercise its Right of First Refusal as to some or all of the Transfer Stock with respect to any Proposed Key Holder Transfer. 

 1.6 “Deemed Liquidation Event” has the meaning ascribed thereto in the
Restated Certificate. 
 1.7 “Investor Notice” means written notice from an Investor notifying the Company and the selling
Key Holder that such Investor intends to exercise its Secondary Refusal Right as to a portion of the Transfer Stock with respect to any Proposed Key Holder Transfer. 

1.8 “Investors” means the Persons named on Schedule A hereto, each Person to whom the rights of an
Investor are assigned pursuant to Section 6.9, each Person who hereafter becomes a signatory to this Agreement pursuant to Section 6.11 and any one of them, as the context may require. 

1.9 “Key Holders” means the Persons named on Schedule B hereto, each Person to whom the rights of a
Key Holder are assigned pursuant to Section 3.1, each Person who hereafter becomes a signatory to this Agreement pursuant to Section 6.9 or 6.17 and any one of them, as the context may
require. 
 1.10 “Preferred Stock” means, collectively, all shares of Series A Preferred Stock, Series A-1 Preferred Stock, Series B Preferred Stock and Series C Preferred Stock. 
 1.11 “Proposed Key
Holder Transfer” means any assignment, sale, offer to sell, pledge, mortgage, hypothecation, encumbrance, disposition of or any other like transfer or encumbering of any Transfer Stock (or any interest therein) proposed by any of the Key
Holders. 
 1.12 “Proposed Transfer Notice” means written notice from a Key Holder setting forth the terms and conditions
of a Proposed Key Holder Transfer. 
 1.13 “Prospective Transferee” means any Person to whom a Key Holder proposes to make
a Proposed Key Holder Transfer. 
 1.14 “Restated Certificate” means the Company’s Fourth Amended and Restated
Certificate of Incorporation, as amended from time to time. 
 1.15 “Right of
Co-Sale” means the right, but not an obligation, of an Investor to participate in a Proposed Key Holder Transfer on the terms and conditions specified in the Proposed Transfer Notice. 

1.16 “Right of First Refusal” means the right, but not an obligation, of the Company, or its permitted transferees or
assigns, to purchase some or all of the Transfer Stock with respect to a Proposed Key Holder Transfer, on the terms and conditions specified in the Proposed Transfer Notice. 

1.17 “Secondary Notice” means written notice from the Company notifying the Investors and the selling Key Holder that the
Company does not intend to exercise its Right of First Refusal as to all shares of Transfer Stock with respect to any Proposed Key Holder Transfer. 

1.18 “Secondary Refusal Right” means the right, but not an obligation, of each Investor to purchase up to its pro rata
portion (based upon the total number of shares of Capital Stock then held by all Investors) of any Transfer Stock not purchased pursuant to the Right of First Refusal, on the terms and conditions specified in the Proposed Transfer Notice. 

1.19 “Series A Preferred Stock” means the Company’s Series A Preferred Stock, par value $0.0001 per share. 

1.20 “Series A-1 Preferred Stock” means the Company’s Series A-1 Preferred Stock, par value $0.0001 per share 
 1.21 “SPAC Transaction”
means any transaction or series of related transactions in which the Company’s outstanding shares of capital stock are exchanged for or otherwise converted into securities that are 

  
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publicly listed on a securities exchange (the “Public Shares”), including through a merger, acquisition, business combination or similar transaction, in each case with a vehicle
commonly known as a special purpose acquisition company ( a “SPAC”). 
 1.22 “Transfer Stock” means shares
of Capital Stock owned by a Key Holder, or issued to a Key Holder after the date hereof (including, without limitation, in connection with any stock split, stock dividend, recapitalization, reorganization, or the like), but does not include any
shares of Preferred Stock or Common Stock issued or issuable upon conversion of Preferred Stock. 
 1.23 “Undersubscription
Notice” means written notice from an Investor notifying the Company and the selling Key Holder that such Investor intends to exercise its option to purchase all or any portion of the Transfer Stock not purchased pursuant to the Right of
First Refusal or the Secondary Refusal Right. 
 2. Agreement Among the Company, the Investors and the Key Holders. 

2.1 Right of First Refusal. 

(a) Grant. Subject to the terms of Section 3 below, each Key Holder hereby unconditionally and irrevocably
grants to the Company a Right of First Refusal to purchase all or any portion of Transfer Stock that such Key Holder may propose to transfer in a Proposed Key Holder Transfer, at the same price and on the same terms and conditions as those offered
to the Prospective Transferee. 
 (b) Notice. Each Key Holder proposing to make a Proposed Key Holder Transfer must deliver a
Proposed Transfer Notice to the Company and each Investor not later than thirty (30) days prior to the consummation of such Proposed Key Holder Transfer. Such Proposed Transfer Notice shall contain the material terms and conditions (including
price and form of consideration) of the Proposed Key Holder Transfer and the identity of the Prospective Transferee (and a description of such Key Holder’s relationship to or affiliation with the Prospective Transferee). To exercise its Right
of First Refusal under this Section 2, the Company must deliver a Company Notice to the selling Key Holder within twenty (20) days after delivery of the Proposed Transfer Notice. In the event of a conflict between this
Agreement and any other agreement that may have been entered into by a Key Holder with the Company that contains a preexisting right of first refusal, the Company and the Key Holder acknowledge and agree that the terms of this Agreement shall
control and the preexisting right of first refusal shall be deemed satisfied by compliance with Section 2.1(a) and this Section 2.1(b). 

(c) Grant of Secondary Refusal Right to Investors. Subject to the terms of Section 3 below, each Key Holder
hereby unconditionally and irrevocably grants to the Investors a Secondary Refusal Right to purchase all or any portion of the Transfer Stock not purchased by the Company pursuant to the Right of First Refusal described in
Section 2.1(b) above, as provided in this Section 2.1(c). If the Company does not intend to exercise its Right of First Refusal with respect to all Transfer Stock subject to a Proposed Key Holder
Transfer, the Company must deliver a Secondary Notice to the selling Key Holder and to each Investor to that effect no later than twenty (20) days after the selling Key Holder delivers the Proposed Transfer Notice to the Company. To exercise
its Secondary Refusal Right, an Investor must deliver an Investor Notice to the selling Key Holder and the Company within ten (10) days after the Company’s deadline for its delivery of the Secondary Notice as provided in the preceding
sentence. 
 (d) Undersubscription of Transfer Stock. If options to purchase have been exercised by the Company and the Investors
with respect to some but not all of the Transfer Stock by the end of the 10-day period specified in the last sentence of Section 2.1(c) (the “Investor Notice
Period”), then the Company shall, immediately after the expiration of the Investor Notice Period, send written notice (the “Company Undersubscription Notice”) to those Investors who fully exercised their Secondary Refusal
Right within the Investor Notice Period (the “Exercising Investors”). Each Exercising Investor shall, subject to the provisions of this Section 2.1(d), have an additional option to purchase all or any part
of the balance of any such remaining unsubscribed shares of Transfer Stock on the terms and conditions set forth in the Proposed Transfer Notice. To exercise such option, an Exercising Investor must deliver an Undersubscription Notice to the selling
Key Holder and the Company within ten (10) days after the expiration of the Investor Notice Period. In the event there are two (2) or 

  
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more such Exercising Investors that choose to exercise the last-mentioned option for a total number of remaining shares in excess of the number available, the remaining shares available for
purchase under this Section 2.1(d) shall be allocated to such Exercising Investors pro rata based on the number of shares of Transfer Stock such Exercising Investors have elected to purchase pursuant to the Secondary
Refusal Right (without giving effect to any shares of Transfer Stock that any such Exercising Investor has elected to purchase pursuant to the Company Undersubscription Notice). If the options to purchase the remaining shares are exercised in full
by the Exercising Investors, the Company shall immediately notify all of the Exercising Investors and the selling Key Holder of that fact. 

(e) Consideration; Closing. If the consideration proposed to be paid for the Transfer Stock is in property, services or other non-cash consideration, the fair market value of the consideration shall be as determined in good faith by the Company’s Board of Directors (the “Board of Directors”) and as set forth in the
Company Notice. If the Company or any Investor cannot for any reason pay for the Transfer Stock in the same form of non-cash consideration, the Company or such Investor may pay the cash value equivalent
thereof, as determined in good faith by the Board of Directors and as set forth in the Company Notice. The closing of the purchase of Transfer Stock by the Company and the Investors shall take place, and all payments from the Company and the
Investors shall have been delivered to the selling Key Holder, by the later of (i) the date specified in the Proposed Transfer Notice as the intended date of the Proposed Key Holder Transfer and (ii) forty-five (45) days after
delivery of the Proposed Transfer Notice. 
 2.2 Right of Co-Sale. 

(a) Exercise of Right. If any Transfer Stock subject to a Proposed Key Holder Transfer is not purchased pursuant to
Section 2.1 above and thereafter is to be sold to a Prospective Transferee, each respective Investor may elect to exercise its Right of Co-Sale and participate on a pro rata basis in
the Proposed Key Holder Transfer as set forth in Section 2.2(b) below and, subject to Section 2.2(d), otherwise on the same terms and conditions specified in the Proposed Transfer Notice. Each
Investor who desires to exercise its Right of Co-Sale (each, a “Participating Investor”) must give the selling Key Holder written notice to that effect within fifteen (15) days after the
deadline for delivery of the Secondary Notice described above, and upon giving such notice such Participating Investor shall be deemed to have effectively exercised the Right of Co-Sale. 

(b) Shares Includable. Each Participating Investor may include in the Proposed Key Holder Transfer all or any part of such
Participating Investor’s Capital Stock equal to the product obtained by multiplying (i) the aggregate number of shares of Transfer Stock subject to the Proposed Key Holder Transfer (excluding shares purchased by the Company or the
Participating Investors pursuant to the Right of First Refusal or the Secondary Refusal Right) by (ii) a fraction, the numerator of which is the number of shares of Capital Stock owned by such Participating Investor immediately before
consummation of the Proposed Key Holder Transfer (excluding any shares that such Investor has agreed to purchase pursuant to the Secondary Refusal Right) and the denominator of which is the total number of shares of Capital Stock owned, in the
aggregate, by all Participating Investors immediately prior to the consummation of the Proposed Key Holder Transfer (excluding any shares that all Participating Investors have collectively agreed to purchase pursuant to the Secondary Refusal Right),
plus the number of shares of Transfer Stock held by the selling Key Holder. To the extent one or more of the Participating Investors exercise such right of participation in accordance with the terms and conditions set forth herein, the number of
shares of Transfer Stock that the selling Key Holder may sell in the Proposed Key Holder Transfer shall be correspondingly reduced. 
 (c)
Purchase and Sale Agreement. The Participating Investors and the selling Key Holder agree that the terms and conditions of any Proposed Key Holder Transfer in accordance with Section 2.2 will be memorialized in, and
governed by, a written purchase and sale agreement with the Prospective Transferee (the “Purchase and Sale Agreement”) with customary terms and provisions for such a transaction, and the Participating Investors and the selling Key
Holder further covenant and agree to enter into such Purchase and Sale Agreement as a condition precedent to any sale or other transfer in accordance with this Section 2.2. 

  
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 (d) Allocation of Consideration. 

(i) Subject to Section 2.2(d)(ii), the aggregate consideration payable to the Participating Investors and the
selling Key Holder shall be allocated based on the number of shares of Capital Stock sold to the Prospective Transferee by each Participating Investor and the selling Key Holder as provided in Section 2.2(b),
provided, that if a Participating Investor wishes to sell Preferred Stock, the price set forth in the Proposed Transfer Notice shall be appropriately adjusted based on the conversion ratio of the Preferred Stock into Common Stock. 

(ii) In the event that the Proposed Key Holder Transfer constitutes a Change of Control, the terms of the Purchase and Sale Agreement shall
provide that the aggregate consideration from such transfer shall be allocated to the Participating Investors and the selling Key Holder in accordance with Sections 2.1 and 2.2 of Article FOURTH, Part (B) of the Restated Certificate as if
(A) such transfer were a Deemed Liquidation Event (as defined in the Restated Certificate), and (B) the Capital Stock sold in accordance with the Purchase and Sale Agreement were the only Capital Stock outstanding. In the event that a
portion of the aggregate consideration payable to the Participating Investor(s) and selling Key Holder is placed into escrow and/or is payable only upon satisfaction of contingencies, the Purchase and Sale Agreement shall provide that (x) the
portion of such consideration that is not placed in escrow and is not subject to contingencies (the “Initial Consideration”) shall be allocated in accordance with Sections 2.1 and 2.2 of Article FOURTH, Part (B) of the Restated
Certificate as if the Initial Consideration were the only consideration payable in connection with such transfer, and (y) any additional consideration which becomes payable to the Participating Investor(s) and selling Key Holder upon release
from escrow or satisfaction of such contingencies shall be allocated in accordance with Sections 2.1 and 2.2 of Article FOURTH, Part (B) of the Restated Certificate after taking into account the previous payment of the Initial Consideration as
part of the same transfer. 
 (e) Purchase by Selling Key Holder; Deliveries. Notwithstanding
Section 2.2(c) above, if any Prospective Transferee or Transferees refuse(s) to purchase securities subject to the Right of Co-Sale from any Participating Investor or Investors or
upon the failure to negotiate in good faith a Purchase and Sale Agreement reasonably satisfactory to the Participating Investors, no Key Holder may sell any Transfer Stock to such Prospective Transferee or Transferees unless and until,
simultaneously with such sale, such Key Holder purchases all securities subject to the Right of Co-Sale from such Participating Investor or Investors on the same terms and conditions (including the proposed
purchase price) as set forth in the Proposed Transfer Notice and as provided in Section 2.2(d)(i); provided, however, if such sale constitutes a Change of Control, the portion of the aggregate
consideration paid by the selling Key Holder to such Participating Investor or Investors shall be made in accordance with the first sentence of Section 2.2(d)(ii). In connection with such purchase by the selling Key Holder,
such Participating Investor or Investors shall deliver to the selling Key Holder a stock certificate or certificates, properly endorsed for transfer, representing the Capital Stock being purchased by the selling Key Holder. Each such stock
certificate delivered to the selling Key Holder will be transferred to the Prospective Transferee against payment therefor in consummation of the sale of the Transfer Stock pursuant to the terms and conditions specified in the Proposed Transfer
Notice, and the selling Key Holder shall concurrently therewith remit or direct payment to each such Participating Investor the portion of the aggregate consideration to which each such Participating Investor is entitled by reason of its
participation in such sale as provided in this Section 2.2(e). 
 (f) Additional Compliance. If any
Proposed Key Holder Transfer is not consummated within sixty (60) days after receipt of the Proposed Transfer Notice by the Company, the Key Holders proposing the Proposed Key Holder Transfer may not sell any Transfer Stock unless they first
comply in full with each provision of this Section 2. The exercise or election not to exercise any right by any Investor hereunder shall not adversely affect its right to participate in any other sales of Transfer Stock
subject to this Section 2.2. 
 2.3 Effect of Failure to Comply. 

(a) Transfer Void; Equitable Relief. Any Proposed Key Holder Transfer not made in compliance with the requirements of this Agreement
shall be null and void ab initio, shall not be recorded on the books of the Company or its transfer agent and shall not be recognized by the Company. Each party hereto acknowledges and agrees that any breach of this Agreement would result in
substantial harm to the other parties hereto for which monetary damages alone could not adequately compensate. Therefore, the parties hereto unconditionally and irrevocably agree that any non-breaching party
hereto shall be entitled to seek protective orders, 

  
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injunctive relief and other remedies available at law or in equity (including, without limitation, seeking specific performance or the rescission of purchases, sales and other transfers of
Transfer Stock not made in strict compliance with this Agreement). 
 (b) Violation of First Refusal Right. If any Key Holder
becomes obligated to sell any Transfer Stock to the Company or any Investor under this Agreement and fails to deliver such Transfer Stock in accordance with the terms of this Agreement, the Company and/or such Investor may, at its option, in
addition to all other remedies it may have, send to such Key Holder the purchase price for such Transfer Stock as is herein specified and transfer to the name of the Company or such Investor (or request that the Company effect such transfer in the
name of an Investor) on the Company’s books the certificate or certificates representing the Transfer Stock to be sold. 
 (c)
Violation of Co-Sale Right. If any Key Holder purports to sell any Transfer Stock in contravention of the Right of Co-Sale (a “Prohibited
Transfer”), each Investor who desires to exercise its Right of Co-Sale under Section 2.2 may, in addition to such remedies as may be available by law, in equity or hereunder,
require such Key Holder to purchase from such Investor the type and number of shares of Capital Stock that such Investor would have been entitled to sell to the Prospective Transferee under Section 2.2 had the Prohibited
Transfer been effected pursuant to and in compliance with the terms of Section 2.2. The sale will be made on the same terms, including, without limitation, as provided in Section 2.2(d)(i) and the
first sentence of Section 2.2(d)(ii), as applicable, and subject to the same conditions as would have applied had the Key Holder not made the Prohibited Transfer, except that the sale (including, without limitation, the
delivery of the purchase price) must be made within ninety (90) days after the Investor learns of the Prohibited Transfer, as opposed to the timeframe proscribed in Section 2.2. Such Key Holder shall also reimburse
each Investor for any and all reasonable and documented out-of-pocket fees and expenses, including reasonable legal fees and expenses, incurred pursuant to the exercise
or the attempted exercise of the Investor’s rights under Section 2.2. 
 3. Exempt Transfers. 

3.1 Exempted Transfers. Notwithstanding the foregoing or anything to the contrary herein, the provisions of Sections 2.1 and
2.2 shall not apply: (a) in the case of a Key Holder that is an entity, upon a transfer by such Key Holder to its stockholders, members, partners or other equity holders; (b) to a repurchase of Transfer Stock from a Key Holder by
the Company at a price no greater than that originally paid by such Key Holder for such Transfer Stock and pursuant to an agreement containing vesting and/or repurchase provisions approved by a majority of the Board of Directors; or (c) in the
case of a Key Holder that is a natural person, upon a transfer of Transfer Stock by such Key Holder made for bona fide estate planning purposes, either during his or her lifetime or on death by will or intestacy to his or her spouse, child (natural
or adopted), or any other direct lineal descendant of such Key Holder (or his or her spouse) (all of the foregoing collectively referred to as “family members”), or any custodian or trustee of any trust, partnership or limited
liability company solely for the benefit of, or the ownership interests of which are owned wholly by, such Key Holder or any such family members; provided that in the case of clause(s) (a) or (c), the Key Holder shall deliver prior
written notice to the Investors of such gift or transfer and such shares of Transfer Stock shall at all times remain subject to the terms and restrictions set forth in this Agreement and such transferee shall, as a condition to such transfer,
deliver a counterpart signature page to this Agreement as confirmation that such transferee shall be bound by all the terms and conditions of this Agreement as a Key Holder (but only with respect to the securities so transferred to the transferee),
including the obligations of a Key Holder with respect to Proposed Key Holder Transfers of such Transfer Stock pursuant to Section 2; and provided, further, in the case of any transfer pursuant to clause
(a) or (c) above, that such transfer is made pursuant to a transaction in which there is no consideration actually paid for such transfer. 

3.2 Exempted Offerings. Notwithstanding the foregoing or anything to the contrary herein, the provisions of
Section 2 shall not apply to the sale of any Transfer Stock (a) to the public in an offering pursuant to an effective registration statement under the Securities Act of 1933, as amended (a “Public
Offering”) or (b) pursuant to a Deemed Liquidation Event. 
 3.3 Prohibited Transferees. Notwithstanding the foregoing,
no Key Holder shall transfer any Transfer Stock to (a) any entity that, in the determination of the Board of Directors, directly or indirectly competes with the Company; provided, however, that, for purposes of this
Section 3.3, in no event shall the Board of Directors 

  
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determine that Pig Improvement Company UK Limited (“PIC”), Anterra F&A Ventures I Coöperatief U.A. (“Anterra”),
F-Prime Capital Partners Healthcare Fund IV LP (“F-Prime”), Novartis Institutes for BioMedical Research, Inc. (“Novartis”), E. I. du
Pont de Nemours and Company (“DuPont”), PFM Healthcare Master Fund, L.P., Partner Investments, L.P., PFM Healthcare Growth Equity Holdings I, LLC (“PFM”), and its Affiliate funds, Zone III Healthcare Holdings, LLC
(“Farallon”) and its Affiliate funds, Ridgeback Capital Management (“Ridgeback”) and its Affiliate funds, or AbbVie Inc. (“AbbVie”) or AbbVie Manufacturing Management Unlimited Company (as long as
it remains an Affiliate of AbbVie) directly or indirectly competes with the Company or (b) any customer, distributor or supplier of the Company (which, for the avoidance of doubt shall not include AbbVie), if the Company’s Board of
Directors should determine that such transfer would result in such customer, distributor or supplier receiving information that would place the Company at a competitive disadvantage with respect to such customer, distributor or supplier. 

4. Legend. Each certificate representing shares of Transfer Stock held by the Key Holders or issued to any permitted transferee in
connection with a transfer permitted by Section 3.1 hereof shall be endorsed with the following legend: 
 THE
SALE, PLEDGE, HYPOTHECATION OR TRANSFER OF THE SECURITIES REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO, AND IN CERTAIN CASES PROHIBITED BY, THE TERMS AND CONDITIONS OF A CERTAIN RIGHT OF FIRST REFUSAL AND
CO-SALE AGREEMENT BY AND AMONG THE STOCKHOLDER, THE CORPORATION AND CERTAIN OTHER HOLDERS OF STOCK OF THE CORPORATION. COPIES OF SUCH AGREEMENT MAY BE OBTAINED UPON WRITTEN REQUEST TO THE SECRETARY OF THE
CORPORATION. 
 Each Key Holder agrees that the Company may instruct its transfer agent to impose transfer restrictions on the shares represented by
certificates bearing the legend referred to in this Section 4 above to enforce the provisions of this Agreement, and the Company agrees to promptly do so. The legend shall be removed upon termination or expiration of the
restrictions set forth in this Agreement at the request of the holder. 
 5. Lock-Up. 

5.1 Agreement to Lock-Up. 

(a) Each Key Holder hereby agrees that it will not, without the prior written consent of the managing underwriter, during the period
commencing on the date of the final prospectus relating to the Company’s initial public offering (the “IPO”) and ending on the date specified by the Company and the managing underwriter (such period not to exceed one hundred
eighty (180) days, which period may be extended upon the request of the managing underwriter for an additional period of up to fifteen (15) days to accommodate regulatory restrictions on (1) the publication or other
distribution of research reports, and (2) analyst recommendations and opinions, including, but not limited to, the restrictions contained in FINRA Rule 2711(f)(4) or NYSE Rule 472(f)(4), or any successor provisions or amendments thereto)
(a) lend, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any
shares of Capital Stock held immediately before the effective date of the registration statement for the IPO (excluding any shares purchased in connection with or conditioned on the IPO and any securities acquired following the effective date of the
registration statement for the IPO) or (b) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Capital Stock, whether any such transaction described in
clause (a) or (b) above is to be settled by delivery of Capital Stock or other securities, in cash or otherwise. The foregoing provisions of this Section 5.1 shall only apply to the IPO and shall not apply to the
sale of any shares to an underwriter pursuant to an underwriting agreement, or the transfer of any shares to any trust for the direct or indirect benefit of the Key Holder or the immediate family of the Key Holder (provided that the trustee
of the trust agrees to be bound in writing by the restrictions set forth herein and provided, further that any such transfer shall not involve a disposition for value), and shall only be applicable to the Key Holders if all officers
and directors are subject to the same restrictions and the Company uses commercially reasonable efforts to obtain a similar agreement from all holders of more than one percent (1%) of the outstanding Common Stock (after giving effect to the
conversion into 

  
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Common Stock of all outstanding Preferred Stock). The underwriters in connection with the IPO are intended third-party beneficiaries of this
Section 5 and shall have the right, power and authority to enforce the provisions hereof as though they were a party hereto. Each Key Holder further agrees to execute such agreements as may be reasonably requested by the
underwriters in the IPO (or any other registration, as applicable) that are consistent with this Section 5 or that are necessary to give further effect thereto. 

(b) In connection with a SPAC Transaction, each Key Holder agrees to enter into an agreement with the SPAC or the Company to not transfer the
Public Shares received by such Key Holder in connection with the SPAC Transaction (excluding any Public Shares received in exchange for or upon conversion of securities issued in a private placement that is connected to or conditioned on the SPAC
Transaction) pursuant to terms substantially similar to the terms in Section 5.1(a) (modified as appropriate for a SPAC Transaction). 

5.2 Stop Transfer Instructions. In order to enforce the foregoing covenant, the Company may impose stop-transfer instructions with
respect to the shares of Capital Stock of each Key Holder (and transferees and assignees thereof) until the end of such restricted period. 

6. Miscellaneous. 
 6.1
Term. This Agreement shall automatically terminate upon the earliest of (a) immediately prior to the consummation of the Company’s IPO, (b) immediately prior to the consummation of a SPAC Transaction (as defined in the Restated
Certificate), and (c) the consummation of a Deemed Liquidation Event, provided that the provisions of Section 6 will survive any such event. 

6.2 Stock Split. All references to numbers of shares in this Agreement shall be appropriately adjusted to reflect any stock dividend,
split, combination or other recapitalization affecting the Capital Stock occurring after the date of this Agreement. 
 6.3
Ownership. Each Key Holder represents and warrants that such Key Holder is the sole legal and beneficial owner of the shares of Transfer Stock subject to this Agreement and that no other person or entity has any interest in such shares (other
than a community property interest as to which the holder thereof has acknowledged and agreed in writing to the restrictions and obligations hereunder). 

6.4 Dispute Resolution. The parties (a) hereby irrevocably and unconditionally submit to the jurisdiction of the state courts of
Delaware and to the jurisdiction of the United States District Court for the District of Delaware for the purpose of any suit, action or other proceeding arising out of or based upon this Agreement, (b) agree not to commence any suit, action or
other proceeding arising out of or based upon this Agreement except in the state courts of Delaware or the United States District Court for the District of Delaware, and (c) hereby waive, and agree not to assert, by way of motion, as a defense,
or otherwise, in any such suit, action or proceeding, any claim that it is not subject personally to the jurisdiction of the above-named courts, that its property is exempt or immune from attachment or execution, that the suit, action or proceeding
is brought in an inconvenient forum, that the venue of the suit, action or proceeding is improper or that this Agreement or the subject matter hereof may not be enforced in or by such court. 

WAIVER OF JURY TRIAL: EACH PARTY HEREBY WAIVES ITS RIGHTS TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS AGREEMENT, THE
OTHER TRANSACTION DOCUMENTS, THE SECURITIES OR THE SUBJECT MATTER HEREOF OR THEREOF. THE SCOPE OF THIS WAIVER IS INTENDED TO BE ALL-ENCOMPASSING OF ANY AND ALL DISPUTES THAT MAY BE FILED IN ANY COURT AND THAT
RELATE TO THE SUBJECT MATTER OF THIS TRANSACTION, INCLUDING, WITHOUT LIMITATION, CONTRACT CLAIMS, TORT CLAIMS (INCLUDING NEGLIGENCE), BREACH OF DUTY CLAIMS, AND ALL OTHER COMMON LAW AND STATUTORY CLAIMS. THIS SECTION HAS BEEN FULLY DISCUSSED BY EACH
OF THE PARTIES HERETO AND THESE PROVISIONS WILL NOT BE SUBJECT TO ANY EXCEPTIONS. EACH PARTY HERETO HEREBY FURTHER WARRANTS AND REPRESENTS THAT SUCH PARTY HAS REVIEWED THIS WAIVER WITH ITS LEGAL COUNSEL, AND THAT SUCH PARTY KNOWINGLY AND VOLUNTARILY
WAIVES ITS JURY TRIAL RIGHTS FOLLOWING CONSULTATION WITH LEGAL COUNSEL. 

  
 8 

 6.5 Notices. 

(a) All notices and other communications given or made pursuant to this Agreement shall be in writing and shall be deemed effectively given
upon the earlier of actual receipt or: (a) personal delivery to the party to be notified, (b) when sent, if sent by facsimile or email (with confirmation of receipt) during normal business hours of the recipient, and if not sent during
normal business hours, then on the recipient’s next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) business day after deposit with a
nationally recognized overnight courier, freight prepaid, specifying next business day delivery, with written verification of receipt. All communications shall be sent to the respective parties at their address as set forth on Schedule A or
Schedule B hereof, as the case may be, or to such address, email or facsimile number as subsequently modified by written notice given in accordance with this Section 6.5. If notice is given to the Company, it shall
be sent to Caribou Biosciences, Inc., 2929 7th Street, Suite 105, Berkeley, CA 94710, email legalnotices@cariboubio.com, Attention: Chief Legal Officer; and a copy (which shall not constitute notice) shall also be sent to Reed Smith LLP, 1901 Avenue
of the Stars, Suite 700, Los Angeles, California 90067, email amukhey@reedsmith.com, Attention: Ashok Mukhey, Esq., and if notice is given to Investors, a copy shall also be given to such counsel as may appear with such Investors’ address on
Schedule A hereto. 
 (b) Each Investor and Key Holder consents to the delivery of any stockholder notice pursuant to the Delaware
General Corporation Law (the “DGCL”), as amended or superseded from time to time, or under this Agreement by electronic transmission pursuant to Section 232 of the DGCL (or any successor thereto) at the email address set forth
below such Investor’s or Key Holder’s name on the Schedules hereto, as updated from time to time by notice to the Company or as on the books of the Company. Each Investor and Key Holder agrees to promptly notify the Company of any change
in its email address, and the failure to do so shall not affect the foregoing. 
 6.6 Entire Agreement. This Agreement (including the
Exhibits and Schedules hereto) constitutes the full and entire understanding and agreement between the parties with respect to the subject matter hereof, and any other written or oral agreement relating to the subject matter hereof existing between
the parties are expressly canceled. 
 6.7 Delays or Omissions. No delay or omission to exercise any right, power or remedy accruing
to any party under this Agreement, upon any breach or default of any other party under this Agreement, shall impair any such right, power or remedy of such non-breaching or
non-defaulting party nor shall it be construed to be a waiver of any such breach or default, or an acquiescence therein, or of or in any similar breach or default thereafter occurring; nor shall any waiver of
any single breach or default be deemed a waiver of any other breach or default theretofore or thereafter occurring. Any waiver, permit, consent or approval of any kind or character on the part of any party of any breach or default under this
Agreement, or any waiver on the part of any party of any provisions or conditions of this Agreement, must be in writing and shall be effective only to the extent specifically set forth in such writing. All remedies, either under this Agreement or by
law or otherwise afforded to any party, shall be cumulative and not alternative. 
 6.8 Amendment; Waiver and Termination. This
Agreement may be amended, modified or terminated (other than pursuant to Section 6.1 above) and the observance of any term hereof may be waived (either generally or in a particular instance and either retroactively or
prospectively) only by a written instrument executed by (a) the Company, (b) the Key Holders holding at least a majority of the shares of Transfer Stock then held by all of the Key Holders who are then employed by Company and (c) the
holders of at least a majority of the shares of Common Stock issued or issuable upon conversion of the then outstanding shares of Preferred Stock held by the Investors (voting as a single class and on an
as-converted to Common Stock basis). Any amendment, modification, termination or waiver so effected shall be binding upon the Company, the Investors, the Key Holders and all of their respective successors and
permitted assigns whether or not such party, assignee or other shareholder entered into or approved such amendment, modification, termination or waiver. Notwithstanding the foregoing, (i) this Agreement may not be amended, modified or
terminated and the observance of any term hereunder may not be waived with 

  
 9 

 
respect to any Investor or Key Holder without the written consent of such Investor or Key Holder unless such amendment, modification, termination or waiver applies to all Investors and Key
Holders, respectively, in the same fashion, (ii) the consent of the Key Holders shall not be required for any amendment, modification, termination or waiver if such amendment, modification, termination or waiver does not apply to the Key
Holders, (iii) Schedule A hereto may be amended by the Company from time to time in accordance with the Purchase Agreement to add information regarding Additional Purchasers (as defined in the Purchase Agreement) without the consent of
the other parties hereto, (iv) Section 3.3 of this Agreement may not be amended, modified, or terminated, and the observance of any term of Section 3.3 may not be waived, without the written
consent of PIC, Anterra, F-Prime, Novartis, DuPont, PFM, Farallon, Ridgeback, or AbbVie to the extent such amendment, modification, termination, or waiver affects such party,
(v) Section 2.2(d)(ii) of this Agreement may not be amended, modified, or terminated, and the observance of any term of Section 2.2(d)(ii) may not be waived, without the written consent of
(A) the holders of a majority of the outstanding Series B Preferred Stock, voting or consenting together as a single class, and (B) the holders of at least two-thirds (2/3rds) of the outstanding
Series C Preferred Stock, voting or consenting together as a single class, and (vi) Schedule B hereto may be amended by the Company from time to time in accordance with Section 6.17 below to add information
regarding additional Key Holders without the consent of the other parties hereto. The Company shall give prompt written notice of any amendment, modification or termination hereof or waiver hereunder to any party hereto that did not consent in
writing to such amendment, modification, termination or waiver. No waivers of or exceptions to any term, condition or provision of this Agreement, in any one or more instances, shall be deemed to be, or construed as, a further or continuing waiver
of any such term, condition or provision. 
 6.9 Assignment of Rights. 

(a) The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the respective successors and permitted
assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and permitted assigns any rights, remedies, obligations, or liabilities
under or by reason of this Agreement, except as expressly provided in this Agreement. 
 (b) Any successor or permitted assignee of any Key
Holder, including any Prospective Transferee who purchases shares of Transfer Stock in accordance with the terms hereof, shall deliver to the Company and the Investors, as a condition to any transfer or assignment, a counterpart signature page
hereto pursuant to which such successor or permitted assignee shall confirm their agreement to be subject to and bound by all of the provisions set forth in this Agreement that were applicable to the predecessor or assignor of such successor or
permitted assignee. 
 (c) The rights of the Investors hereunder are not assignable without the Company’s written consent (which shall
not be unreasonably withheld, delayed or conditioned), except (i) by an Investor to any Affiliate or (ii) to an assignee or transferee who acquires at least 100,000 shares of Capital Stock (as adjusted for any stock combination, stock
split, stock dividend, recapitalization or other similar transaction), it being acknowledged and agreed that any such assignment, including an assignment contemplated by the preceding clauses (i) or (ii) shall be subject to and conditioned upon
any such assignee’s delivery to the Company and the other Investors of a counterpart signature page hereto pursuant to which such assignee shall confirm their agreement to be subject to and bound by all of the provisions set forth in this
Agreement that were applicable to the assignor of such assignee. 
 (d) Except in connection with an assignment by the Company by operation
of law to an acquirer or successor of the Company, the rights and obligations of the Company hereunder may not be assigned under any circumstances. 

6.10 Severability. The invalidity or unenforceability of any provision hereof shall in no way affect the validity or enforceability of
any other provision. 
 6.11 Additional Investors. Notwithstanding anything to the contrary contained herein, if the Company issues
additional shares of Series C Preferred Stock pursuant to the Purchase Agreement after the date hereof, any purchaser of such shares of Series C Preferred Stock may become a party to this Agreement by executing and delivering an additional
counterpart signature page to this Agreement and thereafter shall be deemed an “Investor” for all purposes hereunder. 

  
 10 

 6.12 Governing Law. This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware, regardless of the laws that might otherwise govern under applicable principles of conflicts of law. 

6.13 Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered
in construing or interpreting this Agreement. 
 6.14 Counterparts; Electronic Transmission. This Agreement may be executed in two
(2) or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Counterparts may be delivered via facsimile, electronic mail (including pdf or any electronic signature
complying with the U.S. federal ESIGN Act of 2000, e.g., www.docusign.com) or other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes. 

6.15 Aggregation of Stock. All shares of Capital Stock held or acquired by Affiliated entities or persons shall be aggregated together
for the purpose of determining the availability of any rights under this Agreement and such Affiliated persons may apportion such rights as among themselves in any manner they deem appropriate. 

6.16 Specific Performance. In addition to any and all other remedies that may be available at law in the event of any breach of this
Agreement, each Investor shall be entitled to specific performance of the agreements and obligations of the Company and the Key Holders hereunder and to such other injunction or other equitable relief as may be granted by a court of competent
jurisdiction. 
 6.17 Additional Key Holders. In the event that after the date of this Agreement, the Company issues shares of Common
Stock to any employee or consultant, which shares would collectively constitute with respect to such employee or consultant (taking into account all shares of Common stock, options and other purchase rights held by such employee or consultant) one
percent (1%) or more of the Company’s then outstanding Common Stock (treating for this purpose all shares of Common Stock issuable upon exercise of or conversion of outstanding options, warrants or convertible securities, as if exercised or
converted), the Company shall, as a condition to such issuance, cause such employee or consultant to execute a counterpart signature page hereto as a Key Holder, and such person shall thereby be bound by, and subject to, all the terms and provisions
of this Agreement applicable to a Key Holder. 
 6.18 Consent of Spouse. If any Key Holder is married and domiciled in a community
property state on the date of this Agreement, such Key Holder’s spouse shall execute and deliver to the Company a Consent of Spouse in the form of Exhibit A hereto (“Consent of Spouse”), effective on the date hereof.
Notwithstanding the execution and delivery thereof, such consent shall not be deemed to confer or convey to the spouse any rights in such Key Holder’s shares of Transfer Stock that do not otherwise exist by operation of law or the agreement of
the parties. If any Key Holder should marry or remarry and be domiciled in a community property state subsequent to the date of this Agreement, such Key Holder shall within thirty (30) days thereafter obtain his/her new spouse’s
acknowledgement of and consent to the existence and binding effect of all restrictions contained in this Agreement by causing such spouse to execute and deliver a Consent of Spouse acknowledging the restrictions and obligations contained in this
Agreement and agreeing and consenting to the same. 
 6.19 Effect on Prior Agreement. Upon the execution and delivery of this
Agreement by the Company, the Key Holders holding a majority in interest of the Transfer Stock and the holders of at least a majority in interest of the Capital Stock held by those Investors who are party to the Prior Agreement (measured before
giving effect to any purchase of shares of Series C Preferred Stock by such Investors), the Prior Agreement automatically shall terminate and be of no further force and effect and shall be amended and restated in its entirety as set forth in this
Agreement. 

  
 11 

 6.20 Tekla Funds. A copy of the Declaration of Trust, as amended and restated, for
each of Tekla Healthcare Investors and Tekla Life Sciences Investors (together, the “Tekla Funds”) is on file with the Secretary of State of The Commonwealth of Massachusetts, and notice is hereby given that this Agreement is
executed on behalf of the Tekla Funds by an officer or trustee of the Tekla Funds in his or her capacity as an officer or trustee of the Tekla Funds, and not individually and that the obligations of or arising out of this Agreement are not binding
upon any of the trustees, officers or shareholders individually but are binding only upon the assets and property of each of the respective Tekla Funds. 

[Remainder of Page Intentionally Left Blank] 

  
 12 

 EXECUTION VERSION 

IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of First Refusal and
Co-Sale Agreement as of the date first written above. 
  

			
	COMPANY:
	
	CARIBOU BIOSCIENCES, INC.
		
	By:	 	 /s/ Rachel E. Haurwitz

	Name:	 	 Rachel E. Haurwitz

	Title:	 	 President and Chief Executive Officer

  
 Signature Page to
Second Amended and Restated Right of First Refusal and Co-Sale Agreement 

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	PFM Healthcare Master Fund, L.P.
	By: PFM Health Sciences, LP, its investment advisor
		
	By:	 	 /s/ Yuan DuBord

	Name:	 	 Yuan DuBord

	Title:	 	 CFO

	
	Partner Investments, L.P.
	By: PFM Health Sciences, LP, its investment advisor
		
	By:	 	 /s/ Yuan DuBord

	Name:	 	 Yuan DuBord

	Title:	 	 CFO

	
	PFM Healthcare Growth Equity Holdings I, LLC
	By: PFM Health Sciences GP, LLC, its member manager
		
	By:	 	 /s/ Yuan DuBord

	Name:	 	 Yuan DuBord

	Title:	 	 CFO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	ZONE III HEALTHCARE HOLDINGS, LLC
	
	By: Farallon Capital Management, L.L.C., its Manager
		
	By:	 	 /s/ Philip Dreyfuss

	Name:	 	 Philip Dreyfuss

	Title:	 	 Authorized Signatory

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	RIDGEBACK CAPITAL INVESTMENTS LP
	
	by RIDGEBACK CAPITAL MANAGEMENT LLC its Fund Manager:
		
	By:	 	 /s/ Christian Sheldon

	Name:	 	 Christian Sheldon

	Title:	 	 COO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	AbbVie Inc.
		
	By:	 	 /s/ Adam Houghton

	Name:	 	 Adam Houghton

	Title:	 	 VP & Head, AbbVie Ventures

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	MAVERICK VENTURES INVESTMENT FUND, L.P.
	
	By: Maverick Capital Ventures, LLC, its General Partner
	By: Maverick Capital Advisors, L.P., its Manager
		
	By:	 	 /s/ Ginessa Avila

	Name:	 	 Ginessa Avila

	Title:	 	 Authorized Signatory

	
	MAVERICK ADVISORS FUND, L.P.
	
	By: Maverick Capital Ventures, LLC, its General Partner
	By: Maverick Capital Advisors, L.P., its Manager
		
	By:	 	 /s/ Ginessa Avila

	Name:	 	 Ginessa Avila

	Title:	 	 Authorized Signatory

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Adage Capital Partners, LP
	By: Adage Capital Partners, GP, LLC, it’s General Partner
	By: Age Capital Advisors, LLC it’s Managing Member
		
	By:	 	 /s/ Dan Lehan

	Name:	 	 Dan Lehan

	Title:	 	 Chief Operating Officer

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
 INVESTOR: 

Janus Henderson Capital Funds plc on behalf of its series Janus Henderson Global Life Sciences Fund 

 

			
	By: Janus Capital Management LLC, its investment advisor
		
	By:	 	 /s/ Andrew Acker

	Name:	 	 Andrew Acker

	Title:	 	 Authorized Signatory

	
	Janus Henderson Biotech Innovation Master Fund Limited
	By: Janus Capital Management LLC, its investment advisor
		
	By:	 	 /s/ Andrew Acker

	Name:	 	 Andrew Acker

	Title:	 	 Authorized Signatory

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Monashee Solitario Fund LP
		
	By:	 	 /s/ Jeff Muller

	Name:	 	 Jeff Muller

	Title:	 	 COO

	
	DS Liquid Div RVA MON LLC
		
	By:	 	 /s/ Jeff Muller

	Name:	 	 Jeff Muller

	Title:	 	 COO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Point72 Biotech Private Investments, LLC
		
	By:	 	 /s/ Vincent Tortorella

	Name:	 	 Vincent Tortorella

	Title:	 	 Authorized Signatory

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	AngelList-Cces-Fund, a Series of AngelList-JR Funds, LLC
		
	By:	 	 /s/ Brett Sagan

	Name:	 	 Brett Sagan

	Title:	 	 Authorized Person

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	AngelList-Cces-PR-Fund, a series of AngelList-JR-Funds,
LLC
		
	By:	 	 /s/ Brett Sagan

	Name:	 	 Brett Sagan

	Title:	 	 Authorized Person

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Central Valley Administrators, Inc.
		
	By:	 	 /s/ Richard Merkin

	Name:	 	 Richard Merkin

	Title:	 	 President

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	CAROLEM CAPITAL LLC
		
	By:	 	 /s/ Michael Karlin

	Name:	 	 Michael Karlin

	Title:	 	 Manager

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	NRG CAPITAL HOLDINGS LLC
		
	By:	 	 /s/ Michael Karlin

	Name:	 	 Michael Karlin

	Title:	 	 Manager

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	LLS TAP, LLC
		
	By:	 	 /s/ Louis DeGennaro

	Name:	 	 Louis DeGennaro

	Title:	 	 President & CEO

		
	By:	 	 /s/ Gordon Miller

	Name:	 	 Gordon Miller

	Title:	 	 EVP & CFO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Tekla Healthcare Investors*
		
	By:	 	 /s/ Daniel R. Omstead

	Name:	 	 Daniel R. Omstead

	Title:	 	 President

  

	*	 The name Tekla Healthcare Investors is the designation of the Trustees for the time being under an
Amended & Restated Declaration of Trust dated April 21, 1987, as amended, and all persons dealing with Tekla Healthcare Investors must look solely to the trust property for the enforcement of any claim against Tekla Healthcare
Investors, as neither the Trustees, officers nor shareholders assume any personal liability for the obligations entered into on behalf of Tekla Healthcare Investors. 

 

			
	Tekla Life Sciences Investors*
		
	By:	 	 /s/ Daniel R. Omstead

	Name:	 	 Daniel R. Omstead

	Title:	 	 President

  

	*	 The name Tekla Life Sciences Investors is the designation of the Trustees for the time being under a
Declaration of Trust dated February 20, 1992, as amended, and all persons dealing with Tekla Life Sciences Investors must look solely to the trust property for the enforcement of any claim against Tekla Life Sciences Investors, as neither the
Trustees, officers nor shareholders assume any personal liability for the obligations entered into on behalf of Tekla Life Sciences Investors. 

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Jenny Rooke
		
	By:	 	 /s/ Jenny Rooke

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	PONTIFAX GLOBAL FOOD AND AGRICULTURE TECHNOLOGY FUND, L.P.
		
	By:	 	 /s/ Benjamin Belldegrun

	Name:	 	 Benjamin Belldegrun

	Title:	 	 Managing Partner

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	WS Investment Company, LLC (21A)
		
	By:	 	 /s/ James Terranova

	Name:	 	  

	Title:	 	  

	
	WS Investment Company, LLC (2014A)
		
	By:	 	 /s/ James Terranova

	Name:	 	  

	Title:	 	  

	
	WS Investment Company, LLC (2015A)
		
	By:	 	 /s/ James Terranova

	Name:	 	  

	Title:	 	  

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	James and Jennifer Doudna Cate Living Trust DTD 01/02/2014
		
	By:	 	 /s/ Jennifer Doudna

	Name:	 	 Jennifer Doudna

	Title:	 	 Trustee

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Mintz Levin Special Investments Fund LLC
		
	By:	 	 /s/ Megan N. Gates

	Name:	 	 Megan N. Gates

	Title:	 	 Member

	
	Mintz Levin Special Investments Fund LLC — Series FY21
		
	By:	 	 /s/ Megan N. Gates

	Name:	 	 Megan N. Gates

	Title:	 	 Member

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	James Berger & Marian Feldman
		
	By:	 	 /s/ James Berger

		
	By:	 	 /s/ Marian Feldman

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	E. I. du Pont de Nemours and Company
		
	By:	 	 /s/ George J. Duko

	Name:	 	 George J. Duko

	Title:	 	 Vice President, Mergers & Acquisitions

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	HEALTHCARE INNOVATION INVESTMENT FUND LLC
		
	By:	 	 /s/ Joseph R. Gentile

	Name:	 	 Joseph R. Gentile

	Title:	 	 Manager

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Pacific Continental Investment Company, LLC
		
	By:	 	 /s/ Marc Stridiron

	Name:	 	 Marc Stridiron

	Title:	 	 Portfolio Manager

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Pig Improvement Company UK Limited
		
	By:	 	 /s/ Stephen Wilson

	Name:	 	 Stephen Wilson

	Title:	 	 CEO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	LifeSci Venture Partners II, LP
		
	By:	 	 /s/ Paul Yook

	Name:	 	 Paul Yook

	Title:	 	 Managing Member

	
	LifeSci Venture Master SPV, LLC
		
	By:	 	 /s/ Paul Yook

	Name:	 	 Paul Yook

	Title:	 	 Managing Member

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Anterra F&A Ventures I Coöperatief U.A.
		
	By:	 	 /s/ Adam Anders

	Name:	 	 Adam Anders

	Title:	 	 Director

		
	By:	 	 /s/ Maarten Goossens

	Name:	 	 Maarten Goossens

	Title:	 	 Director

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	F-PRIME CAPITAL PARTNERS HEALTHCARE FUND IV LP
	
	By: F-Prime Capital Partners Healthcare Advisors Fund IV LP, its General Partner
	By: Impresa Holdings LLC, its General Partner
	By: Impresa Management LLC, its Managing Member
		
	By:	 	 /s/ Mary Bevelock Pendergast

	Name:	 	 Mary Bevelock Pendergast

	Title:	 	 Vice President

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Avego Bioscience Capital, L.P.
	By: Avego Bioscience Capital GP, LLC, its general partner
		
	By:	 	 /s/ James Flexner

	Name:	 	 James Flexner

	Title:	 	 Managing Partner

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Avidity Master Fund LP
		
	By:	 	 /s/ Michael Gregory

	Name:	 	 Michael Gregory

	Title:	 	 Director

	
	Avidity Capital Fund II LP
		
	By:	 	 /s/ Michael Gregory

	Name:	 	 Michael Gregory

	Title:	 	 Director

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Zachary A. Robbins Trust dtd December 31, 1987
		
	By:	 	 /s/ Rich Robbins

	Name:	 	 Rich Robbins

	Title:	 	 Trustee

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Robbins Family Trust of 1986
		
	By:	 	 /s/ Rich Robbins

	Name:	 	 Rich Robbins

	Title:	 	 Trustee

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Lucas Hamilton Robbins Trust dtd November 17, 1991
		
	By:	 	 /s/ Rich Robbins

	Name:	 	 Rich Robbins

	Title:	 	 Trustee

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Novartis Institutes for BioMedical Research, Inc.
		
	By:	 	 /s/ Scott A. Brown

	Name:	 	 Scott A Brown

	Title:	 	 VP CAO

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	INVUS PUBLIC EQUITIES, L.P.
		
	By:	 	 /s/ Raymond Debbane

	Name:	 	 Raymond Debbane

	Title:	 	 President of its General Partner

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	CA Fund I, a series of 5 Prime Ventures, LP
	By: Fund GP, LLC its General Partner
	By: Belltower Fund Group, Ltd. Manager of the General Partner
		
	By:	 	 /s/ Brett Sagan

	Name:	 	 Brett Sagan

	Title:	 	 Authorized Person

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

			
	INVESTOR:
	
	Rodolphe and Lisa Barrangou
		
	By:	 	 /s/ Rodolphe Barrangou

		
	By:	 	 /s/ Lisa Barrangou

 IN WITNESS WHEREOF, the parties have executed this Second Amended and Restated Right of
First Refusal and Co-Sale Agreement as of the date first written above. 
  

	
	KEY HOLDER
	
	 /s/ James Berger

	James Berger
	
	 /s/ Jennifer Doudna

	Jennifer Doudna
	
	 /s/ Rachel E. Haurwitz

	Rachel E. Haurwitz
	
	 /s/ Martin Jinek

	Martin Jinek
	
	  

	Andrew May

 SCHEDULE A 

INVESTORS 

 SCHEDULE B 

KEY HOLDERS 

 EXHIBIT A 

CONSENT OF SPOUSE 
 I,
[                    ], spouse of
[                    ], acknowledge that I have read the Second Amended and Restated Right of First Refusal and
Co-Sale Agreement, dated as of                      , 2021, to which this Consent is attached as Exhibit
A (the “Agreement”), and that I know the contents of the Agreement. I am aware that the Agreement contains provisions regarding certain rights to certain other holders of Capital Stock of the Company upon a Proposed Key Holder
Transfer of shares of Transfer Stock of the Company which my spouse may own including any interest I might have therein. 
 I hereby agree
that my interest, if any, in any shares of Transfer Stock of the Company subject to the Agreement shall be irrevocably bound by the Agreement and further understand and agree that any community property interest I may have in such shares of Transfer
Stock of the Company shall be similarly bound by the Agreement. 
 I am aware that the legal, financial and related matters contained in the
Agreement are complex and that I am free to seek independent professional guidance or counsel with respect to this Consent. I have either sought such guidance or counsel or determined after reviewing the Agreement carefully that I will waive such
right. 
 Dated as of the [    ] day of
[                ,     ]. 
  

	
	  

	Signature
	
	  

	Print NameEX-10.63

 Exhibit 10.63 

March 2, 2021 
 PFM Health Sciences, LP 

4 Embarcadero Center, Suite 3500 
 San Francisco, CA 94111 

Attn: Yuan DuBord 
 Re: Participation Rights 

This letter agreement (this “Agreement”) memorializes the agreement and understanding between PFM Health Sciences, LP
(“Investor”), on the one hand, and Caribou Biosciences, Inc., a Delaware corporation (the “Company”), on the other hand, regarding the Company’s grant to Investor of the right to participate in the
Company’s future initial public offering of its equity securities on the terms, and subject to the conditions, set forth below. 
 The Company is
entering into this Agreement as a material inducement to cause Investor to enter into that certain Series C Preferred Stock Purchase Agreement, dated as of the date hereof, by and among the Company, Investor, and the other purchasers named therein
(the “Purchase Agreement”). Capitalized terms not otherwise defined herein shall have the meanings ascribed to such terms in the Purchase Agreement and, to the extent not defined therein, such terms shall have the meanings ascribed
to them in that certain Second Amended and Restated Investors’ Rights Agreement, dated as of the date hereof, by and among the Company, Investor, and the parties named therein (the “IRA”). 

In consideration of the foregoing and the mutual promises and covenants hereinafter set forth and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, by execution of this Agreement, the parties hereto hereby agree as follows: 
 1. Public Offering
Participation Right. In connection with the Company’s sale of shares of its voting common stock (“Common Stock”) to the public in the first to occur of (a) the Company’s first firm-commitment underwritten public
offering pursuant to an effective registration statement under the Securities Act (an “IPO”) where a majority of the shares sold in such offering are newly issued shares of the Company or (b) the Company’s first
“direct public offering” pursuant to an effective registration statement under the Securities Act (a “DPO”) where (i) a majority of the shares sold in such offering are newly issued shares of the Company,
(ii) the price per share to the public is at least $21.572 (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Common Stock), and (iii) the
gross proceeds to the Company are at least $50,000,000 (a “Qualified DPO”), the Company shall, within a reasonable period of time preceding the consummation of such IPO or Qualified DPO and in compliance with and subject to all
applicable laws and regulations, use commercially reasonable efforts to provide Investor with the opportunity to purchase shares of Common Stock to be sold by the Company (for the avoidance of doubt, in such Qualified DPO, Investor’s
participation right shall not apply to the sale by any securityholders of their shares), in such IPO or Qualified DPO (including, in the case of an IPO, any over-allotment option by the underwriters to such IPO, if any (the “Overallotment
Option”)) at the same price per share at which the Common Stock offered in such IPO or Qualified DPO are being offered to the public (the “Public Price”) (such right, the “Public Offering Participation
Right”). If Investor exercises its Public Offering Participation Right, Investor shall have the right to purchase up to a number of shares of Common Stock to be sold in such IPO (excluding the Overallotment Option, if any) or Qualified DPO
equal to ten percent (10%) (the “Participation Right Percentage”) of the aggregate number of shares of Common Stock to be sold by the Company in such IPO (excluding, the Overallotment Option, if any) or Qualified DPO. In the case of
an IPO, in the event that any additional shares of Common Stock are sold by the Company in any exercise by the IPO underwriters of the Overallotment Option, then if Investor has exercised its Public Offering Participation Right in connection with
the IPO, Investor shall have the right to purchase up to a number of shares of Common Stock to be sold pursuant to the Overallotment Option equal to the Participation Right Percentage of the aggregate number of shares of Common Stock to be sold by
the Company pursuant to the Overallotment Option. Notwithstanding the preceding two sentences, in the event that in exercising the Public Offering Participation Right the number of shares of Common Stock held by Investor (including all shares of
Common Stock then issuable (directly or indirectly) upon conversion and/or exercise, as applicable, of the Preferred Stock and any other Derivative Securities then held by Investor) after such purchase(s) pursuant to the Public

 
Offering Participation Right (and after giving effect to the consummation of the IPO or Qualified DPO) would exceed ten percent (10%) of the total Common Stock then outstanding (assuming full
conversion and/or exercise, as applicable, of all Preferred Stock and other Derivative Securities) after giving effect to the consummation of the IPO, the Company and Investor shall comply with Section 5 below. Investor may assign its Public
Offering Participation Right to any of its Affiliates; provided, however, that the number of shares of Common Stock that may be purchased by Investor and its Affiliates in the aggregate pursuant to the Public Offering Participation Right and any
assignment(s) thereof shall not exceed the number of shares of Common Stock that Investor was originally entitled to purchase pursuant to the Public Offering Participation Right. For the avoidance of doubt, nothing in this Section 1 is intended
to limit the number of shares that Investor or its Affiliates may acquire in the IPO outside of its Public Offering Participation Right. Unless the context otherwise requires or is expressly provided otherwise, references in this Agreement to the
IPO shall include any exercised Overallotment Option. For the avoidance of doubt, the rights described in this Section 1 and Section 2 below shall apply only to the first to occur of an IPO or a Qualified DPO, in each case where a majority
of the shares sold in such offering are newly issued shares of the Company, and shall not apply to any subsequent offering of the Company’s securities. Notwithstanding anything to the contrary herein, if the Company proposes to consummate a DPO
that is not a Qualified DPO, the Company shall give Investor reasonable advance notice of such DPO and the proposed terms, and Investor shall have the right (in its sole discretion) to elect to deem such DPO to be a Qualified DPO for all purposes
under this Agreement. 
 2. Private Sale Participation Right. 

(a) Notwithstanding Section 1 above, in the event that either (i) the Company is advised by its outside legal counsel, the
Securities and Exchange Commission (the “SEC”), the Financial Industry Regulatory Authority (“FINRA”), or any stock exchange on which the Common Stock is to be traded (the “Exchange”) that the
offering or sale of the Company’s securities to Investor as described above in Section 1 would violate any federal or state securities laws or the rules or regulations of the SEC, FINRA, or the Exchange, (ii) in the case of an IPO,
the managing underwriter(s) reasonably determines that marketing factors require a limitation on the number of shares of Common Stock to be underwritten in connection with the IPO and request(s) that Investor’s Public Offering Participation
Right be subject to carve-backs, restrictions, or other limitations, or (iii) in the case of a Qualified DPO, the Company reasonably determines in good faith that such marketing factors require a limitation on the number of shares of Common
Stock to be sold by the Company in connection with the Qualified DPO and request(s) that Investor’s Public Offering Participation Right be subject to carve-backs, restrictions, or other limitations (each of the events described in the foregoing
clauses (i), (ii) or (iii), a “Cutback”), then, in each case, the Company shall offer to Investor the right to purchase in a separate private placement (the “Private Placement”) (which shall be conducted
concurrently with the IPO or Qualified DPO, as applicable, and the closing of which shall be contingent on the closing of such IPO or Qualified DPO), at the Public Price, up to that number of shares of Common Stock equal to the difference between
the number of shares of Common Stock that Investor would have been able to purchase pursuant to the Public Offering Participation Right in Section 1 above but for the applicable Cutback, and the number of shares of Common Stock that Investor
was actually permitted to purchase in such IPO or Qualified DPO pursuant to Section 1, if any (the “Private Sale Participation Right”). Notwithstanding anything to the contrary set forth above, (A) no such Cutback under
the foregoing clause (ii) or (iii) shall be imposed on Investor unless the number of shares of Common Stock that would otherwise be purchased by any other individual or entity to which the Company has granted, pursuant to a binding written
agreement, rights similar to the Public Offering Participation Right (the “Other Participating Investors”), excluding the other Lead Investors, has been cutback to zero, and (B) if any Cutback under the foregoing clause
(ii) or (iii) shall be imposed on Investor, such Cutback shall apply equally to the other Lead Investors with respect to the number of shares of Common Stock that Investor and the other Lead Investors are prohibited from purchasing upon
exercise of their respective rights. Investor may assign its Private Sale Participation Right to any of its Affiliates; provided, however, that the number of shares of Common Stock that may be purchased by Investor and its Affiliates in the
aggregate pursuant to the Private Sale Participation Right and any assignment(s) thereof shall not exceed the number of shares of Common Stock that Investor was originally entitled to purchase pursuant to the Private Sale Participation Right. Any
shares of Common Stock that Investor purchases in a Private Placement shall be exempt from the registration requirements of the Securities Act. 

(b) Notwithstanding the foregoing, Investor agrees that (i) in no event shall the Private Sale Participation Right be exercised in such a
manner that, in the reasonable determination of the managing underwriter(s), would materially and adversely affect the IPO or, in the case of a Qualified DPO, in the reasonable 

  
 2 

 
good faith determination of the Company, would materially and adversely affect the Qualified DPO, and (ii) the number of shares Investor is entitled to purchase may be reduced or modified
only to the extent reasonably requested by the Company’s underwriter(s) (or by the Company in the case of the Qualified DPO) as to not cause such material and adverse effect on the IPO or Qualified DPO, as the case may be; provided, however,
that (A) the number of shares of Common Stock that Investor is entitled to purchase may not be reduced or modified unless the number of shares of Common Stock that would otherwise be purchased in the Private Placement by any Other Participating
Investors, excluding the other Lead Investors, has been reduced to zero, and (B) if any such reduction or modification shall be imposed on Investor, such reduction or modification shall apply equally to the other Lead Investors with respect to
the number of shares of Common Stock that Investor and the other Lead Investors are prohibited from purchasing upon exercise of their respective rights. 

(c) If Investor exercises its Private Sale Participation Right, the Company and Investor shall execute and deliver such documents that are
(i) customary for a transaction structured as a concurrent private placement with a public offering, including without limitation customary resale registration rights, and (ii) reasonably satisfactory to the Company, Investor, and the
managing underwriter(s), if applicable. 
 3. SPAC Transaction Participation Right. If the Company proposes to enter into a SPAC Transaction (as
defined in the Certificate of Incorporation), and the SPAC (as defined in the Certificate of Incorporation) (or a parent or subsidiary of the SPAC) proposes to offer or sell securities in a private placement transaction that is contemporaneous with,
or otherwise connected to or conditioned on, such SPAC Transaction, the Company will use its commercially reasonable efforts, in compliance with and subject to all applicable laws and regulations, to ensure that Investor (or one or more of its
affiliates designated by Investor) is given the opportunity to purchase or otherwise acquire up to 10% of the total number of securities to be offered or sold in such private placement transaction, at the same price and on the same terms offered to
the other investors in such private placement transaction (and for such terms to include, without limitation, customary resale registration rights). The Company acknowledges and agrees that, for purposes of this Section 3, commercially
reasonable efforts shall include requesting that the sponsor or management of the SPAC (or of such parent or subsidiary of the SPAC) acknowledge and consider providing the benefit of such participation rights to Investor (or one or more of its
affiliates designated by Investor) in accordance with the immediately preceding sentence. 
 4. Private Placement Participation Right. If the
Company proposes to offer or sell securities in a private placement transaction that is substantially contemporaneous with or conditioned on an IPO (except pursuant to a Private Placement), a DPO (including a Qualified DPO, except pursuant to a
Private Placement) or a SPAC Transaction, the Company shall, in compliance with and subject to all applicable laws and regulations, offer Investor (or one or more of its affiliates designated by Investor) a right (but not an obligation) to purchase
or otherwise acquire up to 10% of the total number of securities to be offered or sold in such private placement transaction, at the same price and on the same terms offered to the other investors in such private placement transaction (and such
terms shall include, without limitation, customary resale registration rights); provided, however, that while the parties anticipate that such private placement transaction would not be subject to the right of first offer contained in
Section 4.1 of the IRA, in the event such right of first offer applied to such private placement transaction, then any amounts purchased by Investor pursuant to such right of first offer contained in the IRA shall count toward (and thereby
reduce) the amount of securities that Investor shall have the right to purchase in such private placement transaction pursuant to this Section 4. 
 5.
Beneficial Ownership Limitation. If, as a result of Investor’s exercise of its participation rights set forth herein in connection with an IPO, a DPO (including a Qualified DPO) or a SPAC Transaction, Investor would beneficially own (as
calculated in accordance with Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)) more than 9.99% of the outstanding shares of a class of voting equity securities of the Company, the SPAC or a
parent or subsidiary of the SPAC, as applicable, that is registered as a class under Section 12 of the Exchange Act (the “Public Shares”) as of immediately following the IPO, DPO or SPAC Transaction, as applicable, the Company
and Investor shall work together in good faith to use commercially reasonable efforts, in compliance with and subject to all applicable laws and regulations, to restructure Investor’s holdings such that Investor will not beneficially own more
than 9.99% of the outstanding Public Shares as of immediately following the IPO, DPO or SPAC Transaction, as applicable, with the remainder of Investor’s shares to be converted into non-voting shares or
warrants convertible or exercisable at Investor’s option into Public Shares only if such conversion or exercise would not result in Investor beneficially owning more than 9.99% of the then-outstanding Public Shares. 

  
 3 

 6. Representations and Warranties. Each party represents and warrants to the other party that
(a) this Agreement has been duly authorized and executed by such party and is a valid and binding obligation of such party, enforceable against such party in accordance with its terms, and (b) the execution of this Agreement is not
inconsistent with any of such party’s organizational documents, or any law applicable to such party, and does not conflict with or contravene any provision of, or constitute a default under, any contract or other instrument to which such party
is a party or by which it is bound. 
 7. Severability. The invalidity or unenforceability of any provision hereof shall in no way affect the
validity or enforceability of any other provision. 
 8. Amendments; Termination. This Agreement may not be modified, amended, or terminated, in
whole or in part, except by an agreement in writing signed by the parties hereto. The Company acknowledges and agrees that this Agreement shall not be amended, waived, canceled, terminated or superseded by any amendment to, or any restatement of,
the Purchase Agreement or the IRA, or by any other agreement entered into on or after the date hereof (whether or not it includes an integration clause), except with the prior written consent of Investor which expressly states that this Agreement is
so amended, terminated or superseded. Whether or not Investor exercises any of its participation rights under Section 1, 2, 3, or 4 of this Agreement, this Agreement shall automatically terminate and be of no further force or effect upon the
first to occur of (i) consummation of an IPO (and, if applicable, the Private Placement), (ii) consummation of a Qualified DPO (and, if applicable, the Private Placement), (iii) consummation of a SPAC Transaction, (iv) consummation of a
Deemed Liquidation Event (as defined in the Certificate of Incorporation), or (v) such time as Investor and its Affiliates no longer hold any of securities of the Company; provided that, in the case of the foregoing clauses (i) through
(iv), such termination shall not be effective until the Company has fulfilled all of its obligations under this Agreement with respect to such IPO (and, if applicable, the Private Placement), Qualified DPO, SPAC Transaction, or Deemed Liquidation
Event, as applicable. 
 9. Counterparts. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but
all of which together shall constitute one and the same instrument. Counterparts may be delivered via facsimile, electronic mail (including pdf or any electronic signature complying with the U.S. federal ESIGN Act of 2000, Uniform Electronic
Transactions Act or other applicable law), or other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes. 

10. Assignment; Successors and Assigns. This Agreement and all rights and obligations of Investor hereunder are personal to Investor and, except for
transfers or assignments to Affiliates and as otherwise expressly provided for herein, may not be transferred or assigned by Investor at any time without the Company’s prior written consent. This Agreement shall be binding upon and inure to the
benefit of the parties hereto and their respective permitted successors and permitted assigns. 
 11. Governing Law. The governing law and dispute
resolution provisions set forth in Section 6.3 and 6.12 of the Purchase Agreement are incorporated by reference herein, mutatis mutandis. 

(The remainder of this page left intentionally blank.)  

  
 4 

 Please confirm your agreement to the terms of this Agreement by counter-signature where indicated below.

  

			
	Sincerely,
	
	CARIBOU BIOSCIENCES, INC.
		
	By:	 	 /s/ Rachel E. Haurwitz

	Name:	 	Rachel E. Haurwitz
	Title:	 	President and Chief Executive Officer
	
	Accepted by:
	
	PFM HEALTH SCIENCES, LP
		
	By:	 	 /s/ Yuan DuBord

	Name:	 	Yuan DuBord
	Title:	 	Chief Financial Officer

 [Signature Page to Participation Rights Side Letter]

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