EX-10.2





 Exhibit 10.2 

SYNTHORX, INC. 

2014 EQUITY INCENTIVE PLAN 

ADOPTED BY THE BOARD OF DIRECTORS:
MAY 27, 2014 
 APPROVED BY THE STOCKHOLDERS:
MAY 27, 2014 
 AMENDED BY THE BOARD OF
DIRECTORS: JUNE 24, 2015 
 APPROVED BY THE
STOCKHOLDERS: JULY 20, 2015 
 AMENDED BY THE
BOARD OF DIRECTORS: JULY 12, 2016 
 APPROVED
BY THE STOCKHOLDERS: JULY 13, 2016 
 AMENDED
BY THE BOARD OF DIRECTORS: APRIL 11, 2018 

APPROVED BY THE STOCKHOLDERS: APRIL 11, 2018 

AMENDED BY THE BOARD OF DIRECTORS:
OCTOBER 25, 2018 
 APPROVED BY THE STOCKHOLDERS:
OCTOBER 29, 2018 
 TERMINATION DATE: MAY 26, 2024 

1.         GENERAL. 

(a)        Eligible Stock Award Recipients. Employees, Directors and
Consultants are eligible to receive Stock Awards. 
 (b)        Available
Stock Awards. The Plan provides for the grant of the following types of Stock Awards: (i) Incentive Stock Options, (ii) Nonstatutory Stock Options, (iii) Stock Appreciation Rights, (iv) Restricted Stock Awards,
(v) Restricted Stock Unit Awards and (vi) Other Stock Awards. 

(c)        Purpose. The Plan, through the granting of Stock Awards, is
intended to help the Company secure and retain the services of eligible award recipients, provide incentives for such persons to exert maximum efforts for the success of the Company and any Affiliate and provide a means by which the eligible
recipients may benefit from increases in value of the Common Stock. 
 2.         ADMINISTRATION.

 (a)        Administration by Board. The Board will administer the
Plan. The Board may delegate administration of the Plan to a Committee or Committees, as provided in Section 2(c). 

(b)        Powers of Board. The Board will have the power, subject to, and
within the limitations of, the express provisions of the Plan: 

(i)        To determine (A) who will be granted Stock Awards;
(B) when and how each Stock Award will be granted; (C) what type of Stock Award will be granted; (D) the provisions of each Stock Award (which need not be identical), including when a person will be permitted to exercise or otherwise
receive cash or Common Stock under the Stock Award; (E) the number of shares of Common Stock subject to a Stock Award; and (F) the Fair Market Value applicable to a Stock Award. 

  
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 (ii)        To construe and
interpret the Plan and Stock Awards granted under it, and to establish, amend and revoke rules and regulations for administration of the Plan and Stock Awards. The Board, in the exercise of these powers, may correct any defect, omission or
inconsistency in the Plan or in any Stock Award Agreement, in a manner and to the extent it will deem necessary or expedient to make the Plan or Stock Award fully effective. 

(iii)        To settle all controversies regarding the Plan and Stock Awards
granted under it. 
 (iv)        To accelerate, in whole or in part, the
time at which a Stock Award may be exercised or vest (or at which cash or shares of Common Stock may be issued). 

(v)        To suspend or terminate the Plan at any time. Except as otherwise
provided in the Plan or a Stock Award Agreement, suspension or termination of the Plan will not impair a Participant’s rights under his or her then-outstanding Stock Award without his or her written consent except as provided in subsection
(viii) below. 
 (vi)        To amend the Plan in any respect the Board
deems necessary or advisable, including, without limitation, by adopting amendments relating to Incentive Stock Options and certain nonqualified deferred compensation under Section 409A of the Code and/or to make the Plan or Stock Awards
granted under the Plan compliant with the requirements for Incentive Stock Options or exempt from or compliant with the requirements for nonqualified deferred compensation under Section 409A of the Code, subject to the limitations, if any, of
applicable law. However, if required by applicable law, and except as provided in Section 9(a) relating to Capitalization Adjustments, the Company will seek stockholder approval of any amendment of the Plan that (A) materially increases
the number of shares of Common Stock available for issuance under the Plan, (B) materially expands the class of individuals eligible to receive Stock Awards under the Plan, (C) materially increases the benefits accruing to Participants
under the Plan, (D) materially reduces the price at which shares of Common Stock may be issued or purchased under the Plan, (E) materially extends the term of the Plan, or (F) materially expands the types of Stock Awards available for
issuance under the Plan. Except as provided in the Plan (including subsection (viii) below) or a Stock Award Agreement, no amendment of the Plan will impair a Participant’s rights under an outstanding Stock Award unless (1) the
Company requests the consent of the affected Participant, and (2) such Participant consents in writing. 

(vii)        To submit any amendment to the Plan for stockholder approval,
including, but not limited to, amendments to the Plan intended to satisfy the requirements of Section 422 of the Code regarding Incentive Stock Options. 

(viii)        To approve forms of Stock Award Agreements for use under the
Plan and to amend the terms of any one or more Stock Awards, including, but not limited to, amendments to provide terms more favorable to the Participant than previously provided in the Stock Award Agreement, subject to any specified limits in the
Plan that are not subject to Board discretion; provided however, that a Participant’s rights under any Stock Award will not be impaired by any such amendment unless (A) the Company requests the consent of the affected Participant,
and (B) such Participant consents in writing. Notwithstanding the foregoing, (1) a Participant’s rights 

  
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will not be deemed to have been impaired by any such amendment if the Board, in its sole discretion, determines that the amendment, taken as a whole, does not materially impair the
Participant’s rights, and (2) subject to the limitations of applicable law, if any, the Board may amend the terms of any one or more Stock Awards without the affected Participant’s consent (A) to maintain the qualified status of
the Stock Award as an Incentive Stock Option under Section 422 of the Code; (B) to change the terms of an Incentive Stock Option, if such change results in impairment of the Award solely because it impairs the qualified status of the Award
as an Incentive Stock Option under Section 422 of the Code; (C) to clarify the manner of exemption from, or to bring the Stock Award into compliance with, Section 409A of the Code; or (D) to comply with other applicable laws.

 (ix)        Generally, to exercise such powers and to perform such acts
as the Board deems necessary or expedient to promote the best interests of the Company and that are not in conflict with the provisions of the Plan or Stock Awards. 

(x)        To adopt such procedures and
sub-plans as are necessary or appropriate to permit participation in the Plan by Employees, Directors or Consultants who are foreign nationals or employed outside the United States (provided that Board
approval will not be necessary for immaterial modifications to the Plan or any Stock Award Agreement that are required for compliance with the laws of the relevant foreign jurisdiction). 

(xi)        To effect, with the consent of any adversely affected Participant,
(A) the reduction of the exercise, purchase or strike price of any outstanding Stock Award; (B) the cancellation of any outstanding Stock Award and the grant in substitution therefor of a new (1) Option or SAR, (2) Restricted
Stock Award, (3) Restricted Stock Unit Award, (4) Other Stock Award, (5) cash and/or (6) other valuable consideration determined by the Board, in its sole discretion, with any such substituted award (x) covering the same or
a different number of shares of Common Stock as the cancelled Stock Award and (y) granted under the Plan or another equity or compensatory plan of the Company; or (C) any other action that is treated as a repricing under generally accepted
accounting principles. 
 (c)        Delegation to Committee. The Board may
delegate some or all of the administration of the Plan to a Committee or Committees. If administration of the Plan 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 of the Committee 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). Any delegation of administrative powers will be reflected in resolutions, not inconsistent with the provisions of the Plan, adopted from time to time by the Board or Committee (as applicable).
The Committee may, at any time, abolish the subcommittee and/or revest in the Committee any powers delegated to the subcommittee. 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)        Delegation to an Officer. The Board may delegate to one
(1) or more Officers the authority to do one or both of the following: (i) designate Employees who are not Officers to be 

  
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recipients of Options and SARs (and, to the extent permitted by applicable law, other Stock Awards) and, to the extent permitted by applicable law, the terms of such Stock Awards, and
(ii) determine the number of shares of Common Stock to be subject to such Stock Awards granted to such Employees; provided, however, that the Board resolutions regarding such delegation will specify the total number of shares of Common Stock
that may be subject to the Stock Awards granted by such Officer and that such Officer may not grant a Stock Award to himself or herself. Any such Stock Awards will be granted on the form of Stock Award Agreement most recently approved for use by the
Committee or the Board, unless otherwise provided in the resolutions approving the delegation authority. The Board may not delegate authority to an Officer who is acting solely in the capacity of an Officer to determine the Fair Market Value
pursuant to Section 13(t) below. 
 (e)        Effect of
Board’s Decision. 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. 

(f)        Arbitration. Any dispute or claim concerning any Stock Awards
granted (or not granted) or any disputes or claims relating to or arising out of the Plan will be fully, finally and exclusively resolved by binding and confidential arbitration conducted pursuant to the rules of Judicial Arbitration and Mediation
Services, Inc. (“JAMS”) in the city or county in which the Company’s principal offices are then located. The Company will pay all arbitration fees. In addition to any other relief, the arbitrator may award to
the prevailing party recovery of its attorneys’ fees and costs. By accepting a Stock Award, Participants and the Company waive their respective rights to have any such disputes or claims tried by a judge or jury. 

3.         SHARES SUBJECT TO THE PLAN.

 (a)        Share Reserve. 

(i)        Subject to Section 9(a) relating to Capitalization
Adjustments, the aggregate number of shares of Common Stock that may be issued pursuant to Stock Awards from and after the Effective Date will not exceed 5,049,277 shares (the
“Share Reserve”). 

(ii)        For clarity, the Share Reserve in this Section 3(a) is a
limitation on the number of shares of Common Stock that may be issued under the Plan. Accordingly, this Section 3(a) does not limit the granting of Stock Awards except as provided in Section 7(a). 

(b)        Reversion of Shares to the Share Reserve. If a Stock Award or
any portion thereof (i) expires or otherwise terminates without all of the shares covered by such Stock Award having been issued or (ii) is settled in cash (i.e., the Participant receives cash rather than stock), such expiration,
termination or settlement will not reduce (or otherwise offset) the number of shares of Common Stock that may be available for issuance under the Plan. If any shares of Common Stock issued pursuant to a Stock Award are forfeited back to or
repurchased by the Company because of the failure to meet a contingency or condition required to vest such shares in the Participant, then the shares that are forfeited or repurchased will revert to and again become available for issuance under the
Plan. Any shares reacquired by the Company in satisfaction of 

  
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tax withholding obligations on a Stock Award or as consideration for the exercise or purchase price of a Stock Award will again become available for issuance under the Plan. 

(c)        Incentive Stock Option Limit. Subject to the Share Reserve
and Section 9(a) relating to Capitalization Adjustments, the aggregate maximum number of shares of Common Stock that may be issued pursuant to the exercise of Incentive Stock Options will be 10,098,554 shares of Common Stock. 

(d)        Source of Shares. The stock issuable under the Plan will be shares
of authorized but unissued or reacquired Common Stock, including shares repurchased by the Company on the open market or otherwise. 

4.          ELIGIBILITY. 

 (a)        Eligibility for Specific Stock Awards. Incentive Stock Options
may be granted only to employees of the Company or a “parent corporation” or “subsidiary corporation” thereof (as such terms are defined in Sections 424(e) and 424(f) of the Code). Stock Awards other than Incentive Stock
Options may be granted to Employees, Directors and Consultants; provided, however, that Stock Awards may not be granted to Employees, Directors and Consultants who are providing Continuous Service only to any “parent” of the
Company, as such term is defined in Rule 405, unless (i) the stock underlying such Stock Awards is treated as “service recipient stock” under Section 409A of the Code (for example, because the Stock Awards are granted
pursuant to a corporate transaction such as a spin off transaction), or (ii) the Company, in consultation with its legal counsel, has determined that such Stock Awards are otherwise exempt from or alternatively comply with the distribution
requirements of Section 409A of the Code. 
  (b)        Ten
Percent Stockholders. A Ten Percent Stockholder will not be granted an Incentive Stock Option unless the exercise price of such Option is at least one hundred ten percent (110%) of the Fair Market Value on the date of grant and the Option
is not exercisable after the expiration of five (5) years from the date of grant. 
  (c)
        Consultants. A Consultant will not be eligible for the grant of a Stock Award if, at the time of grant, either the offer or sale of the Company’s securities to such Consultant is not exempt
under Rule 701 because of the nature of the services that the Consultant is providing to the Company, because the Consultant is not a natural person, or because of any other provision of Rule 701, unless the Company determines that such
grant need not comply with the requirements of Rule 701 and will satisfy another exemption under the Securities Act as well as comply with the securities laws of all other relevant jurisdictions. 

5.        PROVISIONS RELATING TO OPTIONS
AND STOCK APPRECIATION RIGHTS. 
 Each Option or SAR will be in such form
and will contain such terms and conditions as the Board deems appropriate. All Options will be separately designated Incentive Stock Options or Nonstatutory Stock Options at the time of grant, and, if certificates are issued, a separate certificate
or certificates will be issued for shares of Common Stock purchased on exercise of each type of Option. If an Option is not specifically designated as an Incentive Stock Option, or if an 

  
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Option is designated as an Incentive Stock Option but some portion or all of the Option fails to qualify as an Incentive Stock Option under the applicable rules, then the Option (or portion
thereof) will be a Nonstatutory Stock Option. The provisions of separate Options or SARs need not be identical; provided, however, that each Stock Award Agreement will conform to (through incorporation of provisions hereof by reference in the
applicable Stock Award Agreement or otherwise) the substance of each of the following provisions: 

(a)        Term. Subject to the provisions of Section 4(b) regarding Ten
Percent Stockholders, no Option or SAR will be exercisable after the expiration of ten (10) years from the date of its grant or such shorter period specified in the Stock Award Agreement. 

(b)        Exercise Price. Subject to the provisions of Section 4(b)
regarding Ten Percent Stockholders, the exercise or strike price of each Option or SAR will be not less than one hundred percent (100%) of the Fair Market Value of the Common Stock subject to the Option or SAR on the date the Stock Award is
granted. Notwithstanding the foregoing, an Option or SAR may be granted with an exercise or strike price lower than one hundred percent (100%) of the Fair Market Value of the Common Stock subject to the Stock Award if such Stock Award is
granted pursuant to an assumption of or substitution for another option or stock appreciation right pursuant to a Corporate Transaction and in a manner consistent with the provisions of Section 409A of the Code and, if applicable,
Section 424(a) of the Code. Each SAR will be denominated in shares of Common Stock equivalents. 

(c)        Purchase Price for Options. The purchase price of Common
Stock acquired pursuant to the exercise of an Option may be paid, to the extent permitted by applicable law and as determined by the Board in its sole discretion, by any combination of the methods of payment set forth below. The Board will have the
authority to grant Options that do not permit all of the following methods of payment (or otherwise restrict the ability to use certain methods) and to grant Options that require the consent of the Company to use a particular method of payment. The
permitted methods of payment are as follows: 
 (i)        by cash, check,
bank draft or money order payable to the Company; 
 (ii)        pursuant to
a program developed under Regulation T as promulgated by the Federal Reserve Board that, prior to the issuance of the stock subject to the Option, results in either the receipt of cash (or check) by the Company or the receipt of irrevocable
instructions to pay the aggregate exercise price to the Company from the sales proceeds; 

(iii)        by delivery to the Company (either by actual delivery or
attestation) of shares of Common Stock; 
 (iv)        if an Option is a
Nonstatutory Stock Option, by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Common Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not
exceed the aggregate exercise price; provided, however, that the Company will accept a cash or other payment from the Participant to the extent of any remaining balance of the aggregate exercise price not satisfied by such reduction in the number of
whole shares to be issued. Shares 

  
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of Common Stock will no longer be subject to an Option and will not be exercisable thereafter to the extent that (A) shares issuable upon exercise are used to pay the exercise price pursuant
to the “net exercise,” (B) shares are delivered to the Participant as a result of such exercise, and (C) shares are withheld to satisfy tax withholding obligations; 

(v)        according to a deferred payment or similar arrangement with the
Optionholder; provided, however, that interest will compound at least annually and will be charged at the minimum rate of interest necessary to avoid (A) the imputation of interest income to the Company and compensation income to the
Optionholder under any applicable provisions of the Code, and (B) the classification of the Option as a liability for financial accounting purposes; or 

(vi)        in any other form of legal consideration that may be acceptable to
the Board and specified in the applicable Stock Award Agreement. 

(d)         Exercise and Payment of a SAR. To exercise any
outstanding SAR, the Participant must provide written notice of exercise to the Company in compliance with the provisions of the Stock Award Agreement evidencing such SAR. The appreciation distribution payable on the exercise of a SAR will be not
greater than an amount equal to the excess of (A) the aggregate Fair Market Value (on the date of the exercise of the SAR) of a number of shares of Common Stock equal to the number of Common Stock equivalents in which the Participant is vested
under such SAR, and with respect to which the Participant is exercising the SAR on such date, over (B) the aggregate strike price of the number of Common Stock equivalents with respect to which the Participant is exercising the SAR on such
date. The appreciation distribution may be paid in Common Stock, in cash, in any combination of the two or in any other form of consideration, as determined by the Board and contained in the Stock Award Agreement evidencing such SAR. 

(e)         Transferability of Options and SARs. The Board may, in its
sole discretion, impose such limitations on the transferability of Options and SARs as the Board will determine. In the absence of such a determination by the Board to the contrary, the following restrictions on the transferability of Options and
SARs will apply: 
 (i)        Restrictions on Transfer. An Option or SAR
will not be transferable except by will or by the laws of descent and distribution (and pursuant to subsections (ii) and (iii) below), and will be exercisable during the lifetime of the Participant only by the Participant. The Board may permit
transfer of the Option or SAR in a manner that is not prohibited by applicable tax and securities laws. Except as explicitly provided herein, neither an Option nor a SAR may be transferred for consideration. 

(ii)        Domestic Relations Orders. Subject to the approval of the Board or
a duly authorized Officer, an Option or SAR may be transferred pursuant to the terms of a domestic relations order, official marital settlement agreement or other divorce or separation instrument as permitted by Treasury Regulation 1.421-1(b)(2). If an Option is an Incentive Stock Option, such Option may be deemed to be a Nonstatutory Stock Option as a result of such transfer. 

  
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 (iii)        Beneficiary
Designation. Subject to the approval of the Board or a duly authorized Officer, a Participant may, by delivering written notice to the Company, in a form approved by the Company (or the designated broker), designate a third party who, upon the
death of the Participant, will thereafter be entitled to exercise the Option or SAR and receive the Common Stock or other consideration resulting from such exercise. In the absence of such a designation, upon the death of the Participant, the
executor or administrator of the Participant’s estate will be entitled to exercise the Option or SAR and receive the Common Stock or other consideration resulting from such exercise. However, the Company may prohibit designation of a
beneficiary at any time, including due to any conclusion by the Company that such designation would be inconsistent with the provisions of applicable laws. 

(f)        Vesting Generally. The total number of shares of Common Stock
subject to an Option or SAR may vest and become exercisable in periodic installments that may or may not be equal. The Option or SAR may be subject to such other terms and conditions on the time or times when it may or may not be exercised (which
may be based on the satisfaction of performance goals or other criteria) as the Board may deem appropriate. The vesting provisions of individual Options or SARs may vary. The provisions of this Section 5(f) are subject to any Option or SAR
provisions governing the minimum number of shares of Common Stock as to which an Option or SAR may be exercised. 

(g)        Termination of Continuous Service. Except as otherwise provided in
the applicable Stock Award Agreement or other agreement between the Participant and the Company, if a Participant’s Continuous Service terminates (other than for Cause and other than upon the Participant’s death or Disability), the
Participant may exercise his or her Option or SAR (to the extent that the Participant was entitled to exercise such Stock Award as of the date of termination of Continuous Service) within the period of time ending on the earlier of (i) the date
three (3) months following the termination of the Participant’s Continuous Service (or such longer or shorter period specified in the applicable Stock Award Agreement, which period will not be less than thirty (30) days if
necessary to comply with applicable laws unless such termination is for Cause) and (ii) the expiration of the term of the Option or SAR as set forth in the Stock Award Agreement. If, after termination of Continuous Service, the Participant does
not exercise his or her Option or SAR within the applicable time frame, the Option or SAR (as applicable) will terminate. 

(h)        Extension of Termination Date. Except as otherwise provided
in the applicable Stock Award Agreement or other agreement between the Participant and the Company, if the exercise of an Option or SAR following the termination of the Participant’s Continuous Service (other than for Cause and other than upon
the Participant’s death or Disability) would be prohibited at any time solely because the issuance of shares of Common Stock would violate the registration requirements under the Securities Act, then the Option or SAR will terminate on the
earlier of (i) the expiration of a period of three (3) months after the termination of the Participant’s Continuous Service during which the exercise of the Option or SAR would not be in violation of such registration
requirements, or (ii) the expiration of the term of the Option or SAR as set forth in the applicable Stock Award Agreement. In addition, unless otherwise provided in a Participant’s Stock Award Agreement, if the sale of any Common Stock
received upon exercise 

  
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of an Option or SAR following the termination of the Participant’s Continuous Service (other than for Cause) would violate the Company’s insider trading policy, then the Option or SAR
will terminate on the earlier of (i) the expiration of a period of time (that need not be consecutive) equal to the applicable post-termination exercise period after the termination of the Participant’s Continuous Service during which the
sale of the Common Stock received upon exercise of the Option or SAR would not be in violation of the Company’s insider trading policy, or (ii) the expiration of the term of the Option or SAR as set forth in the applicable Stock Award
Agreement. 
 (i)        Disability of Participant. Except as
otherwise provided in the applicable Stock Award Agreement or other agreement between the Participant and the Company, if a Participant’s Continuous Service terminates as a result of the Participant’s Disability, the Participant may
exercise his or her Option or SAR (to the extent that the Participant was entitled to exercise such Option or SAR as of the date of termination of Continuous Service), but only within such period of time ending on the earlier of (i) the date
twelve (12) months following such termination of Continuous Service (or such longer or shorter period specified in the Stock Award Agreement, which period will not be less than six (6) months if necessary to comply with
applicable laws), and (ii) the expiration of the term of the Option or SAR as set forth in the Stock Award Agreement. If, after termination of Continuous Service, the Participant does not exercise his or her Option or SAR within the applicable
time frame, the Option or SAR (as applicable) will terminate. 
 (j)        Death
of Participant. Except as otherwise provided in the applicable Stock Award Agreement or other agreement between the Participant and the Company, if (i) a Participant’s Continuous Service terminates as a result of the Participant’s
death, or (ii) the Participant dies within the period (if any) specified in the Stock Award Agreement for exercisability after the termination of the Participant’s Continuous Service (for a reason other than death), then the Option or SAR
may be exercised (to the extent the Participant was entitled to exercise such Option or SAR as of the date of death) by the Participant’s estate, by a person who acquired the right to exercise the Option or SAR by bequest or inheritance or by a
person designated to exercise the Option or SAR upon the Participant’s death, but only within the period ending on the earlier of (i) the date eighteen (18) months following the date of death (or such longer or shorter period
specified in the Stock Award Agreement, which period will not be less than six (6) months if necessary to comply with applicable laws), and (ii) the expiration of the term of such Option or SAR as set forth in the Stock Award
Agreement. If, after the Participant’s death, the Option or SAR is not exercised within the applicable time frame, the Option or SAR (as applicable) will terminate. 

(k)        Termination for Cause. Except as explicitly provided
otherwise in a Participant’s Stock Award Agreement or other individual written agreement between the Company or any Affiliate and the Participant, if a Participant’s Continuous Service is terminated for Cause, the Option or SAR will
terminate immediately upon such Participant’s termination of Continuous Service, and the Participant will be prohibited from exercising his or her Option or SAR from and after the time of such termination of Continuous Service. 

(l)        Non-Exempt Employees. If an
Option or SAR is granted to an Employee who is a non-exempt employee for purposes of the Fair Labor Standards Act of 1938, as amended, the 

  
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Option or SAR will not be first exercisable for any shares of Common Stock until at least six (6) months following the date of grant of the Option or SAR (although the Stock Award may vest
prior to such date). Consistent with the provisions of the Worker Economic Opportunity Act, (i) if such non-exempt Employee dies or suffers a Disability, (ii) upon a Corporate Transaction in which
such Option or SAR is not assumed, continued, or substituted, (iii) upon a Change in Control, or (iv) upon the Participant’s retirement (as such term may be defined in the Participant’s Stock Award Agreement, in another agreement
between the Participant and the Company, or, if no such definition, in accordance with the Company’s then current employment policies and guidelines), the vested portion of any Options and SARs may be exercised earlier than six (6) months
following the date of grant. The foregoing provision is intended to operate so that any income derived by a non-exempt employee in connection with the exercise or vesting of an Option or SAR will be exempt
from his or her regular rate of pay. To the extent permitted and/or required for compliance with the Worker Economic Opportunity Act to ensure that any income derived by a non-exempt employee in connection
with the exercise, vesting or issuance of any shares under any other Stock Award will be exempt from the employee’s regular rate of pay, the provisions of this Section 5(l) will apply to all Stock Awards and are hereby incorporated by
reference into such Stock Award Agreements. 
 (m)        Early Exercise of
Options. An Option may, but need not, include a provision whereby the Optionholder may elect at any time before the Optionholder’s Continuous Service terminates to exercise the Option as to any part or all of the shares of Common Stock
subject to the Option prior to the full vesting of the Option. Subject to the “Repurchase Limitation” in Section 8(l), any unvested shares of Common Stock so purchased may be subject to a repurchase right in favor of the Company
or to any other restriction the Board determines to be appropriate. Provided that the “Repurchase Limitation” in Section 8(l) is not violated, the Company will not be required to exercise its repurchase right until at least
six (6) months (or such longer or shorter period of time required to avoid classification of the Option as a liability for financial accounting purposes) have elapsed following exercise of the Option unless the Board otherwise specifically
provides in the Option Agreement. 
 (n)        Right of Repurchase. Subject
to the “Repurchase Limitation” in Section 8(l), the Option or SAR may include a provision whereby the Company may elect to repurchase all or any part of the vested shares of Common Stock acquired by the Participant pursuant to
the exercise of the Option or SAR. 
 (o)        Right of First
Refusal. The Option or SAR may include a provision whereby the Company may elect to exercise a right of first refusal following receipt of notice from the Participant of the intent to transfer all or any part of the shares of Common Stock
received upon the exercise of the Option or SAR. Such right of first refusal will be subject to the “Repurchase Limitation” in Section 8(l). Except as expressly provided in this Section 5(o) or in the Stock Award Agreement,
such right of first refusal will otherwise comply with any applicable provisions of the bylaws of the Company. 

  
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 6.         PROVISIONS OF
STOCK AWARDS OTHER THAN OPTIONS AND SARS. 

(a)        Restricted Stock Awards. Each Restricted Stock Award
Agreement will be in such form and will contain such terms and conditions as the Board deems appropriate. To the extent consistent with the Company’s bylaws, at the Board’s election, shares of Common Stock underlying a Restricted Stock
Award may be (i) held in book entry form subject to the Company’s instructions until any restrictions relating to the Restricted Stock Award lapse; or (ii) evidenced by a certificate, which certificate will be held in such form and
manner as determined by the Board. The terms and conditions of Restricted Stock Award Agreements may change from time to time, and the terms and conditions of separate Restricted Stock Award Agreements need not be identical. Each Restricted Stock
Award Agreement will conform to (through incorporation of the provisions hereof by reference in the agreement or otherwise) the substance of each of the following provisions: 

(i)        Consideration. A Restricted Stock Award may be awarded in
consideration for (A) cash, check, bank draft or money order payable to the Company, (B) past services to the Company or an Affiliate, or (C) any other form of legal consideration (including future services) that may be
acceptable to the Board, in its sole discretion, and permissible under applicable law. 

(ii)        Vesting. Subject to the “Repurchase Limitation” in
Section 8(l), shares of Common Stock awarded under the Restricted Stock Award Agreement may be subject to forfeiture to the Company in accordance with a vesting schedule to be determined by the Board. 

(iii)        Termination of Participant’s Continuous Service. If a
Participant’s Continuous Service terminates, the Company may receive through a forfeiture condition or a repurchase right, any or all of the shares of Common Stock held by the Participant as of the date of termination of Continuous Service
under the terms of the Restricted Stock Award Agreement. 

(iv)        Transferability. Rights to acquire shares of Common Stock under
the Restricted Stock Award Agreement will be transferable by the Participant only upon such terms and conditions as are set forth in the Restricted Stock Award Agreement, as the Board will determine in its sole discretion, so long as Common Stock
awarded under the Restricted Stock Award Agreement remains subject to the terms of the Restricted Stock Award Agreement. 

(v)        Dividends. A Restricted Stock Award Agreement may provide that any
dividends paid on Restricted Stock will be subject to the same vesting and forfeiture restrictions as apply to the shares subject to the Restricted Stock Award to which they relate. 

(b)        Restricted Stock Unit Awards. Each Restricted Stock Unit Award
Agreement will be in such form and will contain such terms and conditions as the Board deems appropriate. The terms and conditions of Restricted Stock Unit Award Agreements may change from time to time, and the terms and conditions of separate
Restricted Stock Unit Award Agreements need not be identical. Each Restricted Stock Unit Award Agreement will conform to (through incorporation of the provisions hereof by reference in the Agreement or otherwise) the substance of each of the
following provisions: 

  
 11. 














(i)        Consideration. At the time of grant of a Restricted Stock
Unit Award, the Board will determine the consideration, if any, to be paid by the Participant upon delivery of each share of Common Stock subject to the Restricted Stock Unit Award. The consideration to be paid (if any) by the Participant for each
share of Common Stock subject to a Restricted Stock Unit Award may be paid in any form of legal consideration that may be acceptable to the Board, in its sole discretion, and permissible under applicable law. 

(ii)        Vesting. At the time of the grant of a Restricted Stock
Unit Award, the Board may impose such restrictions on or conditions to the vesting of the Restricted Stock Unit Award as it, in its sole discretion, deems appropriate. 

(iii)        Payment. A Restricted Stock Unit Award may be settled by
the delivery of shares of Common Stock, their cash equivalent, any combination thereof or in any other form of consideration, as determined by the Board and contained in the Restricted Stock Unit Award Agreement. 

(iv)        Additional Restrictions. At the time of the grant of a
Restricted Stock Unit Award, the Board, as it deems appropriate, may impose such restrictions or conditions that delay the delivery of the shares of Common Stock (or their cash equivalent) subject to a Restricted Stock Unit Award to a time after the
vesting of such Restricted Stock Unit Award. 
 (v)        Dividend
Equivalents. Dividend equivalents may be credited in respect of shares of Common Stock covered by a Restricted Stock Unit Award, as determined by the Board and contained in the Restricted Stock Unit Award Agreement. At the sole discretion of the
Board, such dividend equivalents may be converted into additional shares of Common Stock covered by the Restricted Stock Unit Award in such manner as determined by the Board. Any additional shares covered by the Restricted Stock Unit Award credited
by reason of such dividend equivalents will be subject to all of the same terms and conditions of the underlying Restricted Stock Unit Award Agreement to which they relate. 

(vi)        Termination of Participant’s Continuous Service.
Except as otherwise provided in the applicable Restricted Stock Unit Award Agreement, such portion of the Restricted Stock Unit Award that has not vested will be forfeited upon the Participant’s termination of Continuous Service. 

 (vii)        Compliance with Section 409A of the Code.
Notwithstanding anything to the contrary set forth herein, any Restricted Stock Unit Award granted under the Plan that is not exempt from the requirements of Section 409A of the Code shall contain such provisions so that such Restricted Stock
Unit Award will comply with the requirements of Section 409A of the Code. Such restrictions, if any, shall be determined by the Board and contained in the Restricted Stock Unit Award Agreement evidencing such Restricted Stock Unit Award. For
example, such restrictions may include, without limitation, a requirement that any Common Stock that is to be issued in a year following the year in which the Restricted Stock Unit Award vests must be issued in accordance with a fixed pre-determined schedule. 

  
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 (c)        Other Stock
Awards. Other forms of Stock Awards valued in whole or in part by reference to, or otherwise based on, Common Stock, including the appreciation in value thereof (e.g., options or stock rights with an exercise price or strike price less than one
hundred percent (100%) of the Fair Market Value of the Common Stock at the time of grant) may be granted either alone or in addition to Stock Awards provided for under Section 5 and the preceding provisions of this Section 6. Subject to
the provisions of the Plan, the Board will have sole and complete authority to determine the persons to whom and the time or times at which such Other Stock Awards will be granted, the number of shares of Common Stock (or the cash equivalent
thereof) to be granted pursuant to such Other Stock Awards and all other terms and conditions of such Other Stock Awards. 

7.          COVENANTS OF THE COMPANY.

 (a)        Availability of Shares. The Company will keep
available at all times the number of shares of Common Stock reasonably required to satisfy then-outstanding Stock Awards. 

(b)        Securities Law Compliance. The Company will seek to obtain from each
regulatory commission or agency having jurisdiction over the Plan such authority as may be required to grant Stock Awards and to issue and sell shares of Common Stock upon exercise of the Stock Awards; provided, however, that this undertaking
will not require the Company to register under the Securities Act the Plan, any Stock Award or any Common Stock issued or issuable pursuant to any such Stock Award. If, after reasonable efforts and at a reasonable cost, the Company is unable to
obtain from any such regulatory commission or agency the authority that counsel for the Company deems necessary for the lawful issuance and sale of Common Stock under the Plan, the Company will be relieved from any liability for failure to issue and
sell Common Stock upon exercise of such Stock Awards unless and until such authority is obtained. A Participant will not be eligible for the grant of a Stock Award or the subsequent issuance of cash or Common Stock pursuant to the Stock Award if
such grant or issuance would be in violation of any applicable securities law. 

(c)        No Obligation to Notify or Minimize Taxes. The Company will have no
duty or obligation to any Participant to advise such holder as to the time or manner of exercising such Stock Award. Furthermore, the Company will have no duty or obligation to warn or otherwise advise such holder of a pending termination or
expiration of a Stock Award or a possible period in which the Stock Award may not be exercised. The Company has no duty or obligation to minimize the tax consequences of a Stock Award to the holder of such Stock Award. 

8.          MISCELLANEOUS. 

(a)        Use of Proceeds from Sales of Common Stock. Proceeds from the sale
of shares of Common Stock pursuant to Stock Awards will constitute general funds of the Company. 

(b)        Corporate Action Constituting Grant of Stock Awards. Corporate
action constituting a grant by the Company of a Stock Award to any Participant will be deemed completed as of the date of such corporate action, unless otherwise determined by the Board, regardless of when the instrument, certificate, or letter
evidencing the Stock Award is communicated to, or 

  
 13. 













 
actually received or accepted by, the Participant. In the event that the corporate records (e.g., Board consents, resolutions or minutes) documenting the corporate action constituting the grant
contain terms (e.g., exercise price, vesting schedule or number of shares) that are inconsistent with those in the Stock Award Agreement as a result of a clerical error in the papering of the Stock Award Agreement, the corporate records will control
and the Participant will have no legally binding right to the incorrect term in the Stock Award Agreement. 

(c)        Stockholder Rights. No Participant will be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any shares of Common Stock subject to a Stock Award unless and until (i) such Participant has satisfied all requirements for exercise of, or the issuance of shares of Common Stock
under, the Stock Award pursuant to its terms, and (ii) the issuance of the Common Stock subject to the Stock Award has been entered into the books and records of the Company. 

(d)        No Employment or Other Service Rights. Nothing in the Plan, any
Stock Award Agreement or any other instrument executed thereunder or in connection with any Stock Award granted pursuant thereto will confer upon any Participant any right to continue to serve the Company or an Affiliate in the capacity in effect at
the time the Stock Award was granted or will affect the right of the Company or an Affiliate to terminate (i) the employment of an Employee with or without notice and with or without cause, (ii) the service of a Consultant pursuant to the
terms of such Consultant’s agreement with the Company or an Affiliate, or (iii) the service of a Director pursuant to the bylaws of the Company or an Affiliate, and any applicable provisions of the corporate law of the state in which the
Company or the Affiliate is incorporated, as the case may be. 

(e)        Change in Time Commitment. In the event a Participant’s regular
level of time commitment in the performance of his or her services for the Company and any Affiliates is reduced (for example, and without limitation, if the Participant is an Employee of the Company and the Employee has a change in status from a
full-time Employee to a part-time Employee) after the date of grant of any Stock Award to the Participant, the Board has the right in its sole discretion to (x) make a corresponding reduction in the number of shares subject to any portion of
such Stock Award that is scheduled to vest or become payable after the date of such change in time commitment, and (y) in lieu of or in combination with such a reduction, extend the vesting or payment schedule applicable to such Stock Award. In
the event of any such reduction, the Participant will have no right with respect to any portion of the Stock Award that is so reduced or extended. 

(f)        Incentive Stock Option Limitations. To the extent that the aggregate
Fair Market Value (determined at the time of grant) of Common Stock with respect to which Incentive Stock Options are exercisable for the first time by any Optionholder during any calendar year (under all plans of the Company and any Affiliates)
exceeds one hundred thousand dollars ($100,000) (or such other limit established in the Code) or otherwise does not comply with the rules governing Incentive Stock Options, the Options or portions thereof that exceed such limit (according to
the order in which they were granted) or otherwise do not comply with such rules will be treated as 

  
 14. 













 
Nonstatutory Stock Options, notwithstanding any contrary provision of the applicable Option Agreement(s). 

(g)        Investment Assurances. The Company may require a Participant, as a
condition of exercising or acquiring Common Stock under any Stock Award, (i) to give written assurances satisfactory to the Company as to the Participant’s knowledge and experience in financial and business matters and/or to employ a
purchaser representative reasonably satisfactory to the Company who is knowledgeable and experienced in financial and business matters and that he or she is capable of evaluating, alone or together with the purchaser representative, the merits and
risks of exercising the Stock Award; and (ii) to give written assurances satisfactory to the Company stating that the Participant is acquiring Common Stock subject to the Stock Award for the Participant’s own account and not with any
present intention of selling or otherwise distributing the Common Stock. The foregoing requirements, and any assurances given pursuant to such requirements, will be inoperative if (A) the issuance of the shares upon the exercise or acquisition
of Common Stock under the Stock Award has been registered under a then currently effective registration statement under the Securities Act, or (B) as to any particular requirement, a determination is made by counsel for the Company that such
requirement need not be met in the circumstances under the then applicable securities laws. The Company may, upon advice of counsel to the Company, place legends on stock certificates issued under the Plan as such counsel deems necessary or
appropriate in order to comply with applicable securities laws, including, but not limited to, legends restricting the transfer of the Common Stock. 

(h)        Withholding Obligations. Unless prohibited by the terms of a
Stock Award Agreement, the Company may, in its sole discretion, satisfy any federal, state or local tax withholding obligation relating to a Stock Award by any of the following means or by a combination of such means: (i) causing the
Participant to tender a cash payment; (ii) withholding shares of Common Stock from the shares of Common Stock issued or otherwise issuable to the Participant in connection with the Stock Award; provided, however, that no shares of Common
Stock are withheld with a value exceeding the minimum amount of tax required to be withheld by law (or such lesser amount as may be necessary to avoid classification of the Stock Award as a liability for financial accounting purposes);
(iii) withholding cash from a Stock Award settled in cash; (iv) withholding payment from any amounts otherwise payable to the Participant; or (v) by such other method as may be set forth in the Stock Award Agreement. 

(i)        Electronic Delivery. Any reference herein to a “written”
agreement or document will include any agreement or document delivered electronically or posted on the Company’s intranet (or other shared electronic medium controlled by the Company to which the Participant has access). 

(j)        Deferrals. To the extent permitted by applicable law, the Board, in
its sole discretion, may determine that the delivery of Common Stock or the payment of cash, upon the exercise, vesting or settlement of all or a portion of any Stock Award may be deferred and may establish programs and procedures for deferral
elections to be made by Participants. Deferrals by Participants will be made in accordance with Section 409A of the Code. Consistent with Section 409A of the Code, the Board may provide for distributions while a Participant is still an
employee 

  
 15. 













 
or otherwise providing services to the Company. The Board is authorized to make deferrals of Stock Awards and determine when, and in what annual percentages, Participants may receive payments,
including lump sum payments, following the Participant’s termination of Continuous Service, and implement such other terms and conditions consistent with the provisions of the Plan and in accordance with applicable law. 

(k)        Compliance with Section 409A of the Code. To the
extent that the Board determines that any Stock Award granted hereunder is subject to Section 409A of the Code, the Stock Award Agreement evidencing such Stock Award shall incorporate the terms and conditions necessary to avoid the consequences
specified in Section 409A(a)(1) of the Code. To the extent applicable, the Plan and Stock Award Agreements shall be interpreted in accordance with Section 409A of the Code. 

(l)        Repurchase Limitation. The terms of any repurchase right will
be specified in the Stock Award Agreement. The repurchase price for vested shares of Common Stock will be the Fair Market Value of the shares of Common Stock on the date of repurchase. The repurchase price for unvested shares of Common Stock will be
the lower of (i) the Fair Market Value of the shares of Common Stock on the date of repurchase or (ii) their original purchase price. However, the Company will not exercise its repurchase right until at least six (6) months (or
such longer or shorter period of time necessary to avoid classification of the Stock Award as a liability for financial accounting purposes) have elapsed following delivery of shares of Common Stock subject to the Stock Award, unless otherwise
specifically provided by the Board. 
 9.          ADJUSTMENTS UPON
CHANGES IN COMMON STOCK; OTHER CORPORATE EVENTS. 

(a)        Capitalization Adjustments. 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 that may be
issued pursuant to the exercise of Incentive Stock Options pursuant to Section 3(c), and (iii) the class(es) and number of securities and price per share of stock subject to outstanding Stock Awards. The Board will make such adjustments,
and its determination will be final, binding and conclusive. 

(b)        Dissolution or Liquidation. Except as otherwise provided in
the Stock Award Agreement, in the event of a dissolution or liquidation of the Company, all outstanding Stock Awards (other than Stock Awards consisting of vested and outstanding shares of Common Stock not subject to a forfeiture condition or the
Company’s right of repurchase) will terminate immediately prior to the completion of such dissolution or liquidation, and the shares of Common Stock subject to the Company’s repurchase rights or subject to a forfeiture condition may be
repurchased or reacquired by the Company notwithstanding the fact that the holder of such Stock Award is providing Continuous Service, provided, however, that the Board may, in its sole discretion, cause some or all Stock Awards to become
fully vested, exercisable and/or no longer subject to repurchase or forfeiture (to the extent such Stock Awards have not previously expired or terminated) before the dissolution or liquidation is completed but contingent on its completion. 

  
 16. 













 (c)         Corporate
Transactions. The following provisions will apply to Stock Awards in the event of a Transaction unless otherwise provided in the Stock Award Agreement or any other written agreement between the Company or any Affiliate and the Participant or
unless otherwise expressly provided by the Board at the time of grant of a Stock Award. In the event of a Transaction, then, notwithstanding any other provision of the Plan, the Board may take one or more of the following actions with respect to
Stock Awards, contingent upon the closing or completion of the Transaction: 

(i)        arrange for the surviving corporation or acquiring corporation (or
the surviving or acquiring corporation’s parent company) to assume or continue the Stock Award or to substitute a similar stock award for the Stock Award (including, but not limited to, an award to acquire the same consideration paid to the
stockholders of the Company pursuant to the Transaction); 

(ii)        arrange for the assignment of any reacquisition or repurchase
rights held by the Company in respect of Common Stock issued pursuant to the Stock Award to the surviving corporation or acquiring corporation (or the surviving or acquiring corporation’s parent company); 

(iii)        accelerate the vesting, in whole or in part, of the Stock Award
(and, if applicable, the time at which the Stock Award may be exercised) to a date prior to the effective time of such Transaction as the Board determines (or, if the Board does not determine such a date, to the date that is five (5) days
prior to the effective date of the Transaction), with such Stock Award terminating if not exercised (if applicable) at or prior to the effective time of the Transaction; provided, however, that the Board may require Participants to complete and
deliver to the Company a notice of exercise before the effective date of a Transaction, which exercise is contingent upon the effectiveness of such Transaction; 

(iv)        arrange for the lapse, in whole or in part, of any reacquisition
or repurchase rights held by the Company with respect to the Stock Award; 

(v)        cancel or arrange for the cancellation of the Stock Award, to the
extent not vested or not exercised prior to the effective time of the Transaction, in exchange for such cash consideration, if any, as the Board, in its sole discretion, may consider appropriate; and 

(vi)        make a payment, in such form as may be determined by the Board
equal to the excess, if any, of (A) the value of the property the Participant would have received upon the exercise of the Stock Award immediately prior to the effective time of the Transaction, over (B) any exercise price payable by such
holder in connection with such exercise. For clarity, this payment may be zero ($0) if the value of the property is equal to or less than the exercise price. Payments under this provision may be delayed to the same extent that payment of
consideration to the holders of the Company’s Common Stock in connection with the Transaction is delayed as a result of escrows, earn outs, holdbacks or any other contingencies. 

The Board need not take the same action or actions with respect to all Stock Awards or portions thereof or with respect to all Participants.
The Board may take different actions with respect to the vested and unvested portions of a Stock Award.  

  
 17. 













 (d)        Change in Control.
A Stock Award may be subject to additional acceleration of vesting and exercisability upon or after a Change in Control as may be provided in the Stock Award Agreement for such Stock Award or as may be provided in any other written agreement between
the Company or any Affiliate and the Participant, but in the absence of such provision, no such acceleration will occur. 

10.        PLAN TERM; EARLIER TERMINATION
OR SUSPENSION OF THE PLAN. 

(a)        Plan Term. The Board may suspend or terminate the Plan at any time.
Unless terminated sooner by the Board, the Plan will automatically terminate on the day before the tenth (10th) anniversary of the earlier of (i) the date the Plan is adopted by the Board, or (ii) the date the Plan is approved by the
stockholders of the Company. No Stock Awards may be granted under the Plan while the Plan is suspended or after it is terminated. 

(b)        No Impairment of Rights. Suspension or termination of the Plan will
not impair rights and obligations under any Stock Award granted while the Plan is in effect except with the written consent of the affected Participant or as otherwise permitted in the Plan. 

11.        EFFECTIVE DATE OF PLAN. 

This Plan will become effective on the Effective Date.  

12.        CHOICE OF LAW. 

The laws of the State of California will govern all questions concerning the construction, validity and interpretation
of this Plan, without regard to that state’s conflict of laws rules. 

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

(a)        “Affiliate” means, at the time of
determination, any “parent” or “majority-owned subsidiary” of the Company, as such terms are defined in Rule 405. The Board will have the authority to determine the time or times at which “parent” or
“majority-owned subsidiary” status is determined within the foregoing definition. 

(b)        “Board” means the Board of Directors of the
Company. 
 (c)        “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 Stock Award after the Effective Date 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, reverse stock split, liquidating dividend, combination of shares, exchange of
shares, change in corporate structure, or any similar equity restructuring transaction, as that term is used in Statement of Financial Accounting Standards Board Accounting Standards Codification Topic 718 (or any successor


  
 18. 













 
thereto). Notwithstanding the foregoing, the conversion of any convertible securities of the Company will not be treated as a Capitalization Adjustment. 

(d)        “Cause” will have the meaning
ascribed to such term in any written agreement between the Participant and the Company defining such term and, in the absence of such agreement, such term means with respect to a Participant, the occurrence of any of the following
events: (i) such Participant’s commission of any felony or any crime involving fraud, dishonesty or moral turpitude under the laws of the United States or any state thereof; (ii) such Participant’s attempted commission of, or
participation in, a fraud or material act of dishonesty against the Company; (iii) such Participant’s intentional, material violation of any contract or agreement between the Participant and the Company or of any statutory duty owed to the
Company; (iv) such Participant’s repeated and willful failure to satisfactorily perform such Participant’s job duties after 30 days written notice of such deficiency and an opportunity to cure (of at least 15 business days); (v) such
Participant’s engaging or participating in any activity which is directly competitive with or injurious to the Company or which violates any material provisions of such Participant’s Proprietary Information and Inventions Agreement
with the Company (if applicable) which remains uncured after 30 days written notice thereof; or (vi) such Participant’s gross misconduct. The determination that a termination of the Participant’s Continuous Service is either for Cause
or without Cause will be made by the Company in its sole discretion. Any determination by the Company that the Continuous Service of a Participant was terminated with or without Cause for the purposes of outstanding Stock Awards held by such
Participant will have no effect upon any determination of the rights or obligations of the Company or such Participant for any other purpose. 

(e)        “Change in Control” means the occurrence, in
a single transaction or in a series of related transactions, of any one or more of the following events: 

(i)        any Exchange Act Person becomes the Owner, directly or indirectly,
of securities of the Company representing more than fifty percent (50%) of the combined voting power of the Company’s then outstanding securities other than by virtue of a merger, consolidation or similar transaction. Notwithstanding
the foregoing, a Change in Control will not be deemed to occur (A) on account of the acquisition of securities of the Company directly from the Company, (B) on account of the acquisition of securities of the Company by an investor, any
affiliate thereof or any other Exchange Act Person that acquires the Company’s securities in a transaction or series of related transactions the primary purpose of which is to obtain financing for the Company through the issuance of equity
securities or (C) solely because the level of Ownership held by any Exchange Act Person (the “Subject Person”) exceeds the designated percentage threshold of the outstanding voting
securities as a result of a repurchase or other acquisition of voting securities by the Company reducing the number of shares outstanding, provided that if a Change in Control would occur (but for the operation of this sentence) as a result of the
acquisition of voting securities by the Company, and after such share acquisition, the Subject Person becomes the Owner of any additional voting securities that, assuming the repurchase or other acquisition had not occurred, increases the percentage
of the then outstanding voting securities Owned by the Subject Person over the designated percentage threshold, then a Change in Control will be deemed to occur;  

  
 19. 













 (ii)        there is
consummated a merger, consolidation or similar transaction involving (directly or indirectly) the Company and, immediately after the consummation of such merger, consolidation or similar transaction, the stockholders of the Company immediately prior
thereto do not Own, directly or indirectly, either (A) outstanding voting securities representing more than fifty percent (50%) of the combined outstanding voting power of the surviving Entity in such merger, consolidation or similar
transaction or (B) more than fifty percent (50%) of the combined outstanding voting power of the parent of the surviving Entity in such merger, consolidation or similar transaction, in each case in substantially the same proportions
as their Ownership of the outstanding voting securities of the Company immediately prior to such transaction; 

(iii)        the stockholders of the Company approve or the Board approves a
plan of complete dissolution or liquidation of the Company, or a complete dissolution or liquidation of the Company will otherwise occur, except for a liquidation into a parent corporation; or 

(iv)        there is consummated a sale, lease, exclusive license or other
disposition of all or substantially all of the consolidated assets of the Company and its Subsidiaries, other than a sale, lease, license or other disposition of all or substantially all of the consolidated assets of the Company and its Subsidiaries
to an Entity, more than fifty percent (50%) of the combined voting power of the voting securities of which are Owned by stockholders of the Company in substantially the same proportions as their Ownership of the outstanding voting
securities of the Company immediately prior to such sale, lease, license or other disposition. 
 Notwithstanding the
foregoing definition or any other provision of this Plan, (A) the term Change in Control will not include a sale of assets, merger or other transaction effected exclusively for the purpose of changing the domicile of the Company, and
(B) the definition of Change in Control (or any analogous term) in an individual written agreement between the Company or any Affiliate and the Participant will supersede the foregoing definition with respect to Stock Awards subject to such
agreement; provided, however, that if no definition of Change in Control or any analogous term is set forth in such an individual written agreement, the foregoing definition will apply. 

(f)        “Code” means the Internal Revenue Code of
1986, as amended, including any applicable regulations and guidance thereunder. 

(g)        “Committee” means a committee of one
(1) or more Directors to whom authority has been delegated by the Board in accordance with Section 2(c). 

(h)        “Common Stock” means the common stock of the
Company. 
 (i)        “Company” means Synthorx,
Inc., a Delaware corporation. 

(j)        “Consultant” means any person, including an
advisor, who (i) provides consulting or advisory services to the Company or to a parent or subsidiary of the Company either (a) directly, in an individual capacity, or (b) indirectly, through an entity of which such person is an
employee, consultant, partner or member and which entity provides to the Company or to a parent or 

  
 20. 













 
subsidiary of the Company consulting services involving such individual, or (ii) serving as a member of the board of directors of an Affiliate and is compensated for such services. However,
service solely as a Director, or payment of a fee for such service, will not cause a Director to be considered a “Consultant” for purposes of the Plan.  

(k)        “Continuous Service” means that the
Participant’s service with the Company and/or an Affiliate, whether as an Employee, Director or Consultant, is not interrupted or terminated. A change in the capacity in which the Participant renders service to the Company or an Affiliate as an
Employee, Director or Consultant or a change in the Entity for which the Participant renders such service, provided that there is no interruption or termination of the Participant’s service with the Company or an Affiliate, will not terminate a
Participant’s Continuous Service; provided, however, that if the Entity for which a Participant is rendering services ceases to qualify as an Affiliate, as determined by the Board in its sole discretion, such Participant’s
Continuous Service will be considered to have terminated on the date such Entity ceases to qualify as an Affiliate. For example, a change in status from an Employee of the Company to a Consultant of an Affiliate or to a Director will not constitute
an interruption of Continuous Service. To the extent permitted by law, the Board or the chief executive officer of the Company, in that party’s sole discretion, may determine whether Continuous Service will be considered interrupted in the case
of (i) any leave of absence approved by the Board or chief executive officer, including sick leave, military leave or any other personal leave, or (ii) transfers between the Company, an Affiliate, or their successors. Notwithstanding the
foregoing, a leave of absence will be treated as Continuous Service for purposes of vesting in a Stock Award only to such extent as may be provided in the Company’s leave of absence policy, in the written terms of any leave of absence agreement
or policy applicable to the Participant, or as otherwise required by law. 

(l)        “Corporate Transaction” means the
occurrence, in a single transaction or in a series of related transactions, of any one or more of the following events: 

(i)        the consummation of a sale or other disposition of all or
substantially all, as determined by the Board in its sole discretion, of the consolidated assets of the Company and its Subsidiaries; 

(ii)        the consummation of a sale or other disposition of at least
ninety percent (90%) of the outstanding securities of the Company; 

(iii)        the consummation of a merger, consolidation or similar
transaction following which the Company is not the surviving corporation; or 

(iv)        the consummation of a merger, consolidation or similar transaction
following which the Company is the surviving corporation but the shares of Common Stock outstanding immediately preceding the merger, consolidation or similar transaction are converted or exchanged by virtue of the merger, consolidation or similar
transaction into other property, whether in the form of securities, cash or otherwise. 

(m)        “Director” means a member of the Board. 


  
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(n)        “Disability” means, with respect to a
Participant, the inability of such Participant to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment that can be expected to result in death or that has lasted or can be expected to last
for a continuous period of not less than twelve (12) months as provided in Sections 22(e)(3) and 409A(a)(2)(c)(i) of the Code, and will be determined by the Board on the basis of such medical evidence as the Board deems warranted
under the circumstances. 
 (o)        “Effective
Date” means the effective date of this Plan, which is the earlier of (i) the date that this Plan is first approved by the Company’s stockholders, and (ii) the date this Plan is adopted by the Board. 

(p)        “Employee” means any person employed by the
Company or an Affiliate. 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. 

(q)        “Entity” means a corporation, partnership,
limited liability company or other entity. 
 (r)        “Exchange
Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder. 

(s)        “Exchange Act Person” means
any natural person, Entity or “group” (within the meaning of Section 13(d) or 14(d) of the Exchange Act), except that “Exchange Act Person” will not include (i) the Company or any Subsidiary of the Company,
(ii) any employee benefit plan of the Company or any Subsidiary of the Company or any trustee or other fiduciary holding securities under an employee benefit plan of the Company or any Subsidiary of the Company, (iii) an underwriter
temporarily holding securities pursuant to an offering of such securities, (iv) an Entity Owned, directly or indirectly, by the stockholders of the Company in substantially the same proportions as their Ownership of stock of the Company; or
(v) any natural person, Entity or “group” (within the meaning of Section 13(d) or 14(d) of the Exchange Act) that, as of the Effective Date, is the Owner, directly or indirectly, of securities of the Company representing more
than fifty percent (50%) of the combined voting power of the Company’s then outstanding securities. 

(t)        “Fair Market Value” means, as of any date,
the value of the Common Stock determined by the Board in compliance with Section 409A of the Code or, in the case of an Incentive Stock Option, in compliance with Section 422 of the Code. 

(u)        “Incentive Stock Option” means an option
granted pursuant to Section 5 of the Plan that is intended to be, and that qualifies as, an “incentive stock option” within the meaning of Section 422 of the Code. 

(v)        “Nonstatutory Stock Option” means any option
granted pursuant to Section 5 of the Plan that does not qualify as an Incentive Stock Option. 

(w)        “Officer” means any person designated by the
Company as an officer. 

  
 22. 














(x)        “Option” means an Incentive Stock Option or a
Nonstatutory Stock Option to purchase shares of Common Stock granted pursuant to the Plan. 

(y)        “Option Agreement” means a written agreement
between the Company and an Optionholder evidencing the terms and conditions of an Option grant. Each Option Agreement will be subject to the terms and conditions of the Plan. 

(z)        “Optionholder” means a person to whom an
Option is granted pursuant to the Plan or, if applicable, such other person who holds an outstanding Option. 

(aa)        “Other Stock Award” means an award based in
whole or in part by reference to the Common Stock which is granted pursuant to the terms and conditions of Section 6(c). 

(bb)        “Other Stock Award Agreement” means a
written agreement between the Company and a holder of an Other Stock Award evidencing the terms and conditions of an Other Stock Award grant. Each Other Stock Award Agreement will be subject to the terms and conditions of the Plan. 

(cc)        “Own,” “Owned,”
“Owner,” “Ownership” A person or Entity will be deemed to “Own,” to have “Owned,” to be the “Owner” of, or to have acquired “Ownership” of securities if
such person or Entity, directly or indirectly, through any contract, arrangement, understanding, relationship or otherwise, has or shares voting power, which includes the power to vote or to direct the voting, with respect to such securities. 

(dd)        “Participant” means a person to whom a
Stock Award is granted pursuant to the Plan or, if applicable, such other person who holds an outstanding Stock Award. 

(ee)        “Plan” means this Synthorx, Inc. 2014
Equity Incentive Plan. 
 (ff)        “Restricted Stock
Award” means an award of shares of Common Stock which is granted pursuant to the terms and conditions of Section 6(a). 

(gg)        “Restricted Stock Award Agreement” means a
written agreement between the Company and a holder of a Restricted Stock Award evidencing the terms and conditions of a Restricted Stock Award grant. Each Restricted Stock Award Agreement will be subject to the terms and conditions of the Plan. 

(hh)        “Restricted Stock Unit Award”
means a right to receive shares of Common Stock which is granted pursuant to the terms and conditions of Section 6(b). 

(ii)        “Restricted Stock Unit Award
Agreement” means a written agreement between the Company and a holder of a Restricted Stock Unit Award evidencing the terms and conditions of a Restricted Stock Unit Award grant. Each Restricted Stock Unit Award Agreement
will be subject to the terms and conditions of the Plan. 

(jj)        “Rule 405” means Rule 405 promulgated under
the Securities Act. 

  
 23. 













 (kk)        “Rule
701” means Rule 701 promulgated under the Securities Act. 

(ll)        “Securities Act” means the Securities Act
of 1933, as amended. 
 (mm)        “Stock Appreciation
Right” or “SAR” means a right to receive the appreciation on Common Stock that is granted pursuant to the terms and conditions of Section 5. 

(nn)        “Stock Appreciation Right Agreement” means
a written agreement between the Company and a holder of a Stock Appreciation Right evidencing the terms and conditions of a Stock Appreciation Right grant. Each Stock Appreciation Right Agreement will be subject to the terms and conditions of the
Plan. 
 (oo)        “Stock Award” means any right to
receive Common Stock granted under the Plan, including an Incentive Stock Option, a Nonstatutory Stock Option, a Restricted Stock Award, a Restricted Stock Unit Award, a Stock Appreciation Right or any Other Stock Award. 

(pp)        “Stock Award Agreement” means a written
agreement between the Company and a Participant evidencing the terms and conditions of a Stock Award grant. Each Stock Award Agreement will be subject to the terms and conditions of the Plan. 

(qq)        “Subsidiary” means, with respect to the
Company, (i) any corporation of which more than fifty percent (50%) of the outstanding capital stock having ordinary voting power to elect a majority of the board of directors of such corporation (irrespective of whether, at the time,
stock of any other class or classes of such corporation will have or might have voting power by reason of the happening of any contingency) is at the time, directly or indirectly, Owned by the Company, and (ii) any partnership, limited
liability company or other entity in which the Company has a direct or indirect interest (whether in the form of voting or participation in profits or capital contribution) of more than fifty percent (50%). 

(rr)        “Ten Percent Stockholder” means a person
who Owns (or is deemed to Own pursuant to Section 424(d) of the Code) stock possessing more than ten percent (10%) of the total combined voting power of all classes of stock of the Company or any Affiliate. 

(ss)         “Transaction” means a Corporate
Transaction or a Change in Control. 

  
 24. 













 SYNTHORX, INC. 

STOCK OPTION GRANT NOTICE 

(2014 EQUITY INCENTIVE PLAN) 

Synthorx, Inc. (the “Company”), pursuant to its 2014 Equity Incentive Plan (the
“Plan”), hereby grants to Optionholder an option to purchase the number of shares of the Company’s Common Stock set forth below. This option is subject to all of the terms and conditions as set forth in this notice, in
the Option Agreement, the Plan and the Notice of Exercise, all of which are attached hereto and incorporated herein in their entirety. Capitalized terms not explicitly defined herein but defined in the Plan or the Option Agreement will have the same
definitions as in the Plan or the Option Agreement. If there is any conflict between the terms in this notice and the Plan, the terms of the Plan will control. 
  

			
	 Optionholder:
	  	                                      
  
	 Date of Grant:
	  	                                      
  
	 Vesting Commencement Date:
	  	                                      
  
	 Number of Shares Subject to Option:
	  	                                      
  
	 Exercise Price (Per Share):
	  	$                                      

	 Total Exercise Price:
	  	$                                      

	 Expiration Date:
	  	                                      
  

  

									
	 Type of Grant:
	  	 ☐
	  	 Incentive Stock Option1
	  	 ☐
	  	 Nonstatutory Stock Option

					
	 Exercise Schedule:
	  	 ☐
	  	 Same as Vesting Schedule
	  	 ☐
	  	 Early Exercise Permitted

		
	 Vesting Schedule:
	  	 [To be determined by the Board, but in any event, subject to the Optionholder’s Continuous Service as of
each such date.]

		
	 Payment:
	  	 By one or a combination of the following items (described in the Option Agreement):

			
		  	 ☒
	  	 By cash, check, bank draft or money order payable to the Company

		  	 ☐
	  	 Pursuant to a Regulation T Program if the shares are publicly traded

		  	 ☐
	  	 By delivery of already-owned shares if the shares are publicly traded

		  	 ☐
	  	 If and only to the extent this option is a Nonstatutory Stock Option, and subject to the

		  	 Company’s consent at the time of exercise, by a “net exercise” arrangement


 Additional Terms/Acknowledgements: Optionholder acknowledges receipt of, and understands and agrees to,
this Stock Option Grant Notice, the Option Agreement and the Plan. Optionholder acknowledges and agrees that this Stock Option Grant Notice and the Option Agreement may not be modified, amended or revised except as provided in the Plan.
Optionholder further acknowledges that as of the Date of Grant, this Stock Option Grant Notice, the Option Agreement, and the Plan set forth the entire understanding between Optionholder and the Company regarding the Optionholder’s
acquisition of common stock of the Company and supersede all prior oral and written agreements, promises and/or representations on that subject with the exception of (i) options previously granted and delivered to Optionholder, (ii) any
written employment or severance arrangement that would provide for vesting acceleration of this option upon the terms and conditions set forth therein and (iii) the following agreements: 

 

			
	                OTHER AGREEMENTS:	  	
                       
                                         



  

 
 1 If this is an Incentive Stock Option, it (plus other outstanding Incentive Stock Options) cannot be first exercisable for more than $100,000 in value (measured by exercise price) in any
calendar year. Any excess over $100,000 is a Nonstatutory Stock Option. 













			
		  	
                       
                                         



 By accepting this option, Optionholder consents to receive such documents by electronic delivery and to
participate in the Plan through an on-line or electronic system established and maintained by the Company or another third party designated by the Company. 

 

					
	SYNTHORX, INC.	  		  	OPTIONHOLDER:
			
	
By:                      
                                         
     
	  		  	
                       
                                         
          

	Signature	  		  	Signature
			
	
Title:                      
                                         
  
	  		  	
Date:                      
                                         
  

			
	
Date:                      
                                         
  
	  		  	

 ATTACHMENTS: Option Agreement, 2014 Equity Incentive Plan and Notice of
Exercise 












 ATTACHMENT I 

OPTION AGREEMENT 












 SYNTHORX, INC. 

2014 EQUITY INCENTIVE PLAN 

OPTION AGREEMENT 

(INCENTIVE STOCK OPTION OR NONSTATUTORY STOCK
OPTION) 
 Pursuant to your Stock Option Grant Notice (“Grant Notice”) and this
Option Agreement, Synthorx, Inc. (the “Company”) has granted you an option under its 2014 Equity Incentive Plan (the “Plan”) to purchase the number of shares of the Company’s Common
Stock (the “Common Stock”) indicated in your Grant Notice at the exercise price indicated in your Grant Notice. The option is granted to you effective as of the date of grant set forth in the Grant Notice (the
“Date of Grant”). If there is any conflict between the terms in this Option Agreement and the Plan, the terms of the Plan will control. Capitalized terms not explicitly defined in this Option Agreement or in the Grant Notice
but defined in the Plan will have the same definitions as in the Plan. 
 The details of your option, in addition to those
set forth in the Grant Notice and the Plan, are as follows: 

1.        VESTING. 

  (a)        Your option will vest as provided in your Grant Notice.
Vesting will cease upon the termination of your Continuous Service. 

  (b)        If a Change in Control occurs and within one
(1) month prior to, or within twelve (12) months after, the effective time of such Change in Control, your Continuous Service terminates due to an involuntary termination (not including death or Disability) without Cause or due to your
voluntary termination with Good Reason, then, as of the date of termination of Continuous Service, the vesting and exercisability of the option will be accelerated in full. 

  (c)        “Good Reason” means the
occurrence of any of the following events, conditions or actions taken by the Company without your written consent: (i) a material reduction of your annual base salary; provided, however, that Good Reason shall not be deemed to have
occurred in the event of a reduction in your annual base salary that is pursuant to a salary reduction program affecting substantially all of the similarly situated employees of the Company and that does not adversely affect you to a greater extent
than other similarly situated employees; (ii) a material reduction in your authority, duties or responsibilities; (iii) a relocation of your principal place of employment with the Company to a place that increases your one-way commute by more than fifty (50) miles as compared to your then-current principal place of employment immediately prior to such relocation (excluding regular travel in the ordinary course of business);
or (iv) a material breach by the Company of any provision of this Option Agreement or your employment agreement with the Company; provided, however, that in each case above, in order for your resignation to be deemed to have been for
Good Reason, you must first give the Board written notice of the action or omission giving rise to “Good Reason” within thirty (30) days after the first occurrence thereof; the Company must fail to reasonably cure such action or
omission within thirty (30) days after receipt of such notice (the “Cure Period”), and your resignation from all positions 

  
 1 













 
you hold with the Company must be effective not later than thirty (30) days after the expiration of such Cure Period. 

2.        NUMBER OF SHARES
AND EXERCISE PRICE. The number of shares of Common Stock subject to your option and your exercise price per share in your Grant Notice will be adjusted for Capitalization Adjustments. 

3.        EXERCISE RESTRICTION
FOR NON-EXEMPT EMPLOYEES. If you are an Employee eligible for overtime compensation under the Fair Labor Standards Act of 1938, as amended (that
is, a “Non-Exempt Employee”), and except as otherwise provided in the Plan, you may not exercise your option until you have completed at least six (6) months of Continuous Service
measured from the Date of Grant, even if you have already been an employee for more than six (6) months. Consistent with the provisions of the Worker Economic Opportunity Act, you may exercise your option as to any vested portion prior to such
six (6) month anniversary in the case of (i) your death or disability, (ii) a Corporate Transaction in which your option is not assumed, continued or substituted, (iii) a Change in Control or (iv) your termination of
Continuous Service on your “retirement” (as defined in the Company’s benefit plans). 

4.        EXERCISE PRIOR TO
VESTING (“EARLY EXERCISE”). If permitted in your Grant Notice (i.e., the “Exercise Schedule” indicates “Early Exercise Permitted”) and
subject to the provisions of your option, you may elect at any time that is both (i) during the period of your Continuous Service and (ii) during the term of your option, to exercise all or part of your option, including the unvested
portion of your option; provided, however, that: 

  (a)        a partial exercise of your option will be deemed to
cover first vested shares of Common Stock and then the earliest vesting installment of unvested shares of Common Stock; 

  (b)        any shares of Common Stock so purchased from
installments that have not vested as of the date of exercise will be subject to the purchase option in favor of the Company as described in the Company’s form of Early Exercise Stock Purchase Agreement; 

  (c)        you will enter into the Company’s form of Early
Exercise Stock Purchase Agreement with a vesting schedule that will result in the same vesting as if no early exercise had occurred; and 

  (d)        if your option is an Incentive Stock Option, then, to
the extent that the aggregate Fair Market Value (determined at the Date of Grant) of the shares of Common Stock with respect to which your option plus all other Incentive Stock Options you hold are exercisable for the first time by you during any
calendar year (under all plans of the Company and its Affiliates) exceeds one hundred thousand dollars ($100,000), your option(s) or portions thereof that exceed such limit (according to the order in which they were granted) will be treated as
Nonstatutory Stock Options. 
 5.        METHOD
OF PAYMENT. You must pay the full amount of the exercise price for the shares you wish to exercise. You may pay the exercise price in cash or by check, bank draft or money order payable to the Company or in any
other manner permitted by your Grant Notice, which may include one or more of the following: 

  
 2 














  (a)        Provided that at the time of exercise the Common Stock
is publicly traded, pursuant to a program developed under Regulation T as promulgated by the Federal Reserve Board that, prior to the issuance of Common Stock, results in either the receipt of cash (or check) by the Company or the receipt of
irrevocable instructions to pay the aggregate exercise price to the Company from the sales proceeds. This manner of payment is also known as a “broker-assisted exercise”, “same day sale”, or “sell to cover”. 

  (b)        Provided that at the time of exercise the Common Stock
is publicly traded, by delivery to the Company (either by actual delivery or attestation) of already-owned shares of Common Stock that are owned free and clear of any liens, claims, encumbrances or security interests, and that are valued at Fair
Market Value on the date of exercise. “Delivery” for these purposes, in the sole discretion of the Company at the time you exercise your option, will include delivery to the Company of your attestation of ownership of such shares of Common
Stock in a form approved by the Company. You may not exercise your option by delivery to the Company of Common Stock if doing so would violate the provisions of any law, regulation or agreement restricting the redemption of the Company’s stock.

   (c)        If this option is a Nonstatutory Stock Option,
subject to the consent of the Company at the time of exercise, by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Common Stock issued upon exercise of your option by the largest whole number
of shares with a Fair Market Value that does not exceed the aggregate exercise price. You must pay any remaining balance of the aggregate exercise price not satisfied by the “net exercise” in cash or other permitted form of payment. Shares
of Common Stock will no longer be outstanding under your option and will not be exercisable thereafter if those shares (i) are used to pay the exercise price pursuant to the “net exercise,” (ii) are delivered to you as a result of
such exercise, and (iii) are withheld to satisfy your tax withholding obligations. 

  (d)        Pursuant to the following deferred payment alternative:

       (i)        Not less than one hundred
percent (100%) of the aggregate exercise price, plus accrued interest, will be due four (4) years from date of exercise or, at the Company’s election, upon termination of your Continuous Service. 

      (ii)        Interest will be compounded at
least annually and will be charged at the minimum rate of interest necessary to avoid (1) the treatment as interest, under any applicable provisions of the Code, of any amounts other than amounts stated to be interest under the deferred payment
arrangement and (2) the classification of your option as a liability for financial accounting purposes. 

      (iii)        In order to elect the
deferred payment alternative, you must, as a part of your written notice of exercise, give notice of the election of this payment alternative and, in order to secure the payment of the deferred exercise price to the Company hereunder, if the Company
so requests, you must tender to the Company a promissory note and a pledge agreement covering the purchased shares of Common Stock, both in form and substance satisfactory to the Company, or such other or additional documentation as the Company may
request. 

  
 3 














6.        WHOLE SHARES. You may exercise
your option only for whole shares of Common Stock. 

7.        SECURITIES LAW
COMPLIANCE. In no event may you exercise your option unless the shares of Common Stock issuable upon exercise are then registered under the Securities Act or, if not registered, the Company has determined that your exercise and
the issuance of the shares would be exempt from the registration requirements of the Securities Act. The exercise of your option also must comply with all other applicable laws and regulations governing your option, and you may not exercise your
option if the Company determines that such exercise would not be in material compliance with such laws and regulations (including any restrictions on exercise required for compliance with Treas. Reg.
1.401(k)-1(d)(3), if applicable). 

8.        TERM. You may not exercise your option before
the commencement or after the expiration of its term. The term of your option commences on the Date of Grant and expires, subject to the provisions of Section 5(h) of the Plan, upon the earliest of the following: 

  (a)        immediately upon the termination of your Continuous
Service for Cause; 
   (b)        three (3) months after the
termination of your Continuous Service for any reason other than Cause, Disability or death, provided that if during any part of such three (3) month period your option is not exercisable solely because of the condition set forth in the section
above relating to “Securities Law Compliance,” your option will not expire until the earlier of the Expiration Date or until it will have been exercisable for an aggregate period of three (3) months after the termination of your
Continuous Service; provided further, that if (i) you are a Non-Exempt Employee, (ii) your Continuous Service terminates within six (6) months after the Date of Grant, and (iii) you
have vested in a portion of your option at the time of your termination of Continuous Service, your option will not expire until the earlier of (x) the later of (A) the date that is seven (7) months after the Date of Grant, and
(B) the date that is three (3) months after the termination of your Continuous Service, and (y) the Expiration Date; 

  (c)        twelve (12) months after the termination of your
Continuous Service due to your Disability; 

  (d)        eighteen (18) months after your death if you die
during your Continuous Service; 
   (e)        the Expiration
Date indicated in your Grant Notice; or 
   (f)        the day
before the tenth (10th) anniversary of the Date of Grant. 
 Notwithstanding the foregoing, if you die during the period
provided in Section 8(b) or 8(c) above, the term of your option will not expire until the earlier of eighteen (18) months after your death, the Expiration Date indicated in your Grant Notice, or the day before the tenth (10th) anniversary of the Date of Grant. 
 If your option is an Incentive
Stock Option, note that to obtain the federal income tax advantages associated with an Incentive Stock Option, the Code requires that at all times beginning on the date of grant of your option and ending on the day three (3) months before the
date of your 

  
 4 













 
option’s exercise, you must be an employee of the Company or an Affiliate, except in the event of your death or Disability. The Company has provided for extended exercisability of your
option under certain circumstances for your benefit but cannot guarantee that your option will necessarily be treated as an Incentive Stock Option if you continue to provide services to the Company or an Affiliate as a Consultant or Director after
your employment terminates or if you otherwise exercise your option more than three (3) months after the date your employment with the Company or an Affiliate terminates. 

9.        EXERCISE. 

  (a)        You may exercise the vested portion of your option (and
the unvested portion of your option if your Grant Notice so permits) during its term by (i) delivering a Notice of Exercise (in a form designated by the Company) or completing such other documents and/or procedures designated by the Company for
exercise, and (ii) paying the exercise price and any applicable withholding taxes to the Company’s Secretary, stock plan administrator, or such other person as the Company may designate, together with such additional documents as the
Company may then require. As a condition to the Company’s issuance of any shares of Common Stock upon exercise hereof, the Company may require you to execute certain agreements between/among the Company and certain of its stockholders,
including, without limitation, a right of first refusal and co-sale agreement, a voting agreement and/or similar agreements. 

  (b)        By exercising your option you agree that, as a
condition to any exercise of your option, the Company may require you to enter into an arrangement providing for the payment by you to the Company of any tax withholding obligation of the Company arising by reason of (i) the exercise of your
option, (ii) the lapse of any substantial risk of forfeiture to which the shares of Common Stock are subject at the time of exercise, or (iii) the disposition of shares of Common Stock acquired upon such exercise. 

  (c)        If your option is an Incentive Stock Option, by
exercising your option you agree that you will notify the Company in writing within fifteen (15) days after the date of any disposition of any of the shares of the Common Stock issued upon exercise of your option that occurs within two
(2) years after the Date of Grant or within one (1) year after such shares of Common Stock are transferred upon exercise of your option. 

  (d)        By exercising your option you agree that you will not
sell, dispose of, transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar transaction with the same economic effect as a sale with respect to any shares of Common Stock or other securities of the
Company held by you, for a period of one hundred eighty (180) days following the effective date of a registration statement of the Company filed under the Securities Act or such longer period as the underwriters or the Company will request to
facilitate compliance with FINRA Rule 2711 or NYSE Member Rule 472 or any successor or similar rules or regulation (the “Lock-Up Period”); provided, however, that nothing
contained in this section will prevent the exercise of a repurchase option, if any, in favor of the Company during the Lock-Up Period. You further agree to execute and deliver such other agreements as may be
reasonably requested by the Company or the underwriters that are consistent with the foregoing or that are necessary to give further effect thereto. In order to enforce the foregoing covenant, the Company may impose stop-transfer instructions with
respect to your shares of Common Stock until the end 

  
 5 













 
of such period. You also agree that any transferee of any shares of Common Stock (or other securities) of the Company held by you will be bound by this Section 9(d). The underwriters of the
Company’s stock are intended third party beneficiaries of this Section 9(d) and will have the right, power and authority to enforce the provisions hereof as though they were a party hereto. 

10.        TRANSFERABILITY. Except as otherwise provided
in this Section 10, your option is not transferable, except by will or by the laws of descent and distribution, and is exercisable during your life only by you. 

  (a)        Certain Trusts. Upon receiving written
permission from the Board or its duly authorized designee, you may transfer your option to a trust if you are considered to be the sole beneficial owner (determined under Section 671 of the Code and applicable state law) while the option is
held in the trust. You and the trustee must enter into transfer and other agreements required by the Company. 

  (b)        Domestic Relations Orders. Upon receiving
written permission from the Board or its duly authorized designee, and provided that you and the designated transferee enter into transfer and other agreements required by the Company, you may transfer your option pursuant to the terms of a domestic
relations order, official marital settlement agreement or other divorce or separation instrument as permitted by Treasury Regulation 1.421-1(b)(2) that contains the information required by the Company to
effectuate the transfer. You are encouraged to discuss the proposed terms of any division of this option with the Company prior to finalizing the domestic relations order or marital settlement agreement to help ensure the required information is
contained within the domestic relations order or marital settlement agreement. If this option is an Incentive Stock Option, this option may be deemed to be a Nonstatutory Stock Option as a result of such transfer. 

  (c)        Beneficiary Designation. Upon receiving written
permission from the Board or its duly authorized designee, you may, by delivering written notice to the Company, in a form approved by the Company and any broker designated by the Company to handle option exercises, designate a third party who, on
your death, will thereafter be entitled to exercise this option and receive the Common Stock or other consideration resulting from such exercise. In the absence of such a designation, your executor or administrator of your estate will be entitled to
exercise this option and receive, on behalf of your estate, the Common Stock or other consideration resulting from such exercise. 

11.         CHANGE IN CONTROL.

 If any payment or benefit you would receive from the Company or otherwise in connection with a Change in Control or
other similar transaction (“Payment”) would (i) constitute a “parachute payment” within the meaning of Section 280G of the Code, and (ii) but for this sentence, be subject to the excise tax imposed by
Section 4999 of the Code (the “Excise Tax”), then such Payment will be equal to the Reduced Amount. The “Reduced Amount” will be either (x) the largest portion of the Payment that would result in no
portion of the Payment being subject to the Excise Tax, or (y) the largest portion, up to and including the total, of the Payment, whichever amount ((x) or (y)), after taking into account all applicable federal, state and local employment
taxes, income taxes, and the Excise Tax (all computed at the highest applicable 

  
 6 













 
marginal rate), results in your receipt of the greatest economic benefit notwithstanding that all or some portion of the Payment may be subject to the Excise Tax. If a Reduced Amount will give
rise to the greater after tax benefit, the reduction in the Payments will occur in the following order: (a) reduction of cash payments; (b) cancellation of accelerated vesting of equity awards other than stock options;
(c) cancellation of accelerated vesting of stock options; and (d) reduction of other benefits paid to you. Within any such category of payments and benefits (that is, (a), (b), (c) or (d)), a reduction will occur first with respect to
amounts that are not “deferred compensation” within the meaning of Section 409A of the Code and then with respect to amounts that are. In the event that acceleration of compensation from your equity awards is to be reduced, such
acceleration of vesting will be canceled, subject to the immediately preceding sentence, in the reverse order of the date of grant. 

The independent registered public accounting firm engaged by the Company for general audit purposes as of the day prior to the
effective date of the event described in Section 280G(b)(2)(A)(i) of the Code will perform the foregoing calculations. If the independent registered public accounting firm so engaged by the Company is serving as accountant or auditor for the
individual, entity or group effecting such event, the Company will appoint a nationally recognized independent registered public accounting firm to make the determinations required hereunder. The Company will bear all expenses with respect to the
determinations by such independent registered public accounting firm required to be made hereunder. The independent registered public accounting firm engaged to make the determinations hereunder will provide its calculations, together with detailed
supporting documentation, to the Company and you within thirty (30) calendar days after the date on which your right to a Payment is triggered (if requested at that time by the Company or you) or such other time as reasonably requested by the
Company or you. Any good faith determinations of the independent registered public accounting firm made hereunder will be final, binding and conclusive upon the Company and you. 

12.        RIGHT OF FIRST
REFUSAL. Shares of Common Stock that you acquire upon exercise of your option are subject to any right of first refusal that may be described in the Company’s bylaws in effect at such time the Company elects to exercise its
right; provided, however, that if your option is an Incentive Stock Option and the right of first refusal described in the Company’s bylaws in effect at the time the Company elects to exercise its right is more beneficial to you than the
right of first refusal described in the Company’s bylaws on the Date of Grant, then the right of first refusal described in the Company’s bylaws on the Date of Grant will apply. The Company’s right of first refusal will expire on the
first date upon which any security of the Company is listed (or approved for listing) upon notice of issuance on a national securities exchange or quotation system. 

13.        RIGHT OF
REPURCHASE. To the extent provided in the Company’s bylaws in effect at such time the Company elects to exercise its right, the Company will have the right to repurchase all or any part of the shares of Common Stock you
acquire pursuant to the exercise of your option. 

14.        OPTION NOT A
SERVICE CONTRACT. Your option is not an employment or service contract, and nothing in your option will be deemed to create in any way whatsoever any obligation on your part to continue in the employ of the Company
or an Affiliate, or of the Company or an Affiliate to continue your employment. In addition, nothing in your option will obligate the Company or an Affiliate, their respective stockholders, boards of directors, officers or employees


  
 7 













 
to continue any relationship that you might have as a Director or Consultant for the Company or an Affiliate. 

15.        WITHHOLDING OBLIGATIONS. 

   (a)        At the time you exercise your option, in whole or
in part, and at any time thereafter as requested by the Company, you hereby authorize withholding from payroll and any other amounts payable to you, and otherwise agree to make adequate provision for (including by means of a “same day
sale” pursuant to a program developed under Regulation T as promulgated by the Federal Reserve Board to the extent permitted by the Company), any sums required to satisfy the federal, state, local and foreign tax withholding obligations of the
Company or an Affiliate, if any, which arise in connection with the exercise of your option. 

   (b)        If this option is a Nonstatutory Stock Option,
then upon your request and subject to approval by the Company, and compliance with any applicable legal conditions or restrictions, the Company may withhold from fully vested shares of Common Stock otherwise issuable to you upon the exercise of your
option a number of whole shares of Common Stock having a Fair Market Value, determined by the Company as of the date of exercise, not in excess of the minimum amount of tax required to be withheld by law (or such lower amount as may be necessary to
avoid classification of your option as a liability for financial accounting purposes). If the date of determination of any tax withholding obligation is deferred to a date later than the date of exercise of your option, share withholding pursuant to
the preceding sentence shall not be permitted unless you make a proper and timely election under Section 83(b) of the Code, covering the aggregate number of shares of Common Stock acquired upon such exercise with respect to which such
determination is otherwise deferred, to accelerate the determination of such tax withholding obligation to the date of exercise of your option. Notwithstanding the filing of such election, shares of Common Stock shall be withheld solely from fully
vested shares of Common Stock determined as of the date of exercise of your option that are otherwise issuable to you upon such exercise. Any adverse consequences to you arising in connection with such share withholding procedure shall be your sole
responsibility. 
    (c)        You may not exercise your
option unless the tax withholding obligations of the Company and/or any Affiliate are satisfied. Accordingly, you may not be able to exercise your option when desired even though your option is vested, and the Company will have no obligation to
issue a certificate for such shares of Common Stock or release such shares of Common Stock from any escrow provided for herein, if applicable, unless such obligations are satisfied. 

16.        TAX
CONSEQUENCES. You hereby agree that the Company does not have a duty to design or administer the Plan or its other compensation programs in a manner that minimizes your tax liabilities. You will not make any claim
against the Company, or any of its Officers, Directors, Employees or Affiliates related to tax liabilities arising from your option or your other compensation. In particular, you acknowledge that this option is exempt from Section 409A of the
Code only if the exercise price per share specified in the Grant Notice is at least equal to the “fair market value” per share of the Common Stock on the Date of Grant and there is no other impermissible deferral of compensation associated
with the option. Because the Common Stock is not traded on an established securities market, the Fair Market Value is determined by the Board, perhaps in consultation with an independent valuation firm retained by the Company. You


  
 8 













 
acknowledge that there is no guarantee that the Internal Revenue Service will agree with the valuation as determined by the Board, and you will not make any claim against the Company, or any of
its Officers, Directors, Employees or Affiliates in the event that the Internal Revenue Service asserts that the valuation determined by the Board is less than the “fair market value” as subsequently determined by the Internal Revenue
Service. 
 17.        NOTICES. Any notices provided
for in your option or the Plan will be given in writing (including electronically) and will be deemed effectively given upon receipt or, in the case of notices delivered by mail by the Company to you, five (5) days after deposit in the United
States mail, postage prepaid, addressed to you at the last address you provided to the Company. The Company may, in its sole discretion, decide to deliver any documents related to participation in the Plan and this option by electronic means or to
request your consent to participate in the Plan by electronic means. By accepting this option, you consent to receive such documents by electronic delivery and to participate in the Plan through an on-line or
electronic system established and maintained by the Company or another third party designated by the Company. 

18.        GOVERNING PLAN
DOCUMENT. Your option is subject to all the provisions of the Plan, the provisions of which are hereby made a part of your option, and is further subject to all interpretations, amendments, rules and regulations, which may from
time to time be promulgated and adopted pursuant to the Plan. If there is any conflict between the provisions of your option and those of the Plan, the provisions of the Plan will control. 

  
 9 













 ATTACHMENT II 

2014 EQUITY INCENTIVE PLAN 












 ATTACHMENT III 

NOTICE OF EXERCISE 












 NOTICE OF EXERCISE 

 

					
	 SYNTHORX, INC.
	  		  	
	 11099 N. TORREY PINES ROAD, SUITE 290
	  		  	
	 LA JOLLA, CA 92037
	  		  	Date of Exercise: _______________

 This constitutes notice to SYNTHORX, INC. (the
“Company”) under my stock option referenced below (the “Option”) that I elect to purchase the number of shares of Common Stock of the Company indicated below (the “Shares”)
for the price set forth below. 
  

					
	 Type of option (check one):
	  	 Incentive ☐
	  	 Nonstatutory ☐

			
	 Option dated:
	  	 ______________
	  	 ______________

			
	 Number of Shares as

to which Option is

exercised:
	  	 ______________
	  	 ______________

			
	 Certificates to be

issued in name of:
	  	 ______________
	  	 ______________

			
	 Total exercise price:
	  	 $_____________
	  	 $_____________

			
	 Cash payment delivered

herewith:
	  	 $_____________
	  	 $_____________


 By this exercise, I agree (i) to provide such additional documents as the Company may
require pursuant to the terms of the SYNTHORX, INC. 2014 EQUITY INCENTIVE PLAN, (ii) to provide for the payment by me to the Company (in the manner
designated by the Company) of the Company’s withholding obligation, if any, relating to the exercise of the Option, (iii) if this exercise relates to an incentive stock option, to notify the Company in writing within fifteen (15) days
after the date of any disposition of any of the Shares issued upon exercise of the Option that occurs within two (2) years after the date of grant of the Option or within one (1) year after such Shares are issued upon exercise of the
Option; and (iv) if, immediately after the issuance of shares of Common Stock to me pursuant to this Notice of Exercise, I will own one percent (1%) or more of the then outstanding capital stock of the Company (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), I will execute and deliver to the Company an Adoption Agreement or a counterpart signature page
(in the form(s) provided to me by the Company) to that certain Amended and Restated Right of First Refusal and Co-Sale Agreement, dated as of April 12, 2018 (as the same may be amended from time to time,
the “Co-Sale Agreement”), and that certain Amended and Restated Voting Agreement, dated as of April 12, 2018 (as the same may be amended from time to time, the “Voting
Agreement” and together with the Co-Sale Agreement, the “Stockholder Agreements”) and shall become a Stockholder (as defined in each of the Stockholder Agreements)
thereunder, and shall further deliver a Consent of Spouse (as defined in the Stockholder Agreements) if applicable. 












 I hereby make the following certifications and representations with respect
to the number of Shares listed above, which are being acquired by me for my own account upon exercise of the Option as set forth above: 

I acknowledge that the Shares have not been registered under the Securities Act of 1933, as amended (the
“Securities Act”), and are deemed to constitute “restricted securities” under Rule 701 and Rule 144 promulgated under the Securities Act. I warrant and represent to the Company that I have no present intention of
distributing or selling said Shares, except as permitted under the Securities Act and any applicable state securities laws. 

I further acknowledge that I will not be able to resell the Shares for at least ninety (90) days after the common stock
of the Company becomes publicly traded (i.e., subject to the reporting requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934) under Rule 701 and that more restrictive conditions apply to affiliates of the Company
under Rule 144, and that restrictions on resale may be imposed by the applicable securities laws of my jurisdiction of residence. 

I further acknowledge that all certificates representing any of the Shares subject to the provisions of the Option shall have
endorsed thereon appropriate legends reflecting the foregoing limitations, as well as any legends reflecting restrictions pursuant to the Company’s Certificate of Incorporation, Bylaws and/or applicable securities laws. 

I further agree that, if required by the Company (or a representative of the underwriters) in connection with the first
underwritten registration of the offering of any securities of the Company under the Securities Act, I will not sell, dispose of, transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar
transaction with the same economic effect as a sale with respect to any shares of Common Stock or other securities of the Company for a period of one hundred eighty (180) days following the effective date of a registration statement of the
Company filed under the Securities Act (or such longer period as the underwriters or the Company shall request to facilitate compliance with FINRA Rule 2711 or NYSE Member Rule 472 or any successor or similar rule or regulation) (the “Lock-Up Period”); provided, however, I understand that the Company may exercise its repurchase option, if any, during the Lock-Up Period. I further agree to
execute and deliver such other agreements as may be reasonably requested by the Company or the underwriters that are consistent with the foregoing or that are necessary to give further effect thereto. In order to enforce the foregoing covenant, the
Company may impose stop-transfer instructions with respect to securities subject to the foregoing restrictions until the end of such period. 

 

	
	 Very truly yours,

	
	  

	 (Sign name)

	
	  

	 (Print name)

	
	 Address:

	  

	
	  















 SYNTHORX, INC. 

EARLY EXERCISE STOCK PURCHASE AGREEMENT 

UNDER THE 2014 EQUITY INCENTIVE PLAN 

THIS EARLY EXERCISE STOCK PURCHASE
AGREEMENT (this “Agreement”) is made by and between Synthorx, Inc., a Delaware corporation (the “Company”), and [______] (“Purchaser”). 

WITNESSETH: 

WHEREAS, Purchaser holds a stock option dated [__________] to purchase shares of common
stock (“Common Stock”) of the Company (the “Option”) pursuant to the Company’s 2014 Equity Incentive Plan (the “Plan”); and 

WHEREAS, the Option consists of a Stock Option Grant Notice and an Option Agreement; and

 WHEREAS, Purchaser desires to exercise the Option on the terms and conditions
contained herein; and 
 WHEREAS, Purchaser wishes to take advantage of the early
exercise provision of Purchaser’s Option and therefore to enter into this Agreement; 
 NOW,
THEREFORE, IT IS AGREED between the Company and the Purchaser as follows: 

1.         INCORPORATION OF
PLAN AND OPTION BY REFERENCE. This Agreement is subject to all of the terms and conditions as set forth in the Plan and the Option. If there is a conflict between the
terms of this Agreement and/or the Option and the terms of the Plan, the terms of the Plan will control. If there is a conflict between the terms of this Agreement and the terms of the Option, the terms of the Option will control. Capitalized terms
not explicitly defined in this Agreement but defined in the Plan will have the same definitions as in the Plan. Capitalized terms not explicitly defined in this Agreement or the Plan but defined in the Option will have the same definitions as in the
Option. 
 2.        PURCHASE AND
SALE OF COMMON STOCK. 

(a)        Agreement to Purchase and Sell Common Stock. Purchaser
hereby agrees to purchase from the Company, and the Company hereby agrees to sell to Purchaser, shares of the Common Stock of the Company in accordance with the Notice of Exercise duly executed by Purchaser and attached hereto as
EXHIBIT A. 
 (b)        Closing. The closing
hereunder, including payment for and delivery of the Common Stock, will occur at the offices of the Company immediately following the execution of this Agreement, or at such other time and place as the parties may mutually agree; provided,
however, that if stockholder approval of the Plan is required before the Option may be exercised, 

  
 1. 













 
then the Option may not be exercised, and the closing will be delayed, until such stockholder approval is obtained. If such stockholder approval is not obtained within the time limit specified in
the Plan, then this Agreement will be null and void. 

(c)        Vesting. Notwithstanding the closing, the shares of
Common Stock that Purchaser acquires pursuant to your Option hereunder will continue to vest pursuant to the Vesting Schedule in the Option and will be subject to the Repurchase Option (as defined below) to the extent unvested, as further described
in Section 3 below. For purposes of this Agreement, “Vested Shares” will mean shares subject to the Option that have vested in accordance with the Vesting Schedule in the Option, and “Unvested
Shares” will mean shares subject to the Option that have not vested in accordance with the Vesting Schedule. 

3.        UNVESTED SHARE REPURCHASE
OPTION. 
 (a)        Repurchase Option. In the event
Purchaser’s Continuous Service terminates, then the Company will have an irrevocable option (the “Repurchase Option”) for a period of six (6) months after said termination (or in the case of shares issued upon
exercise of the Option after such date of termination, within six (6) months after the date of the exercise), or such longer period as may be agreed to by the Company and Purchaser (as applicable, the “Repurchase
Period”), to repurchase from Purchaser or Purchaser’s personal representative, as the case may be, those shares that Purchaser received pursuant to the exercise of the Option that are Unvested Shares as of such termination date.

 (b)        Share Repurchase Price. If the Company’s
Repurchase Option is triggered, the Company may repurchase all or any of the Unvested Shares at any time during the Repurchase Period at a price equal to the lower of (i) the Fair Market Value of the such shares (as determined under the Plan)
on the date of repurchase, or (ii) the price equal to Purchaser’s Exercise Price for such shares as indicated on Purchaser’s Stock Option Grant Notice. 

4.        EXERCISE OF
REPURCHASE OPTION. The Repurchase Option will be exercised by written notice signed by such person as designated by the Company, and delivered or mailed as provided herein. Such notice
will identify the number of Unvested Shares to be purchased and will notify Purchaser of the time, place and date for settlement of such purchase, which will be scheduled by the Company within the term of the Repurchase Option set forth above and
which settlement date shall be a date that is on or before the 30th day following the date of such notice. In addition, the Company shall be deemed to have exercised the Repurchase Option as of
the last day of the Repurchase Period, unless an officer of the Company notifies the holder of the Unvested Shares during the Repurchase Period in writing (delivered or mailed as provided herein) that the Company expressly declines to exercise its
Repurchase Option for some or all of the Unvested Shares, and provided that such deemed exercise will be deemed revoked by the Company on the 31st day following the last day of the Repurchase
Period if the Company has not paid for the repurchase of the Unvested Shares prior to such 31st day. The Company will be entitled to pay for any Unvested Shares purchased pursuant to its
Repurchase Option at the Company’s option in cash or by offset against any indebtedness owing to the Company by Purchaser, or by a combination of both. Upon delivery of such notice and payment of the purchase price in any of the ways described
above, the Company will become the legal and beneficial owner of the Unvested Shares being repurchased and all rights and interest therein or 

  
 2. 













 
related thereto, and the Company will have the right to transfer to its own name the Unvested Shares being repurchased by the Company, without further action by Purchaser. 

5.        CAPITALIZATION ADJUSTMENTS.
In the event of a Capitalization Adjustment, then any and all new, substituted or additional securities or other property to which Purchaser is entitled by reason of Purchaser’s ownership of Unvested Shares at such time will be immediately
subject to the Repurchase Option and be included in the word “Unvested Shares” for all purposes of the Repurchase Option with the same force and effect as the Unvested Shares subject to the Repurchase Option immediately before such
Capitalization Adjustment, but only to the extent there are Unvested Shares at the time covered by such Repurchase Option. While the aggregate price payable upon exercise of the Repurchase Option will remain the same after each such event, the price
payable per share upon exercise of the Repurchase Option will be appropriately adjusted. 

6.        CORPORATE TRANSACTIONS. To the
extent the Repurchase Option remains in effect following a Corporate Transaction or Change in Control, unless otherwise provided by the Board pursuant to the terms of the Plan, it will apply to the new capital stock or other property received in
exchange for the Unvested Shares in consummation of the Corporate Transaction or Change in Control, as applicable, but only to the extent the Unvested Shares were at the time covered by such right. Appropriate adjustments will be made to the price
per share payable upon exercise of the Repurchase Option to reflect the Corporate Transaction or Change in Control, as applicable, upon the Company’s capital structure; provided, however, that the aggregate price payable upon exercise of
the Repurchase Option will remain the same. 

7.        ESCROW OF UNVESTED
SHARES. As security for Purchaser’s faithful performance of the terms of this Agreement and to insure the availability for delivery of the Unvested Shares upon exercise of the Repurchase Option
herein provided for, Purchaser agrees that all Unvested Shares issued to Purchaser pursuant to the Option will be held in escrow pursuant to the terms of the Joint Escrow Instructions in substantially the form attached hereto as
EXHIBIT C. Purchaser agrees to execute and deliver, at the closing hereunder, to the individual designated as the escrow agent in the Joint Escrow Instructions or such person’s designee (the “Escrow
Agent”), (i) the Joint Escrow Instructions and (ii) three (3) Stock Assignment Separate from Certificates duly endorsed (with date and number of shares blank) substantially in the form attached hereto as EXHIBIT
B and deliver the same, along with the certificate or certificates evidencing all of the Unvested Shares, if applicable, which will be held and used by the Escrow Agent pursuant to the terms of the Joint Escrow Instructions. 

8.        RIGHTS OF
PURCHASER. Subject to the provisions of the Option, Purchaser will exercise all rights and privileges of a stockholder of the Company with respect to the Unvested Shares deposited in escrow. Purchaser
will be deemed to be the holder of the Unvested Shares for purposes of receiving any dividends that may be paid with respect to such shares (which will be subject to the same vesting and forfeiture restrictions as apply to the shares to which they
relate) and for purposes of exercising any voting rights relating to such shares, even if some or all of such shares have not yet vested and been released from the Company’s Repurchase Option. 

9.        TRANSFER
RESTRICTIONS. In addition to any other limitation on transfer created by this Agreement or applicable securities laws, Purchaser will not sell, assign, hypothecate,


  
 3. 













 
donate, encumber or otherwise dispose of any interest in the Unvested Shares while such shares are subject to the Repurchase Option; provided, however, that an interest in such shares may
be transferred pursuant to a qualified domestic relations order as defined in the Code or Title I of the Employee Retirement Income Security Act of 1974. In the case of Vested Shares released from the Repurchase Option, Purchaser may not sell,
assign, hypothecate, donate, encumber or otherwise dispose of all or any part of such Vested Shares or any interest therein except in compliance with this Agreement, the Option Agreement, Company’s bylaws and applicable securities laws. 

10.        RESTRICTIVE LEGENDS. 

  (a)        The certificate(s) representing the Common Stock issued
to you pursuant to the Option will be endorsed with appropriate legends or will bear notations as determined by the Company in substantially the following forms (in addition to any other legend or notations that may be required by other agreements
between you and the Company): 
 (i)        “THE SHARES REPRESENTED
HEREBY ARE SUBJECT TO A REPURCHASE OPTION AND OTHER RESTRICTIONS AND CONDITIONS SET FORTH IN AN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER, OR SUCH HOLDER’S PREDECESSOR IN INTEREST, A COPY OF WHICH IS ON FILE AT THE PRINCIPAL
OFFICE OF THIS COMPANY. ANY TRANSFER OR ATTEMPTED TRANSFER OF ANY SHARES SUBJECT TO SUCH OPTION IS VOID WITHOUT THE PRIOR EXPRESS WRITTEN CONSENT OF THE COMPANY.” 

(ii)        “THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933 AS AMENDED. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT AS TO THE SECURITIES UNDER SAID ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT
SUCH REGISTRATION IS NOT REQUIRED.” 
 (iii)        “THE SHARES
REPRESENTED HEREBY ARE SUBJECT TO A RIGHT OF FIRST REFUSAL OPTION IN FAVOR OF THE COMPANY AND/OR ITS ASSIGNEE(S) AND ACCORDINGLY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF EXCEPT IN CONFORMITY WITH THE TERMS OF
THE BYLAWS OF THE COMPANY AND/OR AN OPTION AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER, OR SUCH HOLDER’S PREDECESSOR IN INTEREST, A COPY OF WHICH IS ON FILE AT THE COMPANY’S PRINCIPAL CORPORATE OFFICES.” 

(iv)        Any legend required by applicable blue sky laws. 

  (b)        Upon the lapse of any restrictions relating to the
Common Stock issued to you pursuant to the Option, the Company shall deliver to you or your personal representative a stock certificate representing a number of shares of Common Stock, free of the restrictive legend described above, equal to the
number of shares of Common Stock with respect to which such restrictions have lapsed. If certificates representing such shares of Common Stock shall have 

  
 4. 













 
theretofore been delivered to you, such certificates shall be returned to the Company, complete with any necessary signatures or instruments of transfer prior to the issuance by the Company of
such unlegended shares of Common Stock. 

11.        INVESTMENT REPRESENTATIONS. In
connection with the purchase of the Common Stock under the Option, Purchaser represents to the Company the following: 

   (a)        Purchaser is aware of the Company’s business
affairs and financial condition and has acquired sufficient information about the Company to reach an informed and knowledgeable decision to acquire the Common Stock. Purchaser is acquiring the Common Stock for investment for Purchaser’s own
account only and not with a view to, or for resale in connection with, any “distribution” thereof within the meaning of the Securities Act. 

   (b)        Purchaser understands that the Common Stock has
not been registered under the Securities Act by reason of a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of Purchaser’s investment intent as expressed herein. 

   (c)        Purchaser further acknowledges and understands
that the Common Stock must be held indefinitely unless the Common Stock is subsequently registered under the Securities Act or an exemption from such registration is available. Purchaser further acknowledges and understands that the Company is under
no obligation to register the Common Stock. Purchaser understands that the certificate evidencing the Common Stock will be imprinted with a legend that prohibits the transfer of the Common Stock unless the Common Stock is registered or such
registration is not required in the opinion of counsel for the Company. 

   (d)        Purchaser is familiar with the provisions of
Rules 144 and 701, under the Securities Act, as in effect from time to time, which, in substance, permit limited public resale of “restricted securities” acquired, directly or indirectly, from the issuer thereof (or from an affiliate
of such issuer), in a non-public offering subject to the satisfaction of certain conditions. Rule 701 provides that if the issuer qualifies under Rule 701 at the time of issuance of the securities, such
issuance will be exempt from registration under the Securities Act. In the event the Company becomes subject to the reporting requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the securities exempt under Rule 701
may be sold by Purchaser ninety (90) days thereafter, subject to the satisfaction of certain of the conditions specified by Rule 144 and the market stand-off provision described in Purchaser’s
Option Agreement. 
    (e)        In the event that the sale
of the Common Stock does not qualify under Rule 701 at the time of purchase, then the Common Stock may be resold by Purchaser in certain limited circumstances subject to the provisions of Rule 144, which requires, among other things:
(i) the availability of certain public information about the Company, and (ii) the resale occurring following the required holding period under Rule 144 after Purchaser has purchased, and made full payment of (within the meaning of Rule
144), the securities to be sold. 
    (f)        Purchaser
further understands that at the time Purchaser wishes to sell the Common Stock there may be no public market upon which to make such a sale, and that, even if such a public market then exists, the Company may not be satisfying the current public
current 

  
 5. 













 
information requirements of Rule 144 or 701, and that, in such event, Purchaser would be precluded from selling the Common Stock under Rule 144 or 701 even if the minimum holding period
requirement had been satisfied. 
   (g)        Purchaser further
warrants and represents that Purchaser has either (i) preexisting personal or business relationships, with the Company or any of its officers, directors or controlling persons, or (ii) the capacity to protect his own interests in
connection with the purchase of the Common Stock by virtue of the business or financial expertise of Purchaser or of professional advisors to Purchaser who are unaffiliated with and who are not compensated by the Company or any of its affiliates,
directly or indirectly. Purchaser further warrants and represents that Purchaser’s purchase the Common Stock was not accomplished by the publication of any advertisement. 

12.        TAX CONSEQUENCES. Purchaser
agrees to review with Purchaser’s own tax advisors the federal, state, local and foreign tax consequences of this investment and the transactions contemplated by this Agreement. Purchaser will rely solely on such advisors and not on any
statements or representations of the Company or any of its agents. Purchaser understands that Purchaser (and not the Company) will be responsible for Purchaser’s tax liability that may arise as a result of this investment or the transactions
contemplated by this Agreement. Purchaser understands that Section 83(a) of the Code generally taxes as ordinary income to Purchaser the difference between the amount paid for the Common Stock and the fair market value of such Common
Stock as of the date any restrictions on the Common Stock lapse (that is, as of the date on which part of all of such shares vest). In this context, “restriction” includes the right of the Company to buy back the Common Stock pursuant to
the Repurchase Option set forth above. Purchaser understands that Purchaser may elect to be taxed at the time the Common Stock is purchased, rather than when and as the Repurchase Option expires, by filing an election under Section 83(b) of the
Code (an “83(b) Election”) with the Internal Revenue Service within thirty (30) days of the date of purchase, a form of which is included as EXHIBIT D. Even if the fair market value of the Common
Stock at the time of the execution of this Agreement equals the amount paid for the Common Stock, the 83(b) Election must be made to potentially avoid income under Section 83(a) in the future. Purchaser understands that failure to file such an 83(b)
Election in a timely manner may result in adverse tax consequences for Purchaser. Purchaser further understands that Purchaser must file an additional copy of such 83(b) Election with Purchaser’s federal income tax return for the calendar year
in which the date of this Agreement falls. Purchaser acknowledges that the foregoing is only a summary of the effect of U.S. federal income taxation with respect to purchase of the Common Stock hereunder, and does not purport to be complete.
Purchaser further acknowledges that the Company has directed Purchaser to seek independent advice regarding the applicable provisions of the Code, the income tax laws of any municipality, state or foreign country in which Purchaser may reside, and
the tax consequences of Purchaser’s death. Purchaser assumes all responsibility for filing an 83(b) Election and paying all taxes resulting from such election or the lapse of the restrictions on the Common Stock. PURCHASER ACKNOWLEDGES
THAT IT IS PURCHASER’S OWN RESPONSIBILITY, AND NOT THE COMPANY’S, TO FILE A TIMELY ELECTION UNDER SECTION 83(B) OF THE CODE. THE COMPANY AND ITS LEGAL COUNSEL CANNOT ASSUME RESPONSIBILITY FOR FAILURE TO FILE THE 83(B)
ELECTION IN A TIMELY MANNER UNDER ANY CIRCUMSTANCES. 

  
 6. 














13.        REFUSAL TO
TRANSFER. The Company will not be required (a) to transfer on its books any shares of Common Stock of the Company that has been transferred in violation of any of the provisions set forth in this
Agreement, or (b) to treat as owner of such shares or to accord the right to vote as such owner or to pay dividends to any transferee to whom such shares have been so transferred. 

14.        NOTICES. All
notices required or permitted hereunder, in your Option or the Plan will be given in writing (including electronically) and will be deemed effectively given upon receipt or, in the case of notices delivered by the Company to Purchaser, five days
after deposit in the U.S. mail, postage prepaid, addressed to Purchaser at the last address Purchaser provided to the Company. The Company may, in its sole discretion, decide to deliver any documents related to participation in the Plan, the
Option and this Agreement by electronic means or to request Purchaser consent to participate in the Plan by electronic means. By entering into this Agreement, Purchaser consents to receive such documents by electronic delivery and to participate in
the Plan through an on-line or electronic system established and maintained by the Company or another third party designated by the Company. 

15.        GOVERNING OPTION
DOCUMENT. The Common Stock purchased hereunder is subject to all the provisions of the Option (including the Stock Option Grant Notice, Option Agreement and governing Plan) to which such shares relate,
the provisions of which are hereby made a part of this Agreement, and is further subject to all interpretations, amendments, rules and regulations which may from time to time be promulgated and adopted pursuant to the Plan. In the event of any
conflict between the provisions of this Agreement and those of the Option, the provisions of the Option will control. 

16.        NO EMPLOYMENT OR
SERVICE RIGHTS. This Agreement is not an employment or service contract and nothing in this Agreement shall affect in any manner whatsoever the right or power of the Company or its
affiliates to terminate Purchaser’s employment or service relationship for any reason at any time, with or without cause and with or without notice. 

17.        MISCELLANEOUS. 

   (a)        Successors and Assigns. This Agreement will inure
to the benefit of the successors and assigns of the Company and, subject to the restrictions on transfer herein set forth, be binding upon Purchaser, Purchaser’s successors, and assigns. The Company may assign the Repurchase Option hereunder at
any time or from time to time, in whole or in part. 

   (b)        Attorneys’ Fees; Specific Performance.
Purchaser will reimburse the Company for all costs incurred by the Company in enforcing the performance of, or protecting its rights under, any part of this Agreement, including reasonable costs of investigation and attorneys’ fees. It is
the intention of the parties that the Company, upon exercise of the Repurchase Option and payment for the shares repurchased, pursuant to the terms of this Agreement, will be entitled to receive the Common Stock, in specie, in order to have
such Common Stock available for future issuance without dilution of the holdings of other stockholders. Furthermore, it is expressly agreed between the parties that money damages are inadequate to compensate the Company for the Common Stock and that
the Company will, upon 

  
 7. 













 
proper exercise of the Repurchase Option, be entitled to specific enforcement of its rights to purchase and receive said Common Stock. 

   (c)        Governing Law; Venue. This Agreement will be
governed by and construed in accordance with the laws of the State of California. The parties agree that any action brought by either party to interpret or enforce any provision of this Agreement will be brought in, and each party agrees to, and
does hereby, submit to the jurisdiction and venue of, the appropriate state or federal court for the district encompassing the Company’s principal place of business. 

   (d)        Further Execution. The parties agree to take all
such further action(s) as may reasonably be necessary to carry out and consummate this Agreement as soon as practicable, and to take whatever steps may be necessary to obtain any governmental approval in connection with or otherwise qualify the
issuance of the securities that are the subject of this Agreement. 

   (e)        Independent Counsel. Purchaser acknowledges that
this Agreement has been prepared on behalf of the Company by Cooley LLP, counsel to the Company and that Cooley LLP does not represent, and is not acting on behalf of, Purchaser. Purchaser has been provided with an opportunity to consult with
Purchaser’s own counsel with respect to this Agreement. 

   (f)        Entire Agreement; Amendment. This Agreement
constitutes the entire agreement between the parties with respect to the subject matter hereof and supersedes and merges all prior agreements or understandings, whether written or oral. This Agreement may not be amended, modified or revoked, in
whole or in part, except by an agreement in writing signed by each of the parties hereto. 

   (g)        Severability. If one or more provisions of this
Agreement are held to be unenforceable under applicable law, the parties agree to renegotiate such provision in good faith. In the event that the parties cannot reach a mutually agreeable and enforceable replacement for such provision, then
(i) such provision will be excluded from this Agreement, (ii) the balance of the Agreement will be interpreted as if such provision were so excluded and (iii) the balance of the Agreement will be enforceable in accordance with its
terms. 
    (h)        Counterparts. This Agreement may be
executed in counterparts, each of which will be deemed an original and all of which together will constitute one 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. 

  
 8. 













 IN WITNESS WHEREOF, the
parties hereto have executed this Early Exercise Stock Purchase Agreement as of ___________, ____. 
  

	
	SYNTHORX, INC.
	
	 By________________________________________

	 Name:_____________________________________

	 Title:_____________________________________

	 Address:__________________________________

	
              __________________________________

	
	PURCHASER
	
	 Signed:_____________________________________

	 Print Name:_________________________________

	 Address:____________________________________

	
              ____________________________________




  
 9. 













 ATTACHMENTS: 

 

			
	 EXHIBIT A
	  	 NOTICE OF EXERCISE

	EXHIBIT B	  	 STOCK ASSIGNMENT SEPARATE FROM
CERTIFICATE

	EXHIBIT C	  	 JOINT ESCROW INSTRUCTIONS

	EXHIBIT D	  	 FORM OF 83(B) ELECTION














 EXHIBIT A 

NOTICE OF EXERCISE 












 EXHIBIT B 

STOCK ASSIGNMENT SEPARATE FROM CERTIFICATE 

FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers
unto SYNTHORX, INC., a Delaware corporation (the “Company”), pursuant to the Repurchase Option under that certain Early Exercise Stock Purchase Agreement, dated __________, 20___ by
and between the undersigned and the Company (the “Agreement”), ________ shares of Common Stock of the Company standing in the undersigned’s name on the books of the Company represented by Certificate No(s). ___________
and does hereby irrevocably constitute and appoint both the Company’s Secretary and the Company’s attorney, or either of them, to transfer said shares of Common Stock on the books of the Company with full power of substitution in the
premises. This Assignment may be used only in accordance with and subject to the terms and conditions of the Agreement, in connection with the repurchase of shares of Common Stock of the Company issued to the undersigned pursuant to the Agreement,
and only to the extent that such shares remain subject to the Company’s Repurchase Option under the Agreement. 
 Dated:
_______________ 
  

	
	  

	 (Signature)

	
	  

	 (Print Name)



 (INSTRUCTION: Please do not fill in any blanks other than the
“Signature” line and the “Print Name” line. The purpose of this Assignment is to enable the Company to exercise its Repurchase Option set forth in the Agreement without requiring additional signatures on your part.) 












 EXHIBIT C 

JOINT ESCROW INSTRUCTIONS 

Secretary 
 Synthorx, Inc. 

11099 N. Torrey Pines Road, Suite 290 
 La Jolla, CA 92037 

Dear Sir or Madam: 

As Escrow Agent for both Synthorx, Inc., a Delaware corporation (the “Company”), and the undersigned
purchaser (the “Purchaser”) of Common Stock of the Company (the “Common Stock”), you are hereby authorized and directed to hold the documents delivered to you pursuant to the terms of that certain
Early Exercise Stock Purchase Agreement (the “Agreement”), dated __________ to which a copy of these Joint Escrow Instructions is attached as EXHIBIT C, in
accordance with the following instructions: 
 1.        In the event the
Company or an affiliate or assignee of the Company will elect to exercise the Repurchase Option set forth in the Agreement, the Company or its affiliate or assignee, as applicable, will give to Purchaser and you a written notice specifying the
number of shares of Common Stock to be purchased, the purchase price, and the time for a closing hereunder at the principal office of the Company. Purchaser and the Company hereby irrevocably authorize and direct you to close the transaction
contemplated by such notice in accordance with the terms of said notice. 

2.        At the closing you are directed (a) to date any stock
assignments necessary for the transfer of the certificate(s) evidencing the shares in question, (b) to fill in the number of shares of Common Stock being transferred, and (c) to deliver the same, together with the certificate(s) evidencing
the shares of Common Stock to be transferred to the Company against the simultaneous delivery to you of the purchase price (which may include suitable acknowledgment of cancellation of indebtedness) of the number of shares of Common Stock being
purchased pursuant to the exercise of the Repurchase Option. 

3.        Purchaser irrevocably authorizes the Company to deposit with you the
certificate(s) evidencing shares of Common Stock to be held by you hereunder and any additions and substitutions to said shares of Common Stock as specified in the Agreement. Purchaser does hereby irrevocably constitute and appoint you as the
Purchaser’s attorney-in-fact and agent for the term of this escrow to execute with respect to such securities and other property all documents of assignment and/or
transfer and all stock certificates necessary or appropriate to make all securities negotiable and complete any transaction herein contemplated. 

4.        This escrow will terminate and the shares of Common Stock held
hereunder will be released in full upon the earlier of the expiration or exercise in full of the Repurchase Option. 












 5.        If at the time of
termination of this escrow you should have in your possession any documents, securities, or other property belonging to Purchaser, you will deliver all of same to Purchaser and will be discharged of all further obligations hereunder; provided,
however, that if at the time of termination of this escrow you are advised by the Company that the property subject to this escrow is the subject of a pledge or other security agreement, you will deliver all such property to the pledgeholder or
other person designated by the Company. 
 6.        Except as otherwise
provided in these Joint Escrow Instructions, your duties hereunder may be altered, amended, modified or revoked only by a writing signed by all of the parties hereto. 

7.        You will be obligated only for the performance of such duties as are
specifically set forth herein and may rely and will be protected in relying or refraining from acting on any instrument reasonably believed by you to be genuine and to have been signed or presented by the proper party or parties or their assignees.
You will not be personally liable for any act you may do or omit to do hereunder as Escrow Agent or as attorney-in-fact for Purchaser while acting in good faith and any
act done or omitted by you pursuant to the advice of your own attorneys will be conclusive evidence of such good faith. 

8.        You are hereby expressly authorized to disregard any and all warnings
given by any of the parties hereto or by any other person or entity, excepting only orders or process of courts of law, and are hereby expressly authorized to comply with and obey orders, judgments or decrees of any court. In case you obey or comply
with any such order, judgment or decree of any court, you will not be liable to any of the parties hereto or to any other person, firm or corporation by reason of such compliance, notwithstanding any such order, judgment or decree being subsequently
reversed, modified, annulled, set aside, vacated or found to have been entered without jurisdiction. 

9.        You will not be liable in any respect on account of the identity,
authority or rights of the parties executing or delivering or purporting to execute or deliver the Agreement or any documents or papers deposited or called for hereunder. 

10.        You will not be liable for the outlawing of any rights under any
statute of limitations with respect to these Joint Escrow Instructions or any documents deposited with you. 

11.        Your responsibilities as Escrow Agent hereunder will terminate if
you cease to be Secretary of the Company or if you resign by written notice to the Company. In the event of any such termination, the Secretary of the Company will automatically become the successor Escrow Agent unless the Company appoints another
successor Escrow Agent, and Purchaser hereby confirms the appointment of such successor as Purchaser’s attorney-in-fact and agent to the full extent of your
appointment. 
 12.        If you reasonably require other or further
instruments in connection with these Joint Escrow Instructions or obligations in respect hereto, the necessary parties hereto will join in furnishing such instruments. 

  
 2. 













 13.        It is understood
and agreed that should any dispute arise with respect to the delivery and/or ownership or right of possession of the securities, you are authorized and directed to retain in your possession without liability to anyone all or any part of said
securities until such dispute has been settled either by mutual written agreement of the parties concerned or by a final order, decree or judgment of a court of competent jurisdiction after the time for appeal has expired and no appeal has been
perfected, but you will be under no duty whatsoever to institute or defend any such proceedings. 

14.        All notices required or permitted hereunder shall be in writing and
shall be deemed effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed telex or facsimile if sent during normal business hours of the recipient, and if not during normal business hours of the
recipient, then on the next business day, (c) five (5) calendar 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, specifying next day delivery, with written verification of receipt. All communications shall be sent to the other party hereto at such party’s address set forth below, or at such other address as such party may designate by
ten (10) days advance written notice to the other party hereto: 
  

							
		 	 COMPANY:
	  	 Synthorx, Inc.
	  	
		 		  	 11099 N. Torrey Pines Road, Suite 290
	  	
		 		  	 La Jolla, CA 92037
	  	
				
		 	 PURCHASER:
	  	  
	  	
		 		  	  
	  	
		 		  	  
	  	
				
		 	 ESCROW AGENT:
	  	 Attn: Secretary of Synthorx, Inc.
	  	
		 		  	 11099 N. Torrey Pines Road, Suite 290
	  	
		 		  	 La Jolla, CA 92037
	  	

 15.        By signing these Joint Escrow
Instructions you become a party hereto only for the purpose of said Joint Escrow Instructions; you do not become a party to the Agreement. 

16.        You are entitled to employ such legal counsel, including without
limitation Cooley LLP, and other experts as you may deem necessary to advise you in connection with your obligations hereunder. You may rely upon the advice of such counsel, and may pay such counsel reasonable compensation therefor. The Company will
be responsible for all fees generated by such legal counsel in connection with your obligations hereunder. 

17.        This instrument will be binding upon and inure to the benefit of the
parties hereto and their respective successors and permitted assigns. It is understood and agreed that references to “you” or “your” herein refer to the original Escrow Agent and to any and all successor Escrow Agents. It is
understood and agreed that the Company may at any time or from time to time assign its rights under the Agreement and these Joint Escrow Instructions in whole or in part. 

  
 3. 













 18.        These Joint Escrow
Instructions will be governed by and interpreted and determined in accordance with the laws of the State of California, as such laws are applied by California courts to contracts made and to be performed entirely in California by residents of that
state. The parties hereby expressly consent to the personal jurisdiction of the state and federal courts located in the county in which the Company has its principal offices for any lawsuit arising from or related to this Agreement. 

  
 4. 













 
	
	 Very truly yours,

	
	SYNTHORX, INC.
	
	
By                      
                                         
 

	
	
Title                      
                                       


	
	PURCHASER:
	
	  

	 (Signature)

	
	  

	 (Print Name)



  

	
	ESCROW AGENT:
	
	  

	 (Signature)

	
	  

	 (Print Name)



  
 5. 













 INSTRUCTIONS FOR FILING
SECTION 83(b) ELECTION 
 Attached is a form of election under Section 83(b) of
the Internal Revenue Code and an accompanying IRS cover letter. Please fill in your social security number and sign the election and cover letter, then proceed as follows: 
  

	(a)	 Make three copies of the completed election form and one copy of the IRS cover letter.



  

	(b)	 Send the original signed election form and cover letter, the copy of the cover letter,
and a self-addressed stamped return envelope to the Internal Revenue Service Center where you would otherwise file your tax return1. Even if an address for an Internal Revenue Service Center is
already included in the forms below, it is your obligation to verify such address. This can be done by searching for the term “where to file” on www.irs.gov or by calling 1 (800) 829-1040.



 Sending the election via certified mail, requesting a return receipt, with the certified mail number
written on the cover letter is also recommended. 
  

	(c)	 Deliver one copy of the completed election form to the Company. 



 

	(d)	 Applicable state law may require that you attach a copy of the completed election form to your 2018 state
personal income tax return(s) when you file it for the year (assuming you file a state personal income tax return).2 



Please consult your personal tax advisor(s) to determine whether or not a copy of this Section 83(b) election should be
filed with your state personal income tax return(s). 
  

	(e)	 Retain one copy of the completed election form for your personal permanent records. 



Note: An additional copy of the completed election form must be delivered to the transferee (recipient) of the property if the
service provider and the transferee are not the same person. 
 Please note that the election must be filed with the IRS within 30 days of the date of
your restricted stock grant. Failure to file within that time will render the election void and you may recognize 
  

 
 1 Note: Per Treasury Regulation § 1.83-2(c), the Section 83(b) election must be filed with the IRS office where the person otherwise files his or her tax return. As of October 2016,
if you live in a foreign country or are a dual status alien (foreigners that will have lived both in their home country and the United States during the year in which they make the election) you should send the 83(b) election to Austin, TX
73301-0215. You can verify this is still the correct address at: http://www.irs.gov/uac/Where-to-File-Addresses-for--Taxpayers-and--Tax-Professionals-Filing-Form-1040. 

2 Note: Pursuant to Treasury Regulations finalized in July 2016 (Treas. Reg.
§ 1.83-2(c); T.D. 9779), taxpayers are no longer required to submit a copy of a Code Sec. 83(b) election with their federal personal income tax returns for the year in which the property subject to the election was transferred.
However, you are strongly encouraged to retain a copy of the completed election form and the IRS filed-stamped copy of your cover letter along with a copy of the federal personal income tax return for the year in which the property subject to the
election was transferred for your personal permanent records in case you ever need to demonstrate proper and timely filing (a common requirement imposed by acquirers in M&A transactions). 












 
ordinary taxable income as your vesting restrictions lapse. The Company and its counsel cannot assume responsibility for failure to file the election in a timely manner under any circumstances.


  
 2. 













 SECTION 83(b) ELECTION 

____________, 20___ 
 Department of the Treasury

 Internal Revenue Service 
 [City, State Zip]3[Austin, TX 73301-0215 
 USA]4 

Re:     Election Under Section 83(b) 

Ladies and Gentlemen: 
 The
undersigned taxpayer hereby elects, pursuant to Section 83(b) of the Internal Revenue Code of 1986, as amended, to include in gross income as compensation for services the excess (if any) of the fair market value of the shares described below
over the amount paid for those shares. The following information is supplied in accordance with Treasury Regulation § 1.83-2: 
  

	1.	 The name, social security number, address of the undersigned, and the taxable year for which this
election is being made are: 



							
		 	 Name:
	  	
                       
     
	  	
		 	 Social Security Number:
	  	
                       
     
	  	
		 	 Address:
	  	
                       
     
	  	
		 		  	
                       
     
	  	
		 	 Taxable year: Calendar year 20[.].
	  	

  

	2.	 The property that is the subject of this election: [______] shares of common stock of
SYNTHORX, INC., a Delaware corporation (the “Company”). 


  

	3.	 The property was transferred on: ______________, 20[.]. 



 

	4.	 The property is subject to the following restrictions: Some or all of the shares are subject to
forfeiture or repurchase at less than their fair market value if the undersigned does not continue to provide services for the Company for a designated period of time. The risk of forfeiture or repurchase lapses over a specified vesting period.



  
  

3 Note: Per Treasury Regulation § 1.83-2(c), the Section 83(b) election
must be filed with the IRS office where the person otherwise files his or her tax return. Assuming these are individual taxpayers who would file a Form 1040, see
http://www.irs.gov/uac/Where-to-File-Addresses-for--Taxpayers-and--Tax-Professionals-Filing-Form-1040. Use the address in the row which includes the state in which the service provider lives and in the column entitled “And you ARE
NOT enclosing a payment”. 
 4 Note: Per Treasury Regulation
§ 1.83-2(c), the Section 83(b) election must be filed with the IRS office where the person otherwise files his or her tax return. As of October 2016, if you live in a foreign country or are a dual status alien (foreigners that will have lived
both in their home country and the United States during the year in which they make the election) you should send the 83(b) election to Austin, TX 73301-0215. You can verify this is still the correct address at:
http://www.irs.gov/uac/Where-to-File-Addresses-for--Taxpayers-and--Tax-Professionals-Filing-Form-1040. 

  
 3. 














	5.	 The fair market value of the property at the time of transfer (determined without regard to any
restriction other than a nonlapse restriction as defined in Treasury Regulation § 1.83-3(h)): $[•] per share x [#] shares = $[•]. 



 

	6.	 For the property transferred, the undersigned paid: $[•] per share x [#] shares = $[•].



  

	7.	 The amount to include in gross income is:
$[•].5 


 The undersigned taxpayer will file this election with
the Internal Revenue Service office with which taxpayer files his or her annual income tax return not later than 30 days after the date of transfer of the property. A copy of the election also will be furnished to the person for whom the services
were performed and the transferee of the property. Additionally, the undersigned will include a copy of the election with his or her income tax return for the taxable year in which the property is transferred. The undersigned is the person
performing the services in connection with which the property was transferred. 
  

	
	 Very truly yours,

	
	  

	 [Name]



  
  

5 Note: This should equal the amount in Item 5 minus the amount in Item 6,
and in many cases will be $0.00. 

  
 4. 













 RETURN SERVICE REQUESTED 

Department of the Treasury 
 Internal Revenue Service 

[City, State, ZIP][Austin, TX 73301-0215 

USA] 
 Re:
      Election Under Section 83(b) of the Internal Revenue Code 
 Dear Sir
or Madam: 
 Enclosed please find an executed form of election under Section 83(b) of the Internal Revenue Code of
1986, as amended, filed with respect to an interest in Synthorx, Inc. 
 Also enclosed is a copy of the signed form of
election under Section 83(b). Please acknowledge receipt of these materials by marking the copy when received and returning it in the enclosed stamped, self-addressed envelope. 

Thank you very much for your assistance. 

 

	
	 Very truly yours,

	
	  

	 [Name]



 Enclosures 

  
 5.