September 25, 2019 John Evans Dear John:

Position and Duties.

Effective as of the Effective Date, you will continue to be employed by the Company, on a full-time basis, as its President and Chief Executive Officer and shall have all the duties, responsibilities and authority commensurate with these positions, subject to the supervision of, and reporting directly to, the Company’s Board of Directors (the “Board”).

For so long as you serve as Chief Executive Officer of the Company, at each annual meeting of the Company’s stockholders, the Company shall nominate you to serve as a member of the Board, and, if so elected at such meeting, you shall continue to serve as a member of the Board. Upon your cessation of service as Chief Executive Officer of the Company you shall be deemed to have voluntarily resigned from the Board, effective immediately.

You agree to perform the duties and responsibilities of your positions, and such other duties and responsibilities as shall from time to time be mutually agreed upon between you and the Board. You agree that, while employed by the Company, you will devote substantially all of your business time and your best efforts, business judgment, skill and knowledge exclusively to the advancement of the business and interests of the Company and to the discharge of your duties and responsibilities for it; provided, however, it is agreed that you may serve on up to two (2) outside boards (with prior notice to and approval by the Board, which approval shall not be unreasonably withheld), participate in charitable and civic organizations, and remain a Venture Partner of ARCH Venture Partners, in each case, to the extent such activities do not individually or in the aggregate interfere with your duties and responsibilities to the Company or create an actual or potential conflict of interests with the Company’s business. You agree to abide by the written rules, personnel practices and policies of the Company, as adopted and amended from time to time by the Company.

Salary. You will receive an annual base salary of $535,000, less applicable tax and other withholdings and deductions, payable in accordance with the normal payroll practices of the Company in effect from time to time. Your performance will be reviewed by the Compensation Committee of the Board (the “Compensation Committee”) on an annual basis in conjunction with an annual salary review.

Bonus Eligibility. You will be eligible to receive an annual cash incentive bonus with a target amount equal to 55% of your then-current annual base salary. Your annual bonus will be subject to the terms of the applicable bonus plan developed and approved by the Board or the Compensation Committee. Any bonus awarded will be paid, subject to required withholdings and deductions, on or before March 15 of the calendar year immediately following the year for which the bonus was awarded, subject to your employment at the end of the calendar year for which the bonus is due, except as otherwise expressly provided for herein.

Benefits. You will be eligible to participate in any and all benefit programs that the Company establishes and makes available to its employees from time to, time, provided that you are eligible under (and subject to all provisions of) the plan documents that govern those programs. Benefits are subject to change at any time in the Company’s sole discretion. In addition, the Company will reimburse you for all reasonable business expenses incurred by you in the performance of your duties, subject to the Company’s expense reimbursement policies applicable to senior executives in effect from time to time. You will be entitled to paid vacation time in accordance with the policies of the Company.

Termination of Employment; Change in Control.

This Agreement shall not be construed as an agreement, either express or implied, to employ you for any stated term, and shall in no way alter the Company’s policy of employment at-will, under which both the Company and you remain free to end the employment relationship for any reason, at any time, with or without cause or notice; provided, however, in the event you elect to terminate your employment without Good Reason, you agree to provide the Company with at least thirty (30) days’ advance written notice. Although your job duties, title, compensation and benefits, as well as the Company’s personnel policies and procedures, may change from time to time, the “at-will” nature of your employment may only be changed by a written agreement signed by you and a member of the Board, which expressly states the intention to modify the at-will nature of your employment.

In the event your employment with the Company terminates, on your last day of employment, you will receive your base salary and all accrued but unused vacation time through the last day of your employment, in accordance with the Company’s then-current payroll policies and practices (the “Termination Payment”). Without otherwise limiting the “at-will” nature of your employment, in the event your employment is terminated by the Company (or any successor or assign) without Cause or by you for Good Reason, then, subject to your remaining available to provide consulting services to the Company as reasonably requested by the Board upon reasonable notice and at mutually agreeable times, in addition to the Termination Payment, the Company shall provide the following payments and benefits (“Severance Benefits”): (i) continued payment of your base salary at the then-current rate per pay period, reduced by all applicable taxes and withholdings, for a period of twelve (12) months following your termination date, in accordance with the Company’s then-current payroll policies and practices; (ii) payment of your then-applicable target bonus amount, pro-rated for the portion of the then-current calendar year during which you were employed by the Company including any notice periods, within sixty (60) days following the last day of your employment; (iii) continued vesting for twelve (12) months of any unvested portion of any equity awards then held by you; (iv) to the extent then vested and outstanding, the stock option grants awarded to you by the Company on each of May 8, 2018 and July 13, 2018 shall remain outstanding and exercisable for the lesser of the remaining term or a twenty-four (24) month period following such termination; and (v) provided you timely elect and remain eligible for coverage pursuant to Part 6 of Title I of ERISA, or similar state law (collectively, “COBRA”), payment or reimbursement to you of an amount equal to the full monthly premium for COBRA continuation coverage under the Company’s medical plans as in effect on the date of your termination with respect to the level of coverage in effect for you and your eligible dependents as of the date of your termination, on a monthly basis on the first business day of the calendar month next following the calendar month in which the applicable COBRA premiums were paid, with respect to the period from the date of your termination until the earlier of (x) twelve (12) months following such date and (y) the date you become eligible for coverage under a subsequent employer’s medical plan.

In the event of a Change in Control, all unvested equity awards then held by you (other than the portion of such equity awards that would otherwise have vested during the six month period after the date of such Change in Control (the “Carved Out Equity”)) will become fully vested and exercisable and no longer subject to any restrictions or forfeiture upon such Change in Control. The Carved Out Equity shall, subject to your continued employment with the Company or its successor in such Change in Control, continue to vest over the first six months after the date of the Change in Control in accordance with the vesting schedule in effect prior to the Change in Control. In the event your employment is terminated by the Company (or any successor or assign) without Cause or by you for Good Reason within twelve (12) months immediately following or within thirty (30) days immediately prior to a Change in Control, then, subject to your remaining available to provide consulting services to the Company as reasonably requested by the Board upon reasonable notice and at mutually agreeable times, in addition to the Termination Payment and in lieu of the Severance Benefits, the Company shall provide the following payments and benefits (“CIC Severance Benefits”): (i) continued payment of your base salary at the then-current rate per pay period,

Notwithstanding anything to the contrary in the foregoing, you will not be entitled to receive any severance payments unless, within sixty (60) days following the date of termination, you, or in the event of your death or Disability, your legal representatives, have executed a general release of all known and unknown claims and covenant not to ▇▇▇ in the form attached hereto as Exhibit A (with such changes to form to help ensure enforceability in light of changes in applicable law).

The Severance Benefits or CIC Severance Benefits, as applicable shall be paid or commence on the first payroll period following the date the release becomes effective (the “Payment Date”); provided, that if the period during which you may deliver the release required by the preceding sentence spans two calendar years, the Payment Date shall be no earlier than January 1 of the second calendar year.

Definitions.

For purposes of this Agreement, “Change in Control” means the consummation of (i) the dissolution or liquidation of the Company; (ii) the sale of all or substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity; (iii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding voting power immediately prior to such transaction do not own a majority of the outstanding voting power of the surviving or resulting entity (or its ultimate parent, if applicable); (iv) the acquisition of all or a majority of the outstanding voting stock of the Company in a single transaction or a series of related transactions by a Person or group of Persons; or (v) any other acquisition of the business of the Company, as determined by the Board; provided, however, that the Company’s Initial Public Offering, any subsequent public offering or anther capital raising event, or a merger effected solely to change the Company’s domicile shall not constitute a “Change in Control”.

As used herein, “Cause” means: (i) a willful and material act of dishonesty by you in connection with the performance of your duties as an employee of the Company; (ii) your conviction of, or plea of guilty or nolo contendere to, a felony or any crime involving fraud, embezzlement or any willful act of moral turpitude, or a material violation of a federal or state law by you, that the Board reasonably determines has had or is reasonably likely to have a materially detrimental effect on the Company’s reputation or business; (iii) your gross misconduct in the performance of your duties as an employee of the Company; (iv) your willful and material unauthorized use or disclosure of any proprietary information or trade secrets of the Company that materially damages the Company or any other party to whom you owe an obligation of nondisclosure as a result of your relationship with the Company; (v) your willful and material breach of any obligations under any written agreement or covenant with the Company, including this Agreement; or (vi) your continued willful and substantial failure to perform your employment duties (other than a result of your death or Disability) after notice. Cause shall not exist unless, in any case, you have first received a written notice from the Board that sets forth the factual basis for the Board’s determination as to any behavior or occurrence claimed as Cause and you fail to cure such claimed behavior or occurrence, if curable, to the reasonable satisfaction of a majority of the Board within ten (10) business days after receiving such written notice, in which case your termination date will be the expiration date of the cure period, if any. For purposes of this paragraph, no act or failure to act on your part shall be considered “willful” unless it is done or omitted to be done by you in bad faith and without reasonable belief that the act or failure to act was in the best interest of the Company.

As used herein, “Code” means the Internal Revenue Code of 1986, as amended.

As used herein, “Disability” means “disability” as defined in Section 422 of the Code.

As used herein, “Good Reason” means the occurrence of one or more of the following, without your written consent: (i) a material reduction in your base salary or target annual bonus; (ii) a material diminution of your title, duties, responsibilities or reporting lines (it being understood that your ceasing to be a member of the Board as a result of the failure by the Company’s stockholders to elect or reelect you to such position shall not constitute Good Reason hereunder); (iii) a material change in the principal geographic location at which you must perform services, more than fifty (50) miles from the Company’s head office; or (iv) a material breach by the Company of this Agreement or any equity award agreement between you and the Company. Any such event shall not constitute Good Reason unless and until you have provided the Company with written

As used herein, “Initial Public Offering” means the consummation of the first firm commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, covering the offer and sale by the Company of its equity securities, as a result of or following which the common stock of the Company shall be publicly held.

As used herein, “Person” means any individual, corporation, partnership (limited or general), limited liability company, limited liability partnership, association, trust, joint venture, unincorporated organization or any similar entity.

Indemnification. The Company shall indemnify you and hold you harmless to the fullest extent provided under the Certificate of Incorporation and the By-Laws of the Company against and in respect of any and all actions, suits, proceedings, claims, demands, judgments, costs, expenses (including reasonable attorney’s fees), losses, and damages resulting from your good faith performance of your duties and obligations to the Company, subject to the limitations and conditions set forth therein. This obligation shall survive the termination of your employment with the Company. From and after the Effective Date, the Company shall cover you under directors’ and officers’ liability insurance both during and, while potential liability exists, after your cessation of service to the Company in the same amount and to the same extent as the Company covers its other executive officers and directors.

Timing of Payments and Section 409A.

Notwithstanding anything to the contrary in this Agreement, if at the time your employment terminates, you are a “specified employee,” as defined below, any and all amounts payable under this Agreement on account of such separation from service that would (but for this provision) be payable within six (6) months following the date of termination, shall instead be paid on the next business day following the expiration of such six (6)-month period or, if earlier, upon your death; except (A) to the extent of amounts that do not constitute a deferral of compensation within the meaning of Treasury regulation Section 1.409A-1(b) (including without limitation by reason of the safe harbor set forth in Section 1.409A-1 (b)(9)(iii), as determined by the Company in its reasonable good faith discretion); (B) benefits which qualify as excepted welfare benefits pursuant to Treasury regulation Section 1.409A-1(a)(5); or (C) other amounts or benefits that are not subject to the requirements of Section 409A of the Code (“Section 409A”).

For purposes of this Agreement, all references to “termination of employment” and correlative phrases shall be construed to require a “separation from service” (as defined in Section 1.409A-1(h) of the Treasury regulations after giving effect to the presumptions contained therein), and the term “specified employee” means an individual determined by the Company to be a specified employee under Treasury regulation Section 1.409A-l(i).

Each payment made under this Agreement shall be treated as a separate payment and the right to a series of installment payments under this Agreement is to be treated as a right to a series of separate payments.

In no event shall the Company have any liability relating to the failure or alleged failure of any payment or benefit under this Agreement to comply with, or be exempt from, the requirements of Section 409A.

Section 280G.

Notwithstanding anything to the contrary contained in this Agreement, to the extent that any of the payments and benefits provided for under this Agreement or any other agreement or arrangement between the Company and you (collectively, the “Payments”) (i) constitute a “parachute payment” within the meaning of Section 280G of the Code and (ii) but for this paragraph, would be subject to the excise tax imposed by Section 4999 of the Code, then the Payments shall be reduced to the extent necessary so that no portion of such Payments retained by you shall be subject to excise tax under Section 4999 of the Code; provided, however, such reduction shall only occur if after taking into account the applicable federal, state and local income taxes and the excise tax imposed by Section 4999, such reduction results in your receipt on an after-tax basis, of the greatest amount of benefits under this Agreement, notwithstanding that all or some portion of such benefits may be taxable under Section 4999 of the Code. In the event of a determination that such reduction is to take place, reduction shall occur in the following order: first, reduction of cash payments, which shall occur in reverse chronological order such that the cash payment owed on the latest date following the occurrence of the event triggering such excise tax will be the first cash payment to be reduced; second, cancellation of accelerated vesting of equity awards, which shall occur in the reverse order of the date of grant for such stock awards (i.e., the vesting of the most recently granted stock awards will be reduced first); and third, reduction of employee benefits, which shall occur in reverse chronological order such that the benefit owed on the latest date following the occurrence of the event triggering such excise tax will be the first benefit to be reduced. If two or more equity awards are granted on the same date, each award will be reduced on a pro-rata basis.

Unless you and the Company otherwise agree in writing, any determination required under this Section 9 shall be made in writing by a nationally recognized independent public accountanting or consulting firm (the “Accountants”), whose determination shall be conclusive and binding upon you and the Company for all purposes. For purposes of making the calculations required by this Section 9, the Accountants may make reasonable assumptions and approximations concerning

Miscellaneous.

Nothing in this Agreement shall be construed as an agreement, either express or implied, to pay you any compensation or grant you any benefit beyond the end of your employment with the Company, except as otherwise explicitly set forth herein. Your employment and this Agreement will be governed by the laws of the Commonwealth of Massachusetts, without reference to conflicts of laws principles which would result in the application of the law of any other jurisdiction.

You represent that you are not bound by any employment contract, restrictive covenant or other restriction preventing you from entering into employment with or carrying out your responsibilities for the Company, or which is in any way inconsistent with the terms of this Agreement.

You hereby agree to the provisions relating to Intellectual Property and Confidential Information attached as Exhibit B hereto as if such provisions were fully set forth herein. Notwithstanding any other provision in any agreement between you and the Company, Company Confidential Information shall not include any information that (i) is or becomes generally used in the industry or publicly available through lawful means and absent any wrongful conduct by you or others; (ii) any information that was known by you or lawfully in your possession prior to your employment with the Company; and (iii) is independently developed or lawfully disclosed to you by a third party that is unrelated to the Company and is not bound by obligations of confidentiality to the Company with respect to such information.

All notices or other communications required or permitted to be given under this Agreement shall be in writing and shall be deemed to have been duly given when delivered personally or one business day after being sent by a nationally recognized overnight delivery service, charges prepaid. Notices also may be given electronically via PDF and shall be effective on the date transmitted if confirmed within forty eight (48) hours thereafter by a signed original sent in the manner provided in the preceding sentence. Notice to you shall be sent to your most recent residence and personal email address on file with the Company. Notice to the Company shall be sent to its principal place of business and addressed to the Chairperson of the Board, or at the email address provided by the Company for such person.

This Agreement constitutes the entire agreement and understanding between the parties as to the subject matter herein and supersedes all prior or contemporaneous agreements whether written or oral, including, without limitation, the Offer Letter by and between you and the Company, dated January 8, 2018. The terms of this Agreement may only be modified in a specific writing signed by you and an authorized representative of the Company. The invalidity or unenforceability of any provision or provisions of this Agreement will not affect the validity or enforceability of any other provision hereof, which will remain in full force and effect. In the event of any conflict between any of the terms in this Agreement and the terms of any other agreement between you and the Company, the terms of this Agreement will control. This Agreement may be executed in any number of counterparts, all of which taken together shall constitute one instrument. Execution and delivery of this Agreement by facsimile or other electronic signature is legal, valid and binding for all purposes.