Employment Letter Agreement, dated February 5, 2020, by and between David M. Chacko, M.D. and the Registrant

Restated Employment Offer Letter

BASE SALARY. You will receive an annual base salary of $314,000, which reflects a merit increase effective January 1, 2020, for all hours worked, to be paid in accordance with the Company’s customary payroll procedures.

STOCK OPTIONS. You were previously granted stock options to purchase 875,000 shares of the Company’s common stock at an exercise price per share equal to the fair market value per share of the Company’s common stock on the date of grant (the “Stock Options”). The Stock Options were granted pursuant to the Company’s equity incentive plan (the “Plan”). The Stock Options are subject to the terms and conditions of the Plan and your stock option agreement. The Stock Options will vest over a four year vesting schedule, with 25% of the Stock Options vesting on the first anniversary of your commencement of employment and the remaining Stock Options vesting in 36 equal monthly installments thereafter, subject to your continued employment or service to the Company on each such vesting date.

ANNUAL BONUS. Commencing in 2020, the Board has established an annual bonus plan, pursuant to which will be eligible to participate, subject to the terms and conditions of such plan, and your bonus target will be equal to 30% of your base salary (your “Target Bonus”). You must be employed by the Company on the date of payment of such annual bonus in order to be eligible to receive such annual bonus. You hereby acknowledge and agree that nothing contained herein confers upon you any right to an annual bonus in any year, and that whether the Company pays you an annual bonus and the amount of any such annual bonus will be determined by the Company in its sole discretion.

BENEFITS. You shall be eligible to participate in all of the employee benefit plans or programs the Company generally makes available to similarly situated employees, pursuant to the terms and conditions of such plans. You will initially be entitled to 18 days of paid time off each year, accruing on a semi-monthly basis, and all holidays observed by the Company each year. The Company reserves the right to change compensation and benefits provided to its employees from time to time in its discretion.

WITHHOLDING. All amounts payable to you will be subject to appropriate payroll deductions and withholdings.

ACCRUED OBLIGATIONS. If your employment terminates for any reason, you are entitled to your fully earned but unpaid base salary, through the date such termination is effective at the rate then in effect, and all other amounts or benefits to which you are entitled under any compensation, retirement or benefit plan of the Company at the time of your termination of employment in accordance with the terms of such plans, including, without limitation, any accrued but unpaid paid time off and any continuation of benefits required by applicable law (the “Accrued Obligations”).

NON-CIC SEVERANCE BENEFITS. In addition to your Accrued Obligations, subject to your continued compliance with the Proprietary Information and Inventions Agreement, as described below, and the effectiveness of your Release (as defined below), if your employment is involuntarily terminated by the Company without Cause (as defined below) (and other than by reason of your death or disability) or you resign for Good Reason (as defined below) (either such termination, a “Qualifying Termination”), and such Qualifying Termination does not occur during the Change in Control Period (as defined below), you shall be entitled to receive, as the sole severance benefits to which you are entitled, the benefits provided below (the “Non-CIC Severance Benefits”):

An amount equal to your base salary for the Non-CIC Severance Period (as defined below) (at the rate in effect immediately prior to the date of your termination of employment), payable in a lump sum on the first regularly-scheduled payroll date following the date your Release becomes effective (but in no event more than 75 days following your termination date).

For the Non-CIC Severance Period (or, if earlier, the date on which the applicable continuation period under the Consolidated Omnibus Budget Reconciliation Act of 1985, as amended (“COBRA”) expires) (the “COBRA Coverage Period”), if you and/or your eligible dependents who were covered under the Company’s health insurance plans as of the date of your termination of employment elect to have COBRA coverage and are eligible for such coverage, the Company shall pay for or reimburse you on a monthly basis for an amount equal to (a) the monthly premium you and/or your covered dependents, as applicable, are required to pay for continuation coverage pursuant to COBRA for you and/or your eligible dependents, as applicable, who were covered under the Company’s health plans as of the date of your termination of employment (calculated by reference to the premium as of the date of your termination of employment) less (b) the amount you would have had to pay to receive group health coverage for you and/or your covered dependents, as applicable, based on the cost sharing levels in effect on the date of your termination of employment. If any of the Company’s health benefits are self-funded as of the date of your termination of employment, or if the Company cannot

provide the foregoing benefits in a manner that is exempt from Section 409A of the Internal Revenue Code of 1986, as amended (the “Code”), or that is otherwise compliant with applicable law (including, without limitation, Section 2716 of the Public Health Service Act), instead of providing the payments or reimbursements as set forth above, the Company shall instead pay to you the foregoing monthly amount as a taxable monthly payment for the COBRA Coverage Period (or any remaining portion thereof). You shall be solely responsible for all matters relating to continuation of coverage pursuant to COBRA, including, without limitation, the election of such coverage and the timely payment of premiums. You shall notify the Company immediately if you become eligible to receive the equivalent or increased healthcare coverage by means of subsequent employment or self-employment.

CIC SEVERANCE BENEFITS. In addition to your Accrued Obligations, subject to your continued compliance with the Proprietary Information and Inventions Agreement, as described below, and the effectiveness of your Release, if your Qualifying Termination occurs during the Change in Control Period, you shall be entitled to receive, as the sole severance benefits to which you are entitled and in lieu of any Non-CIC Severance Benefits, the benefits provided below (the “CIC Severance Benefits”) (and for the avoidance of doubt, in no event will you be entitled to both the Non-CIC Severance Benefits and the CIC Severance Benefits):

An amount equal to your base salary for the CIC Severance Period (as defined below) (at the rate in effect immediately prior to the date of your termination of employment), payable in a lump sum on the first regularly-scheduled payroll date following the date your Release becomes effective (but in no event more than 75 days following your termination date).

An amount equal to (a) (i) your Target Bonus for the year in which your date of termination occurs, divided by (ii) 12, multiplied by (b) the number of months in the CIC Severance Period, payable in a lump sum on the first regularly-scheduled payroll date following the date your Release becomes effective (but in no event more than 75 days following your termination date).

For the CIC Severance Period (or, if earlier, the date on which the applicable continuation period under COBRA expires) (the “CIC COBRA Coverage Period”), if you and/or your eligible dependents who were covered under the Company’s health insurance plans as of the date of your termination of employment elect to have COBRA coverage and are eligible for such coverage, the Company shall pay for or reimburse you on a monthly basis for an amount equal to (a) the monthly premium you and/or your covered dependents, as applicable, are required to pay for continuation coverage pursuant to COBRA for you and/or your eligible dependents, as applicable, who were covered under the Company’s health plans as of the date of your termination of employment (calculated by reference to the premium as of the date of your termination of employment) less (b) the amount you would have had to pay to receive group health coverage for you and/or your covered dependents, as applicable, based on the cost sharing levels in effect on the date of your termination of employment. If any of the Company’s health benefits are self-funded as of the date of your termination of employment, or if the Company cannot provide the foregoing benefits in a manner that is exempt from Section 409A of the Code, or that is otherwise compliant with applicable law (including, without limitation, Section 2716 of the Public Health Service Act), instead of providing the payments or reimbursements as set forth above, the Company shall instead pay to you the foregoing monthly amount as a taxable monthly payment for the CIC COBRA Coverage Period (or any remaining portion thereof). You shall be solely responsible for all matters relating to continuation of coverage pursuant to COBRA, including, without limitation, the election of such coverage and the timely payment of premiums. You shall notify the Company immediately if you become eligible to receive the equivalent or increased healthcare coverage by means of subsequent employment or self-employment.

Notwithstanding anything else set forth herein, in the Plan or in any award agreement, any unvested Stock Awards (as defined below) then held by you (including the Stock Options) will vest on the effective date of your Release. The foregoing provisions are hereby deemed to be a part of each Stock Award and to supersede any less favorable provision in any agreement or plan regarding such Stock Award.

As a condition to your receipt of any post-termination payments and benefits pursuant to the preceding paragraphs, you shall execute and not revoke a general release of all claims in favor of the Company (the “Release”) in a form reasonably acceptable to the Company. In the event the Release does not become effective within the 60-day period following the date of your termination of employment, you will not be entitled to the aforesaid payments and benefits.

For purposes of this Amended Agreement, “Cause” means any of the following: (a) your commission of an act of fraud, embezzlement or dishonesty, or the commission of some other illegal act by you, that has a demonstrable adverse impact on the Company or any successor or affiliate thereof; (b) your conviction of, or plea of “guilty” or “no contest” to, a felony or any crime involving fraud, dishonesty or moral turpitude under the laws of the United States or any state thereof; (c) any intentional, unauthorized use or disclosure by you of confidential information or trade secrets of the Company or any successor or affiliate thereof; (d) your gross negligence, insubordination or material violation of any duty of loyalty to the Company or any successor or affiliate thereof, or any other demonstrable material misconduct on your part; (e) your ongoing and repeated failure or refusal to perform or neglect of your duties as required by this Amended Agreement or your ongoing and repeated failure or refusal to comply with the instructions given to you by the Chief Executive Officer of the Company or the Board, which failure, refusal or neglect continues for 15 days following your receipt of written notice from the Chief Executive Officer of the Company or the Board stating with specificity the nature of such failure, refusal or neglect; or (f) your willful, material breach of any Company policy or any material provision of this Amended Agreement or the Proprietary Information and Inventions Agreement. Prior to the determination that “Cause” under clauses (d), (e) or (f) has occurred, the Company shall (i) provide to you in writing, in reasonable detail, the reasons for the determination that such “Cause” exists, (ii) other than with respect to clause (e) above which specifies the applicable period of time for you to remedy your breach, afford you a reasonable opportunity to remedy any such breach, (iii) provide you an opportunity to be heard prior to the final decision to terminate your employment hereunder for such “Cause” and (iv) make any decision that such “Cause” exists in good faith. The foregoing definition shall not in any way preclude or restrict the right of the Company or any successor or affiliate thereof to discharge or dismiss you for any other acts or omissions, but such other acts or omissions shall not be deemed, for purposes of this Amended Agreement, to constitute grounds for termination for Cause.

For purposes of this Amended Agreement, “Change in Control” means (a) a merger or consolidation of the Company with or into any other corporation or other entity or person, (b) a sale, lease, exchange or other transfer in one transaction or a series of related transactions of all or substantially all of the Company’s assets, or (c) any other transaction, including the sale by the Company of new shares of its capital stock or a transfer of existing shares of capital stock of the Company, the result of which is that a third party that is not an affiliate of the Company or its stockholders (or a group of third parties not affiliated with the Company or its stockholders) immediately prior to such transaction acquires or holds capital stock of the Company representing a majority of the Company’s outstanding voting power immediately following such transaction; provided that the following events shall not constitute a “Change in Control”: (i) a transaction (other than a sale of all or substantially all of the Company’s assets) in which the holders of the voting securities of the Company immediately prior to the merger or consolidation hold, directly or indirectly, at least a majority of the voting securities in the successor corporation or its parent

immediately after the merger or consolidation; (ii) a sale, lease, exchange or other transaction in one transaction or a series of related transactions of all or substantially all of the Company’s assets to an affiliate of the Company; (iii) an initial public offering of any of the Company’s securities; (iv) a reincorporation of the Company solely to change its jurisdiction; or (v) a transaction undertaken for the primary purpose of creating a holding company that will be owned in substantially the same proportion by the persons who held the Company’s securities immediately before such transaction.

For purposes of this Amended Agreement, “Change in Control Period” means the period commencing on the date of a Change in Control and ending 12 months following such Change in Control.

For purposes of this Amended Agreement, “CIC Severance Period” means (a) if your Qualifying Termination occurs during the Change in Control Period and prior to the first anniversary of your hire date, 3 months; (b) if your Qualifying Termination occurs during the Change in Control Period and on or after the first anniversary of your hire date but prior to the second anniversary of your hire date, 6 months; or (c) if your Qualifying Termination occurs during the Change in Control Period and on or after the second anniversary of your hire date, 9 months.

For purposes of this Amended Agreement, “Good Reason” means any of the following without your written consent: (a) a material diminution in your authority, duties or responsibilities; (b) a material diminution in your base compensation, unless such a reduction is imposed across-the-board to senior management of the Company; (c) a material change in the geographic location at which you must perform your duties; or (d) any other action or inaction that constitutes a material breach by the Company or any successor or affiliate of its obligations to you under this Amended Agreement. You must provide written notice to the Company of the occurrence of any of the foregoing events or conditions without your written consent within 60 days of the occurrence of such event. The Company or any successor or affiliate shall have a period of 30 days to cure such event or condition after receipt of written notice of such event from you. Your termination of employment by reason of resignation from employment with the Company for Good Reason must occur within 30 days following the expiration of the foregoing 30-day cure period.

For purposes of this Amended Agreement, “Non-CIC Severance Period” means, provided your Qualifying Termination does not occur during the Change in Control Period, (a) if your Qualifying Termination occurs prior to the first anniversary of your hire date, 2 months; (b) if your Qualifying Termination occurs on or after the first anniversary of your hire date but prior to the second anniversary of your hire date, 4 months; or (c) if your Qualifying Termination occurs on or after the second anniversary of your hire date, 6 months.

For purposes of this Amended Agreement, “Stock Awards” means all stock options, restricted stock and such other awards granted pursuant to the Plan or the Company’s other stock option and equity incentive award plans or agreements, as in effect from time to time, and any shares of stock issued upon exercise or settlement thereof, including the Stock Options.

To the extent applicable, this Amended Agreement shall be interpreted in accordance with Section 409A of the Code and Department of Treasury regulations and other interpretive guidance issued thereunder. The intent of the parties is that payments and benefits under this Amended Agreement comply with, or be exempt from Section 409A of the Code and, accordingly, to the maximum extent permitted, this Amended Agreement shall be interpreted to be in compliance with such intention. To the extent that any provision in this Amended Agreement is ambiguous as to its compliance with or exemption from Section 409A of the Code, the provision shall be read in such a manner that no payments payable under this Amended Agreement shall be subject to an “additional tax” as defined in Section 409A(a)(1)(B) of the Code. For purposes of Section 409A of the Code, any right to a series of installment payments under this Amended Agreement shall be treated as a right to a series of separate payments. For

purposes of this Amended Agreement, to the extent that the payments or benefits under this Amended Agreement are “non-qualified deferred compensation” subject to Section 409A of the Code or as otherwise required to ensure such payments or benefits are exempt from or comply with Section 409A of the Code, all references to your “termination of employment” shall mean your “separation from service” (as defined in Treasury Regulation Section 1.409A-1(h)) (“Separation from Service”). If you are a “specified employee” (as defined in Section 409A of the Code), as determined by the Company in accordance with Section 409A of the Code, on the date of your Separation from Service, to the extent that the payments or benefits under this Amended Agreement are “non-qualified deferred compensation” subject to Section 409A of the Code and the delayed payment or distribution of all or any portion of such amounts to which you are entitled under this Amended Agreement is required in order to avoid a prohibited distribution under Section 409A(a)(2)(B)(i) of the Code, then such portion deferred pursuant to this paragraph shall be paid or distributed to you in a lump sum on the earlier of (a) the date that is 6 months and one day following your Separation from Service, (b) the date of your death or (c) the earliest date as is permitted under Section 409A of the Code. Any remaining payments due under this Amended Agreement shall be paid as otherwise provided herein.

To the extent that the payments or benefits under this Amended Agreement are “non-qualified deferred compensation” subject to Section 409A of the Code, if the period during which you may deliver the Release required hereunder spans two calendar years, the payment of your post-termination benefits shall occur on the later of (a) January 1 of the second calendar year, or (b) the first regularly-scheduled payroll date following the date your Release becomes effective.

Any reimbursement of expenses or in-kind benefits payable under this Amended Agreement shall be made in accordance with Treasury Regulation Section 1.409A-3(i)(1)(iv) and shall be paid on or before the last day of your taxable year following the taxable year in which you incurred the expenses. The amount of expenses reimbursed or in-kind benefits payable in one year shall not affect the amount eligible for reimbursement or in-kind benefits payable in any other taxable year of yours, and your right to reimbursement for such amounts shall not be subject to liquidation or exchange for any other benefit.

In the event that any payment or benefit received or to be received by you pursuant to the terms of any plan, arrangement or agreement (including any payment or benefit received in connection with a change of control or the termination of your employment) (all such payments and benefits being hereinafter referred to as the “Total Payments”) would be subject (in whole or part) to the excise tax (the “Excise Tax”) imposed under Section 4999 of the Code, then the Total Payments shall be reduced to the extent necessary so that no portion of the Total Payments is subject to the Excise Tax but only if (a) the net amount of such Total Payments, as so reduced (after subtracting the amount of federal, state and local income taxes on such reduced Total Payments and after taking into account the phase out of itemized deductions and personal exemptions attributable to such reduced Total Payments) is greater than or equal to (b) the net amount of such Total Payments without such reduction (after subtracting the net amount of federal, state and local income taxes on such Total Payments and the amount of Excise Tax to which you would be subject in respect of such unreduced Total Payments and after taking into account the phase out of itemized deductions and personal exemptions attributable to such unreduced Total Payments); provided, however, that this sentence shall not apply if, immediately before the change in ownership or control on which such Total Payments are contingent or otherwise relate, no stock in the Company is readily tradeable on an established securities market or otherwise (as determined in accordance with Treasury Reg. Section 1.280G-1 Q&A 6). The Total Payments shall be reduced in the following order: (i) reduction of any cash severance payments otherwise payable to you that are exempt from Section 409A of the Code, (ii) reduction of any other cash payments or benefits otherwise payable to you that are exempt from Section 409A of the Code, but excluding any payment attributable to the acceleration of vesting or payment with respect to

any equity award with respect to the Company’s common stock that is exempt from Section 409A of the Code, (iii) reduction of any other payments or benefits otherwise payable to you on a pro-rata basis or such other manner that complies with Section 409A of the Code, but excluding any payment attributable to the acceleration of vesting and payment with respect to any equity award with respect to the Company’s common stock that is exempt from Section 409A of the Code, and (iv) reduction of any payments attributable to the acceleration of vesting or payment with respect to any equity award with respect to the Company’s common stock that is exempt from Section 409A of the Code; provided, in case of clauses (ii), (iii) and (iv), that reduction of any payments or benefits attributable to the acceleration of vesting of Company equity awards shall be first applied to Company equity awards that would otherwise vest last in time. The foregoing reductions shall be made in a manner that results in the maximum economic benefit to you on an after-tax basis and, to the extent economically equivalent payments or benefits are subject to reduction, in a pro rata manner.

All determinations regarding the application of this “Section 280G Treatment” section shall be made by an accounting firm or consulting group with nationally recognized standing and substantial expertise and experience in performing calculations regarding the applicability of Section 280G of the Code and the Excise Tax retained by the Company prior to the date of the applicable change in control (the “280G Firm”). For purposes of determining whether and the extent to which the Total Payments will be subject to the Excise Tax, (a) no portion of the Total Payments shall be taken into account which, in the written opinion of the 280G Firm, (i) does not constitute a “parachute payment” within the meaning of Section 280G(b)(2) of the Code (including by reason of Section 280G(b)(4)(A) of the Code) and, in calculating the Excise Tax, or (ii) constitutes reasonable compensation for services actually rendered, within the meaning of Section 280G(b)(4)(B) of the Code, in excess of the “base amount” (as defined in Section 280G(b)(3) of the Code) allocable to such reasonable compensation, (b) no portion of the Total Payments the receipt or enjoyment of which you shall have waived at such time and in such manner as not to constitute a “payment” within the meaning of Section 280G(b) of the Code shall be taken into account, and (c) the value of any non-cash benefit or any deferred payment or benefit included in the Total Payments shall be determined by the 280G Firm in accordance with the principles of Sections 280G(d)(3) and (4) of the Code. All determinations related to the calculations to be performed pursuant to this this “Section 280G Treatment” section shall be done by the 280G Firm.

The 280G Firm will be directed to submit its determination and detailed supporting calculations to both you and the Company within 15 days after notification from either the Company or you that you may receive payments which may be “parachute payments.” You and the Company will each provide the 280G Firm access to and copies of any books, records, and documents in their possession as may be reasonably requested by the 280G Firm, and otherwise cooperate with the 280G Firm in connection with the preparation and issuance of the determinations and calculations contemplated by this Amended Agreement. The fees and expenses of the 280G Firm for its services in connection with the determinations and calculations contemplated by this Amended Agreement will be borne by the Company.

Notwithstanding the foregoing, if any portion of the Total Payments would not be subject to the Excise Tax if the stockholder approval requirements of Section 280G(b)(5) of the Code are satisfied, subject to your waiver of the rights to such portion of the Total Payments in accordance with and to the extent required by Section 280G of the Code with respect to any portion of the Total Payments that would otherwise be subject to excise tax imposed by Section 4999 of the Code (before giving effect to any reduction in the Total Payments contemplated above), the Company shall use its reasonable best efforts to cause such payments to be submitted for such approval prior to the event giving rise to such payments. To the extent the Company submits any payment or benefit payable to you under this Amended Agreement or otherwise to the Company’s stockholders for approval in accordance with Treasury Reg. Section 1.280G-1 Q&A 7, the foregoing provisions under this “Section 280G Treatment” section shall not apply following such submission and such payments and benefits will be treated in accordance with the results of such vote, except that any reduction in, or waiver of, such payments or benefits required by such vote will be applied without any application of discretion by you and in the order prescribed in the preceding paragraph.

/s/ David Chacko

Date: 

March 20, 2020