Severance Agreement dated August 7, 2019 by and between the Registrant and Dr. Leslie Sloan

Term of Agreement.

The date the Executive’s employment with the Company terminates for a reason other than a Qualifying Termination or CIC Qualifying Termination, or

The date the Company has met all of its obligations under this Agreement following a termination of the Executive’s employment with the Company due to a Qualifying Termination or CIC Qualifying Termination.

Severance Benefits. The Company or its subsidiaries shall pay the Executive (i) 12 months of her monthly base salary, (ii) one-hundred percent (100%) of the Executive’s annual target bonus (in each case, at the rate in effect immediately prior to the actions that resulted in the Qualifying Termination).  The severance benefits shall be paid through salary continuation in equal installments in accordance with the Company’s or its subsidiary’s, as applicable, standard payroll procedures, with the initial payment to occur on the first payroll date following the sixtieth (60^th) day following the Separation, with the first installment to include a catchup payment for amounts covering the period from the date of Separation through the first payment date, provided that the Release Conditions have been satisfied. However, if the period comprising the sum of the sixty (60)-day period described in the preceding sentence and the ten (10)-day period described in Section 7(e)(3) below spans two calendar years, then the payments which constitute deferred compensation subject to Section 409A will not in any case commence in the first calendar year. The period between the date of Executive’s Separation and final severance payment shall be referred to herein as the “Severance Period.”

Continued Employee Benefits. If Executive timely elects continued coverage under the Consolidated Omnibus Budget Reconciliation Act (“COBRA”), the Company or its subsidiary shall pay the full amount of Executive’s COBRA premiums on behalf of the Executive for the Executive’s continued coverage under the Company’s or its subsidiary’s, as applicable, health, dental and vision plans, including coverage for the Executive’s eligible dependents, for the Severance Period. Notwithstanding the foregoing, if the Company, in its sole discretion, determines that it cannot provide the foregoing subsidy of COBRA coverage without potentially

violating or causing the Company or its subsidiary to incur additional expense as a result of noncompliance with applicable law (including, without limitation, Section 2716 of the Public Health Service Act), the Company or its subsidiary instead shall provide to Executive a taxable monthly payment in an amount equal to the monthly COBRA premium that Executive would be required to pay to continue the group health coverage in effect on the date of the Separation (which amount shall be based on the premium for the first month of COBRA coverage), which payments shall be made regardless of whether Executive elects COBRA continuation coverage and shall commence on the later of (i) the first day of the month following the month in which Executive experiences a Separation and (ii) the effective date of the Company’s determination of violation of applicable law, and shall end on the earlier of (x) the effective date on which Executive becomes covered by a health, dental or vision insurance plan of a subsequent employer, and (y) the last day of the Severance Period, provided that, any taxable payments under this Section 2(b) will not be paid before the first business day occurring after the sixtieth (60^th) day following the Separation and, once they commence, will include any unpaid amounts accrued from the date of Executive’s Separation (to the extent not otherwise satisfied with continuation coverage). However, if the period comprising the sum of the sixty (60)-day period described in the preceding sentence and the ten (10)-day period described in Section 7(e)(3) below spans two calendar years, then the payments which constitute deferred compensation subject to Section 409A will not in any case be paid in the first calendar year. Executive shall have no right to an additional gross-up payment to account for the fact that such COBRA premium amounts are paid on an after-tax basis.

Equity. Any outstanding Equity Awards, including awards that would otherwise vest only upon satisfaction of performance criteria, shall accelerate and become vested and exercisable as if an additional twelve (12) months of vesting had occurred to the then-unvested shares subject to the Equity Award.  Equity Awards subject to performance-based vesting criteria as of the date of the Separation shall accelerate and become vested and exercisable as to the number of shares subject to such Equity Award that would have vested if Executive had completed an additional twelve (12) months of service following the date of Separation, provided, however, that the vesting of such performance-based awards shall be as if all applicable performance criteria were achieved at target levels during such 12-month period.  Subject to Section 4, the accelerated vesting described above shall be effective as of the Separation.

Severance Benefits. The Company or its subsidiary shall pay the Executive the severance benefits set forth in Section 2(a) above.

Continued Employee Benefits. The Company or its subsidiary shall pay the Executive the continued employee benefits set forth in Section 2(b) above for the same period that the Executive is paid severance benefits pursuant to Section 3(a) following the Executive’s Separation or, if earlier, until Executive becomes covered by a health, dental or vision insurance plan of a subsequent employer or until Executive is no longer eligible for COBRA benefits.

Equity. Each of Executive’s then outstanding Equity Awards, including awards that would otherwise vest only upon satisfaction of performance criteria, shall accelerate and become vested and exercisable as to 100% of the then unvested shares underlying the Equity Award. For awards that would otherwise vest only upon satisfaction of performance criteria, the foregoing acceleration shall be based on achievement of performance criteria at target, except to the extent otherwise provided in the award agreement evidencing such award. “Equity Awards” means all options to purchase shares of Company common stock as well as any and all other stock-based awards granted to the Executive, including but not limited to stock bonus awards, restricted stock, restricted stock units or stock appreciation rights. Subject to Section 4, the accelerated vesting described above shall be effective as of the Separation.

Covenants.

Non-Competition. The Executive agrees that the benefits provided in this Agreement are granted in consideration for the ongoing promises and obligations of Executive under her employment agreement and any amendments thereto, including but not limited to Executive’s obligations concerning non-competition and non-solicitation.

Cooperation and Non-Disparagement. The Executive agrees that, during the Severance Period, he or she shall cooperate with the Company or its subsidiary in every reasonable respect and shall use his or her best efforts to assist the Company or its subsidiary with the transition of Executive’s duties to his or her successor. The Executive further agrees that following the date of Separation, he or she shall not in any way or by any means disparage the Company, its subsidiaries, or the members of their Board of Directors or their officers and employees.

Definitions.

“Cause” means (i) an unauthorized use or disclosure by Executive of the Company’s or its subsidiaries’ confidential information or trade secrets, which use or disclosure causes or is reasonably likely to cause material harm to the Company or its subsidiaries, (ii) a material breach of any agreement between Executive and the Company or its subsidiaries, (iii) a material failure to comply with the Company’s or its subsidiaries’ written policies or rules that has caused or is reasonably likely to cause material injury to the Company, its successor, or its affiliates, or any of their business, (iv) conviction of, or plea of “guilty” or “no contest” to, a felony under the laws of the United States or any state thereof, (v) willful misconduct that has caused or is reasonably likely to cause material injury to the Company, its successor, or its affiliates, or any of their business, (vi) embezzlement, (vii) failure to cooperate with the Company or its subsidiaries in any investigation or formal proceeding if the Company or its subsidiary, as applicable, has requested Executive’s reasonable cooperation, (viii) violation of any applicable federal, state or foreign statutes or laws that govern or regulate employment, pharmaceutical drugs or securities, including but not limited to the laws enforced by the federal Equal Employment Opportunity Commission, Department of Labor, Food and Drug Administration, Securities and Exchange Commission and Department of Justice or (ix) a continued failure to perform assigned duties after receiving written notification of such failure from the Company’s or its subsidiarys’, as applicable, Chief Executive Officer; provided that Executive must be provided with written notice of Executive’s termination for “Cause” and Executive must be provided with a thirty (30) day period following Executive’s receipt of such notice to cure the event(s) that trigger “Cause,” with the Company’s or its subsidiarys’, as applicable, Board of Directors making the final determination whether Executive has cured any Cause.

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

“Change in Control.” For all purposes under this Agreement, a Change in Control shall mean a “Corporate Transaction,” as such term is defined in the Company’s 2015 Equity Incentive Plan, as may be amended from time to time, provided that the transaction (including any series of transactions) also qualifies as a change in control under U.S. Treasury Regulation 1.409A-3(i)(5)(v) or 1.409A-3(i)(5)(vii).

“CIC Qualifying Termination” means a Separation (A) within twelve (12) months following a Change in Control or (B) within three (3) months preceding a Change in Control (but as to part (B), only if the Separation occurs after a Potential Change in Control) resulting, in either case (A) or (B), from (i) the Company or its subsidiary, as applicable, terminating the Executive’s employment for any reason other than Cause or (ii) the Executive voluntarily resigning his or her employment for Good Reason. A termination or resignation due to the Executive’s death or disability shall not constitute a CIC Qualifying Termination. A “Potential Change in Control” means the date of execution of a legally binding and definitive agreement for a corporate transaction which, if consummated, would constitute the applicable Change in Control (which for the avoidance of doubt, would include a merger agreement, but not a term sheet for a merger agreement). In the case of a termination following a Potential Change in Control and before a Change in Control, solely for purposes of benefits under this Agreement, the date of Separation will be deemed the date the Change in Control is consummated.

“Good Reason” means, without the Executive’s consent, (i) a material reduction in the Executive’s level of responsibility and/or scope of authority, (ii) a reduction by more than 10% in Executive’s base salary (other than a reduction generally applicable to executive officers of the Company or its subsidiary, as applicable, and in generally the same proportion as for the Executive), or (iii) relocation of the Executive’s principal workplace by more than thirty-five (35) miles from Executive’s then current place of employment. For the purpose of clause (i), a change in responsibility shall not be deemed to occur (A) solely because Executive is part of a larger organization or (B) solely because of a change in title. For the Executive to receive the benefits under this Agreement as a result of a voluntary resignation under this subsection (e), all of the following requirements must be satisfied: (1) the Executive must provide notice to the Company or its subsidiary, as applicable, of his or her intent to assert Good Reason within sixty (60) days of the initial existence of one or more of the conditions set forth in subclauses (i) through (iii); (2) the Company or its subsidiary, as applicable, will have thirty (30) days (the “Company Cure Period”) from the date of such notice to remedy the condition and, if it does so, the Executive may withdraw his or her resignation or may resign with no benefits; and (3) any termination of employment under this provision must occur within ten (10) days of the earlier of expiration of the Company Cure Period or written notice from the Company or its subsidiary, as applicable, that it will not undertake to cure the condition set forth in subclauses (i) through (iii). Should the Company or its subsidiary, as applicable, remedy the condition as set forth above and then one or more of the conditions arises again within twelve months following the occurrence of a Change in Control, the Executive may assert Good Reason again subject to all of the conditions set forth herein.

“Release Conditions” mean the following conditions: (i) Company has received the Executive’s executed Release and (ii) any rescission period applicable to the Executive’s executed Release has expired.

“Qualifying Termination” means a Separation that is not a CIC Qualifying Termination, but which results from (i) the Company or its subsidiary, as applicable, terminating the Executive’s employment for any reason other than Cause or (ii) the Executive voluntarily resigning his or her employment for Good Reason. A termination or resignation due to the Executive’s death or disability shall not constitute a Qualifying Termination.

“Separation” means a “separation from service,” as defined in the regulations under Section 409A of the Code.

Successors.

Company’s Successors. The Company shall require any successor (whether direct or indirect and whether by purchase, lease, merger, consolidation, liquidation or otherwise) to all or substantially all of the Company’s business and/or assets, by an agreement in substance and form satisfactory to the Executive, to assume this Agreement and to agree expressly to perform this Agreement in the same manner and to the same extent as the Company would be required to perform it in the absence of a succession. For all purposes under this Agreement, the term “Company” shall include any successor to the Company’s business and/or assets or which becomes bound by this Agreement by operation of law.

Executive’s Successors. This Agreement and all rights of the Executive hereunder shall inure to the benefit of, and be enforceable by, the Executive’s personal or legal representatives, executors, administrators, successors, heirs, distributees, devisees and legatees.

Golden Parachute Taxes.

Best After-Tax Result. In the event that any payment or benefit received or to be received by Executive pursuant to this Agreement or otherwise (“Payments”) would (i) constitute a “parachute payment” within the meaning of Section 280G of the Code and (ii) but for this subsection (a), be subject to the excise tax imposed by Section 4999 of the Code, any successor provisions, or any comparable federal, state, local or foreign excise tax (“Excise Tax”), then, subject to the provisions of Section 10, such Payments shall be either (A) provided in full pursuant to the terms of this Agreement or any other applicable agreement, or (B) provided as to such lesser extent which would result in the Payments being $1.00 less than the amount at which any portion of the Payments would be subject to the Excise Tax (“Reduced Amount”), whichever of the foregoing amounts, taking into account the applicable federal, state, local and foreign income, employment and other taxes and the Excise Tax (including, without limitation, any interest or penalties on such taxes), results in the receipt by Executive, on an after-tax basis, of the greatest amount of payments and benefits provided for hereunder or otherwise, notwithstanding that all or some portion of such Payments may be subject to the Excise Tax. Unless the Company and Executive otherwise agree in writing, any determination required under this Section shall be made by independent tax counsel designated by the Company and reasonably acceptable to Executive (“Independent Tax Counsel”), whose determination shall be conclusive and binding upon Executive and the Company for all purposes. For purposes of making the calculations required under this Section, Independent Tax Counsel may make reasonable assumptions and approximations concerning applicable taxes and may rely on reasonable, good faith interpretations concerning the application of Sections 280G and 4999 of the Code; provided that Independent Tax Counsel shall assume that Executive pays all taxes at the highest marginal rate. The Company and Executive shall furnish to Independent Tax Counsel such information and documents as Independent Tax Counsel may reasonably request in order to make a determination under this Section. The Company shall bear all costs that Independent Tax Counsel may reasonably incur in connection with any calculations contemplated by this Section. In the event that Section 9(a)(ii)(B) above applies, then based on the information provided to Executive and the Company by

Independent Tax Counsel, the cutback described hereunder will apply as to compensation not subject to Section 409A of the Code prior to compensation subject to Section 409A of the Code and will otherwise apply on a reverse chronological basis from payments latest in time. If the Internal Revenue Service (the “IRS”) determines that any Payment is subject to the Excise Tax, then Section 9(b) hereof shall apply, and the enforcement of Section 9(b) shall be the exclusive remedy to the Company.

Adjustments. If, notwithstanding any reduction described in Section 9(a) hereof (or in the absence of any such reduction), the IRS determines that Executive is liable for the Excise Tax as a result of the receipt of one or more Payments, then Executive shall be obligated to surrender or pay back to the Company or its subsidiary, as applicable, within one-hundred twenty (120) days after a final IRS determination, an amount of such payments or benefits equal to the “Repayment Amount.” The Repayment Amount with respect to such Payments shall be the smallest such amount, if any, as shall be required to be surrendered or paid to the Company or its subsidiary, as applicable, so that Executive’s net proceeds with respect to such Payments (after taking into account the payment of the Excise Tax imposed on such Payments) shall be maximized. Notwithstanding the foregoing, the Repayment Amount with respect to such Payments shall be zero (0) if a Repayment Amount of more than zero (0) would not eliminate the Excise Tax imposed on such Payments or if a Repayment Amount of more than zero would not maximize the net amount received by Executive from the Payments. If the Excise Tax is not eliminated pursuant to this Section 9(b), Executive shall pay the Excise Tax.

Miscellaneous Provisions.

Section 409A. To the extent (i) any payments to which Executive becomes entitled under this Agreement, or any agreement or plan referenced herein, in connection with Executive’s termination of employment with the Company or its subsidiary, as applicable, constitute deferred compensation subject to Section 409A of the Code and (ii) Executive is deemed at the time of such termination of employment to be a “specified” employee under Section 409A of the Code, then such payment or payments shall not be made or commence until the earlier of (i) the expiration of the six (6)-month period measured from the Executive’s Separation; or (ii) the date of Executive’s death following such Separation; provided, however, that such deferral shall only be effected to the extent required to avoid adverse tax treatment to Executive, including (without limitation) the additional twenty percent (20%) tax for which Executive would otherwise be liable under Section 409A(a)(1)(B) of the Code in the absence of such deferral.Upon the expiration of the applicable deferral period, any payments which would have otherwise been made during that period (whether in a single sum or in installments) in the absence of this paragraph shall be paid to Executive or Executive’s beneficiary in one lump sum (without interest). Except as otherwise expressly provided herein, to the extent any expense reimbursement or the provision of any in-kind benefit under this Agreement (or otherwise referenced herein) is determined to be subject to (and not exempt from) Section 409A of the Code, the amount of any such expenses eligible for reimbursement, or the provision of any in-kind benefit, in one calendar year shall not affect the expenses eligible for reimbursement or in kind benefits to be provided in any other calendar year, in no event shall any expenses be reimbursed after the last day of the calendar year following the calendar year in which Executive incurred such expenses, and in no event shall any right to reimbursement or the provision of any in-kind benefit be subject to liquidation or exchange for another benefit. To the extent that any provision of this Agreement is ambiguous as to its

exemption or compliance with Section 409A, the provision will be read in such a manner so that all payments hereunder are exempt from Section 409A to the maximum permissible extent, and for any payments where such construction is not tenable, that those payments comply with Section 409A to the maximum permissible extent. To the extent any payment under this Agreement may be classified as a “short-term deferral” within the meaning of Section 409A, such payment shall be deemed a short-term deferral, even if it may also qualify for an exemption from Section 409A under another provision of Section 409A. Payments pursuant to this Agreement (or referenced in this Agreement) are intended to constitute separate payments for purposes of Section 1.409A-2(b)(2) of the regulations under Section 409A.

Other Arrangements. This Agreement supersedes Executive’s prior Severance Agreement by and between the Company and Executive, dated July 10, 2017. This Agreement also supersedes any and all cash severance arrangements and vesting acceleration arrangements on change in control under any agreement governing Equity Awards, severance and salary continuation arrangements, programs and plans which were previously offered, or may be offered on the Effective Date or thereafter, by the Company or its subsidiary, as applicable, to the Executive, including change in control severance arrangements and vesting acceleration arrangements pursuant to an agreement governing Equity Awards, employment agreement or offer letter, and Executive hereby waives Executive’s rights to such other benefits. In no event shall any individual receive cash severance benefits under both this Agreement and any other severance pay or salary continuation program, plan or other arrangement with the Company or its subsidiaries. For the avoidance of doubt, in no event shall Executive receive payment under both Section 2 and Section 3 with respect to Executive’s Separation.

Dispute Resolution. To ensure rapid and economical resolution of any and all disputes that might arise in connection with this Agreement, Executive and the Company agree that any and all disputes, claims, and causes of action, in law or equity, arising from or relating to this Agreement or its enforcement, performance, breach, or interpretation, will be resolved solely and exclusively by final, binding, and confidential arbitration, by a single arbitrator, in San Francisco County, and conducted by Judicial Arbitration & Mediation Services, Inc. (“JAMS”) under its then-existing employment rules and procedures. Nothing in this section, however, is intended to prevent either party from obtaining injunctive relief in court to prevent irreparable harm pending the conclusion of any such arbitration. Each party to an arbitration or litigation hereunder shall be responsible for the payment of its own attorneys’ fees.

Notice. Notices and all other communications contemplated by this Agreement shall be in writing and shall be deemed to have been duly given when personally delivered or when mailed by U.S. registered or certified mail, return receipt requested and postage prepaid or deposited with Federal Express Corporation, with shipping charges prepaid. In the case of the Executive, mailed notices shall be addressed to him or her at the home address which he or she most recently communicated to the Company in writing. In the case of the Company, mailed notices shall be addressed to its corporate headquarters, and all notices shall be directed to the attention of its Secretary.

Waiver. No provision of this Agreement shall be modified, waived or discharged unless the modification, waiver or discharge is agreed to in writing and signed by the Executive and by an authorized officer of the Company (other than the Executive). No waiver by either party of any breach of, or of compliance with, any condition or provision of this Agreement by the other party shall be considered a waiver of any other condition or provision or of the same condition or provision at another time.

Withholding Taxes. All payments made under this Agreement shall be subject to reduction to reflect taxes or other charges required to be withheld by law.

Severability. The invalidity or unenforceability of any provision or provisions of this Agreement shall not affect the validity or enforceability of any other provision hereof, which shall remain in full force and effect.

No Retention Rights. Nothing in this Agreement shall confer upon the Executive any right to continue in service for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Company or any subsidiary of the Company or of the Executive, which rights are hereby expressly reserved by each, to terminate his or her service at any time and for any reason, with or without Cause.

Choice of Law. The validity, interpretation, construction and performance of this Agreement shall be governed by the laws of the State of Texas (other than its choice-of-law provisions).