Document:

EX-4.21

 Exhibit 4.21 

EXECUTION VERSION` 
 CONSULTING

 AND 
 INTERIM
CHIEF FINANCIAL OFFCER AGREEMENT 
 This Consulting and Interim Chief Financial Officer Agreement (“Agreement”) is
effective as of the 14th day of May, 2020 by and among Mereo BioPharma Group plc, a company incorporated in England and Wales with a registered office at 1 Cavendish Place, London W1G 0QF (the “Company”), MSW Consulting Inc., a
corporation with headquarters located at 49 Beacon Street, Unit 3 Boston, MA 02108 (“Consultant”), and Michael Wyzga (”Wyzga” or “Executive”). 

WHEREAS, the Company desires to retain Consultant as an independent contractor to perform consulting services for the Company for a
period of time, and Consultant is willing to perform such services, on terms set forth more fully below. 
 WHEREAS, upon the
departure of the Company’s current chief financial officer, the Company wishes to appoint Executive as its interim chief financial officer (“Interim CFO”), on terms also set forth more fully below, for an expected period of less than
one year; and 
 WHEREAS, Executive desires to accept his appointment as Interim CFO; 

NOW THEREFORE, in consideration of the mutual promises contained herein, the parties agree as follows: 

Part I. Consulting Services 

1.    Consulting Period. The engagement of Consultant pursuant to this Agreement will commence on the date first written above, and
unless terminated earlier pursuant to Part I, Section 3 (Termination of Consulting Period) of this Agreement, will terminate upon Wyzga’s assuming the position of Interim CFO. The period during which Consultant is providing the
Services (as defined below) pursuant to this Agreement shall constitute the “Consulting Period.” 
 2.    Services
and Compensation. During the Consulting Period, Consultant agrees to perform for the Company the services requested by the Company, including the duties and tasks described in Exhibit A (collectively, “Services”).
Consultant agrees to devote such time to these Services as is reasonably necessary to perform them, which shall be at least as much time as is set forth on Exhibit A. 

Except as expressly stated herein, only Michael Wyzga, the authorized service provider (“Authorized Service Provider”), will
provide the Services on behalf of Consultant. Consultant acknowledges and agrees that the Company entered into this Agreement for the Consulting Period to retain the Consultant to perform the Services. Services are unique to the Company and the
Company has determined that Michael Wyzga is exceptionally qualified to perform them by virtue of his education, training and experience, and the Services are not to be performed by other individuals. 

 During the Consulting Period, with effect from the date notified in writing by the
Consultant to the Company, the Company agrees to pay Consultant the compensation set forth in Exhibit A as sole compensation for the performance of the Services. It is understood and agreed that Consultant will be an independent contractor.
Consultant will perform the Services under the Company’s general direction as to the result of activity but Consultant shall determine, in Consultant’s discretion, the time, manner and means by which the Services are accomplished, subject
to the express conditions that Consultant will at all times comply with applicable law. Wyzga need not perform the Services on the Company’s premises. It is also expressly understood that during the Consulting Period, neither Consultant nor the
Authorized Service Provider shall be considered an agent or employee of the Company, and shall have no authority whatsoever to bind the Company by contract or otherwise. Consultant, on behalf of itself and the Authorized Service Provider, expressly
waives any right to participate in any of the Company’s employee benefit plans or perquisites. Consultant, on behalf of itself and the Authorized Service Provider, further disclaims any intention or right to participate in any of the
Company’s employee benefit plans or perquisites even if Consultant’s or the Authorized Service Provider’s status with the Company is determined by a third party tribunal to be that of an employee. 

Consultant agrees that during the Consulting Period, Consultant will from time to time keep the Company advised as to Consultant’s
progress in performing the Services hereunder and that Consultant will, as requested by the Company, prepare written reports with respect thereto. It is understood that the time required in the preparation of such written reports shall be considered
time devoted to the performance of Consultant’s Services. 
 Consultant, on behalf of itself and the Authorized Service Provider,
acknowledges that Company may publicize Consultant’s and the Authorized Service Provider’s role with Company by including Consultant’s and the Authorized Service Provider’s name and publicly available information regarding
Consultant and/or the Authorized Service Provider in Company’s published materials (including but not limited to its website, presentations, and business plan materials). Consultant and the Authorized Service Provider understand that this
Agreement may be part of one or more federal securities filings. 
 3.    Termination of Consulting Period. Either Consultant or
the Company may terminate the Consulting Period upon giving thirty (30) days prior written notice thereof to the other party. The Consulting Period and this Agreement shall terminate immediately upon the Authorized Service Provider’s
death. The Company may, in addition to any other rights it may have at law or in equity, also terminate this Agreement immediately and without prior notice if Consultant or the Authorized Service Provider refuses to or is unable to perform the
Services, or is in breach of any material provision of this Agreement. Upon such termination all rights and duties of the parties with respect to the Consultant’s provision of Services and the Company’s compensation of the Consultant and
the Authorized Service Provider for such Services shall cease except that the Company shall be obligated to pay, within thirty (30) days of the effective date of termination, all amounts owing to Consultant pursuant to Exhibit A for Services
actually performed and reimbursable expenses actually incurred prior to termination, if any, in accordance with the provisions of Exhibit A. 

  
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 4.    Independent Contractor; Taxes; Indemnification. Nothing in this
Agreement shall in any way be construed to render Consultant or the Authorized Service Provider to be an agent, employee or representative of the Company. Consultant shall (and shall cause the Authorized Service Provider to) perform the Services
hereunder as an independent contractor. Consultant acknowledges and agrees that Consultant is obligated to report as income all compensation received by Consultant pursuant to this Agreement, and Consultant agrees to and acknowledges the obligation
to pay all taxes, including without limitation all federal and state income tax, social security taxes and unemployment, disability insurance and workers’ compensation applicable to Consultant and any person who performs Services in connection
with this Agreement, and that Consultant will not be eligible for any employee benefits (nor does Consultant desire any of them) and expressly waives any entitlement to such benefits. Consultant further agrees to indemnify the Company and hold it
harmless to the extent of any obligation imposed on the Company (i) to pay withholding taxes or similar items or (ii) resulting from Consultant’s being determined not to be an independent contractor. 

Except insofar as it would preclude the Consultant from providing the Services under this Agreement or violate Part III, Section 7
(Avoidance of Conflict of Interest) hereof, Consultant is free to perform services for any other person. Consultant, on behalf of itself and the Authorized Service Provider, further acknowledges and agrees to the following: 

(a)    While providing the Services pursuant to Part I of this Agreement, Consultant and the Authorized Service Provider
is, and shall at all times be and remain, an independent contractor; 
 (b)    Consultant is customarily engaged in an
independently established trade, occupation, profession or business of the same nature as that involved in providing Services; 

(c)    Nothing in this Agreement or otherwise shall be construed as identifying Consultant as an employee, agent or legal
representative of the Company or any of the Company’s related or affiliated entities during the Consulting Period for any purpose whatsoever; 

(d)    Consultant and the Authorized Service Provider are not authorized to transact business, incur obligations, sell
goods, receive payments, solicit orders or assign or create any obligation of any kind, express or implied, on behalf of the Company or any of the Company’s related or affiliated entities, or to bind in any way whatsoever, or to make any
promise, warranty or representation on behalf of the Company or any of the Company’s related or affiliated entities with respect to any matter, except as expressly authorized in writing by the Company; 

(e)    While Consultant will receive instruction on the objects and goals for which he or she is responsible, during the
Consulting Period, the Company has no right to control the manner in which Consultant performs Services under this Agreement and Consultant is free to perform Services in the manner Consultant deems fit and in accordance with recognized standards
for such services; 
 (f)    Consultant shall not (and shall not permit the Authorized Service Provider to) use the
Company’s trade names, trademarks, service names or service marks without the prior written approval of the Company; and 

  
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 (g)    If, at any time, Consultant’s or the Authorized Service
Provider’s status with the Company as an independent contractor changes or Consultant or the Authorized Service Provider is ever deemed, with respect to the Services performed during the Consulting Period, to be an employee of the Company, each
of the covenants set forth above and this Agreement remains in full force and effect in its entirety until and unless it is replaced with a subsequent and superseding agreement. 

5.    Limited Warranty. Consultant, on behalf of itself and the Authorized Service Provider, represents and warrants that all
services rendered hereunder during the Consulting Period will be performed in compliance with all applicable laws and regulations and in a professional manner in accordance with the highest industry standards and practices. Consultant, on behalf of
itself and the Authorized Service Provider, represents and warrants that Consultant and the Authorized Services Provider will perform Consultant’s and the Authorized Services Provider’s responsibilities under this Agreement in a manner
that does not infringe, or constitute an infringement or misappropriation of any patent, copyright or other proprietary right of any third party. Except as expressly stated in this Agreement, Consultant, on behalf of itself and the Authorized
Services Provider, disclaims all other express or implied warranties with respect to his or her performance of the Services. 
 II. Employment as Interim
Chief Financial Officer of the Company 
 1.    Employment Period. The employment of Wyzga as Interim CFO pursuant to this
Agreement will commence on the date on which his appointment as Interim CFO becomes effective and, unless terminated earlier pursuant to Part II, Section 8 hereof (Termination of Employment), will terminate on the date on which the employment
of his successor as the chief financial officer of the Company commences. The period during which Wyzga is employed by the Company as Interim CFO pursuant to this Agreement shall constitute the “Employment Period.” 

2.    Position, and Duties. During the Employment Period, Wyzga shall serve as chief financial officer of the Company and shall
have the normal duties and responsibilities which are consistent with Wyzga’s position as chief financial officer and as the board of directors of the Company (“Board”) may direct from time to time direct.. Wyzga shall report
to the chief executive officer of the Company. 
 3.    Best Efforts. During Wyzga’s employment, Wyzga shall:
(i) devote Wyzga’s full professional time and attention to the performance of Wyzga’s duties for the Company and its subsidiaries and related divisions and business lines; (ii) use Wyzga’s best efforts to dutifully,
faithfully and efficiently perform his duties hereunder, and obey all reasonable and lawful directions given by or under the authority of the Board; and (iii) refrain from engaging in any other business, profession or occupation for
compensation or otherwise which would conflict, directly or indirectly, with the rendition of services to the Company. Wyzga may engage in charitable, civic and community activities and manage Wyzga’s personal investments provided that such
activities do not materially interfere with the performance of his duties hereunder or conflict with the conditions of his employment, all in a manner consistent with his duties and responsibilities. 

  
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 4.    Adherence to Company Policies and Applicable Rules. During the Employment
Period, Wyzga shall: (i) comply with the Company’s articles of association, rules, and regulations; (ii) comply with the rules of any securities or investment exchange or regulatory or governmental body to which the Company is
subject from time to time (including the US Securities and Exchange Commission and Nasdaq); (iii) comply with, and procure compliance with, so far as he is able, that his spouse or civil partner and dependent children (if any) or any trust in which
he, his spouse, or civil partner or dependent children may be concerned or interested in as trustee or beneficiary, any code of conduct relating to securities transactions by directors and specified employees applicable in the Company and its
subsidiaries; (v) exercise his duties in compliance with the requirements of the United Kingdom’s Bribery Act 2010; and (v) comply with such office policies, procedures, and practices as may be established from time to
time through office manuals, policy statements, memoranda, or other communications to the Company’s officers, directors, and employees. Wyzga understands that these policies, procedures, and practices are subject to change, do not constitute
contractual rights or obligations, and that no employee has any right to the continuance of any given policy or practice unless specifically set forth herein. 

5.    During the Employment Period, Executive’s primary work location shall be in Boston, Massachusetts; provided, however, that
(i) Wyzga may elect to perform his duties from other locations from time to time; and (ii) Wyzga shall travel to other locations and countries as and when required by the Board including, but not limited to, travel to the Company’s offices
in the United Kingdom. 
 6.    Compensation. During the Employment Period, the Company agrees to pay Wyzga the compensation set
forth in Exhibit B as sole compensation for the performance of his duties as Interim CFO. In addition, during the Employment Period, Wyzga shall be eligible to be granted Company stock options on the same basis as other senior executives of
the Company. 
 7.    Business Expenses. During the Employment Period, the Company shall reimburse Wyzga for all reasonable
expenses incurred by Wyzga in the course of performing Wyzga’s duties under this Agreement that are consistent with the Company’s policies in effect from time to time with respect to travel, entertainment and other business expenses,
subject to the Company’s requirements applicable generally with respect to reporting and documentation of such expenses. 

8.    Termination of Employment. Wyzga’s employment with the Company is at-will and
not for any specified period. Either the Company or Wyzga may terminate the Employment Period and this Agreement upon giving thirty (30) days prior written notice thereof to the other party. The Employment Period and this Agreement shall
terminate immediately upon Wyzga’s death. The Company may, in addition to any other rights it may have at law or in equity, also terminate this Agreement immediately and without prior notice if Wyzga refuses to or is unable to perform his
duties as Interim CFO, has committed an act of material misconduct or gross negligence, or is in breach of any material provision of this Agreement. Upon such termination, the Company’s compensation obligations to Wyzga shall cease except that
the Company shall be obligated to pay, within thirty (30) days of the effective date of termination (or such earlier time as may be required by law), (i) the compensation earned and owing to Wyzga pursuant to Exhibit B for the period through
and including the date on which his employment terminates, and (ii) reimbursable expenses actually incurred by Wyzga prior to termination. If, on the date of termination, Wyzga 

  
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holds any other office or position with the Company or its subsidiaries (other than that of being a member of the Board, which unless he has resigned or has been removed, Wyzga shall continue to
hold following the end of the Employment Period) (“Other Offices and Positions”), Wyzga shall be deemed to have resigned from all Other Offices and Positions as of his employment termination date. Wyzga hereby covenants that upon
and following the date of termination, he will take such actions and execute such instruments as the Company determines to be necessary or advisable in order to effect such resignations. 

9.    Executive’s Cooperation. During the Employment Period and thereafter, Wyzga shall reasonably cooperate with the Company
and its affiliates or subsidiaries in any internal investigation or administrative, regulatory or judicial proceeding as reasonably requested by the Company (including, without limitation, Wyzga’s being reasonably available to the Company upon
reasonable notice for interviews and factual investigations, appearing at the Company’s reasonable request to give testimony without requiring service of a subpoena or other legal process, volunteering to the Company all pertinent information
and turning over to the Company all relevant documents which are or may come into Wyzga’s possession, all at times and on schedules that are reasonably consistent with Wyzga’s other permitted activities and commitments) at reasonable
times. In the event the Company requires Wyzga’s cooperation in accordance with this section, the Company shall reimburse Wyzga solely for reasonable travel expenses (including lodging and meals, upon submission of receipts). Nothing about the
foregoing shall preclude Wyzga from testifying truthfully in any forum or from providing truthful information to any government agency or commission. 

Part III 
 In this Part III, “Wyzga” shall refer
to Consultant, Michael Wyzga in his capacity as authorized service provider, and Michael Wyzga in his capacity as Interim CFO, and the promises, duties, and obligations imposed on “Wyzga” under this Part III (i) are each made by Consultant
and by Michael Wyzga in his capacity as Interim CFO, and (ii) Consultant will cause Michael Wyzga, in his capacity as authorized service provider, to perform or refrain from, as applicable, each of the promises, duties and obligations imposed
on Consultant by this Part III. 
 1.    Confidentiality. “Confidential Information” means all trade secrets and
confidential or proprietary information, whether or not in writing, concerning the Company’s business, technology, business relationships or financial affairs which the Company has not released to the general public. By way of illustration,
Confidential Information may include, but is not limited to, information or material which has not been made generally available to the public, such as: (a) corporate information, including plans, strategies, methods, policies,
resolutions, negotiations or litigation; (b) marketing information, including strategies, methods, customer identities or other information about customers, prospect identities or other information about prospects, or market analyses or
projections; (c) financial information, including cost and performance data, debt arrangements, equity structure, investors and holdings; and (d) operational and technological information, all proprietary data , plans,
specifications, manuals, forms, templates, software, designs, methods, procedures, formulas, discoveries, inventions, improvements, concepts and ideas; and (e) personnel information, including personnel lists, reporting or
organizational structure, resumes, personnel data, compensation structure, performance evaluations and termination arrangements or documents. Confidential Information also includes information received in confidence by the Company from its customers
or suppliers or other third parties. 

  
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 2.    Recognition of Company Rights. Wyzga will not, at any time, without the
Company’s prior written permission, either during or after the term of this Agreement, disclose any Confidential Information to anyone outside of the Company, or use or permit to be used any Confidential Information for any purpose other than
(i) the performance of the Services during the Consulting Period, and (ii) Wyzga’s performance of his duties and responsibilities as Interim CFO during the Employment Period, for or on behalf of the Company. Wyzga will
cooperate with the Company and use best efforts to prevent the unauthorized disclosure or use of any and all Confidential Information. Wyzga will deliver to the Company all copies of Confidential Information in Wyzga’s possession or control
upon the earlier of a request by the Company or termination of this Agreement for any reason. 
 3.    Rights of Others. Wyzga
understands that the Company is now and may hereafter be subject to non-disclosure or confidentiality agreements with third persons which require the Company to protect or refrain from use of Confidential
Information. Wyzga, agrees to be bound by the terms of such agreements in the event Wyzga has access to such Confidential Information. 

4.    Prior Agreements. Wyzga agrees that Wyzga will not, during the term of this Agreement, improperly use or disclose any
proprietary information or trade secrets of any former or current employer or other person or entity with which Wyzga has an agreement or duty to keep in confidence information acquired by Wyzga, if any, and that Wyzga will not bring onto the
premises of the Company any unpublished document or proprietary information belonging to such employer, person or entity unless consented to in writing by such employer, person on entity. 

5.    Ownership. Wyzga will make full and prompt disclosure to the Company of all inventions, discoveries, designs, developments,
methods, modifications, improvements, ideas, products, processes, databases, computer programs, formulae, techniques, know-how, trade secrets, graphics or images, and audio or visual works and other works of authorship (collectively
“Developments”), whether or not patentable or copyrightable, that are created, made, conceived or reduced to practice by Wyzga (alone or jointly with others) or under Wyzga’s direction during the term of this Agreement. Wyzga
acknowledges that all work performed by Wyzga is on a “work for hire” basis, and Wyzga hereby assigns and transfers and, to the extent any such assignment cannot be made at present, will assign and transfer, to the Company and its
successors and assigns all Wyzga’s right, title and interest in all Developments that (i) relate to the business of the Company or any customer of the Company or any of the products or services being researched, developed, manufactured,
performed or sold by the Company or which may be used with such products or services; or (ii) result from tasks assigned to Wyzga by the Company and/or the Services and/or Wyzga’s employment; or (iii) result from the use of
premises or personal property (whether tangible or intangible) owned, leased or contracted for by the Company (“Company-Related Developments”), and all related patents, patent applications, trademarks and trademark applications,
service marks and service mark applications, copyrights and copyright applications, and other intellectual property rights in all countries and territories worldwide and under any international conventions (“Intellectual Property
Rights”). Wyzga shall, at the request of Company execute all documents as are 

  
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required to vest ownership of any Company-Related Developments and Intellectual Property Rights in Company and will assist Company in obtaining and enforcing patent, copyright and other forms of
legal protection for the Company-Related Developments in any country. Wyzga irrevocably appoints Company as Wyzga’s attorney-in-fact to execute all such documents
as may be required by Company to so vest such ownership of such Inventions in Company. Wyzga shall treat all Inventions as Confidential and Proprietary Information of Company. 

This Agreement does not obligate Wyzga or require Wyzga to assign to the Company any Development which, in the sole judgment of the Company,
reasonably exercised, is developed entirely on Wyzga’s own time and does not relate to the business efforts or research and development efforts in which, during the term of this Agreement, the Company actually is engaged or reasonably would be
engaged, and does not result from the use of premises or equipment owned or leased by the Company. However, Wyzga will also promptly disclose to the Company any such Developments for the purpose of determining whether they qualify for such
exclusion. Wyzga, understands that to the extent this Agreement is required to be construed in accordance with the laws of any state which precludes a requirement in an agreement to assign certain classes of inventions made by a Wyzga, this Part
III, Section 5 (Ownership) will be interpreted not to apply to any invention which a court rules and/or the Company agrees falls within such classes. Wyzga also hereby waives all claims to any moral rights or other special rights which Wyzga
may have or accrue in any Company-Related Developments. 
 6.    Records; Reports. Wyzga will keep and maintain adequate and
current records of all Confidential Information and Company-Related Developments developed by Wyzga during the term of this Agreement, which records will be available to and remain the sole property of the Company at all times. All Developments,
files, letters, notes, memoranda, reports, records, data, sketches, drawings, notebooks, layouts, charts, quotations and proposals or other written, photographic or other tangible material containing Confidential Information, whether created by
Wyzga or others, which come into Wyzga’s custody or possession, are the exclusive property of the Company to be used by Wyzga only in the performance of the Services and Wyzga’s employment duties. Any property situated on the
Company’s premises and owned by the Company, including without limitation computers, disks and other storage media, filing cabinets or other work areas, is subject to inspection by the Company at any time with or without notice. In the event of
the termination of this Agreement for any reason, Wyzga will promptly deliver to the Company all files, letters, notes, memoranda, reports, records, data, sketches, drawings, notebooks, layouts, charts, quotations and proposals, specification
sheets, or other written, photographic or other tangible material containing Confidential Information, and other materials of any nature pertaining to the Confidential Information of the Company and to the Services and Wyzga’s employment by the
Company, and will not take or keep in Wyzga’s possession any of the foregoing or any copies. 
 7.    Avoidance of Conflicts of
Interest. Wyzga represents and warrants that Wyzga has no outstanding agreement or obligation that is in conflict with any of the provisions of this Agreement, or that would preclude Wyzga from fully complying with the provisions hereof, and
further certifies that Wyzga will not enter into such conflicting agreement during the term of this Agreement. Wyzga will advise the Company at such time as any activity of either the Company or another business presents Wyzga with a conflict of
interest or the appearance of a conflict of interest. Wyzga will take whatever action is requested by the Company to resolve any conflict or 

  
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appearance of conflict which it finds to exist. Wyzga further represents and warrants that Wyzga has full power and authority to enter into this Agreement and perform his or her obligations
hereunder. 
 8.    Indemnification. Wyzga shall indemnify and hold the Company, its affiliates and their respective directors,
officers, agents and employees harmless from and against all claims, demands, losses, damages and judgments, including court costs and attorneys’ fees, arising out of or based upon (i) any claim that the Services provided hereunder or, any
related Intellectual Property Rights or the exercise of any rights in or to any Company-Related Development or related Intellectual Property Rights infringe on, constitute a misappropriation of the subject matter of, or otherwise violate any patent,
copyright, trade secret, trademark or other proprietary right of any person or breaches any person’s contractual rights; and (ii) any breach or alleged breach by Wyzga or the Authorized Services Provider of any representation,
warranty, certification, covenant, obligation or other agreement set forth in this Agreement. 
 9.    Limitation of Liability.
Except for liability arising from Wyzga’s or the Authorized Service Provider’s breach of Sections 2 (Recognition of Company Rights), 3 (Rights of Others), 5 (Ownership) of this Part III, or Wyzga’s indemnification obligations
hereunder, Wyzga shall not be liable to the Company for special, indirect, reliance, incidental, or consequential damages. Wyzga’s liability arising out of or in connection with this Agreement during the Consulting Period shall not exceed the
fees paid to Wyzga under this Agreement. The Company’s liability arising out of or in connection with this Agreement during the Consulting Period shall not exceed the fees paid to Wyzga under this Agreement. The Company shall not be liable to
the Wyzga for special, indirect, reliance, incidental, or consequential damages. 
 10.    Term. The term of this Agreement will
commence on the date first written above, and will continue until the earlier of (i) the termination of the Consulting Period unless the Employment Period commences immediately following the end of the Consulting Period, or (ii) the
termination of the Employment Period (the “Term”). The termination of the Term shall not affect the continuation of obligations that do not expressly cease pursuant to this Agreement. 

11.    Assignment. Neither this Agreement nor any right hereunder or interest herein may be assigned or transferred by Wyzga
without the express written consent of the Company. The Company may assign any or all of its rights and obligations under this Agreement without Wyzga’s written consent to any affiliate or to another third party affiliate by way of merger,
acquisition, consolidation, or sale or transfer of all or substantially all of the Company’s assets or capital stock. Wyzga expressly consents to be bound to the provisions of this Agreement for the benefit of the Company or any parent,
subsidiary or affiliate without the necessity that this Agreement be re-executed. Any attempted assignment, delegation or transfer by a third party hereto in violation hereof shall be null and void. Subject to
the foregoing, this Agreement shall be binding on the parties and their successors and assigns. 
 12.    Equitable Relief. Wyzga
and the Company agree that it would be impossible or inadequate to measure and calculate the Company’s damages from any breach by Wyzga of any part(s) of Sections 2 (Recognition of Company Rights), 5 (Ownership), 6 (Records; Reports), or 7
(Avoidance of Conflicts of Interest) of this Part III (the “Specified Sections”). Accordingly, Wyzga and the Company agree that if Wyzga breaches this Agreement, the Company will have

  
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available, in addition to any other right or remedy available, the right to obtain from any court of competent jurisdiction an injunction restraining such breach or threatened breach and specific
performance of the Specified Sections. Wyzga and the Company further agree that no bond or other security shall be required in obtaining such equitable relief and Wyzga and the Company, hereby consent to the issuances of such injunction and to the
ordering of such specific performance. 
 13.    Notices. Notices. Any notice provided for in this Agreement shall be in writing
and shall be either personally delivered, sent by reputable overnight courier service or mailed by first class mail, return receipt requested, to the recipient at the address below indicated: 

Notice to Consultant and Michael Wyzga: 

To Michael Wyzga at such address as most currently appears in the records of the Company 

Email: [    ] 

Notices to the Company: 

Mereo BioPharma Group plc 
 One
Cavendish Place 
 London W1G 0QF 

United Kingdom 
 Attention: The
General Counsel 
 Email: [    ] 

With a copy to: 
 Charles
Sermon 
 General Counsel 

Mereo Biopharma Group plc 
 1
Cavendish Place 
 London W1G 0QF 

United Kingdom 
 Email:
[    ] 
 or such other address or to the attention of such other person as the recipient party shall have specified by prior written
notice to the sending party. Notice shall be sufficient in all respects if given and delivered in person, by electronic mail, by facsimile, by overnight courier, or by mail, postage prepaid, to the receiving party at such party’s address. Such
notice shall be deemed to have been given as of one (1) day following the date deposited with a recognized overnight courier service, three (3) days following the date deposited in the mail to an address in the same country, seven
(7) days following the date deposited in the mail to an address in another country, and immediately following the notice being sent if sent by electronic mail or by facsimile. 

14.    Severability. If any provision in this Agreement shall be found or be held to be invalid or unenforceable in any
jurisdiction in which this Agreement is being performed, then the meaning of said provision shall be construed, to the extent feasible, so as to render the provision 

  
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enforceable, and if no feasible interpretation would save such provision, it shall be severed from the remainder of this Agreement which shall remain in full force and effect. In such event, the
parties shall negotiate, in good faith, a substitute, valid and enforceable provision which most nearly effects the parties’ intent in entering into this Agreement. 

15.    Amendment. This Agreement (including Exhibits A and B) may not be amended in any respect except by a writing signed by the
parties. 
 16.    Effect on Directors Appointment Letter. This Agreement shall have no effect on Wyzga’s status as a member
of the Board, except that during the Employment Period, 
 (a)    Wyzga shall be an executive member of
the Board; 
 (b)    Wyzga shall receive compensation from the Company solely in his capacity as Interim
CFO pursuant to Exhibit B, serving as a member of the Board for no additional consideration; and 

(c)    Wyzga’s letter of appointment to the Board (the “Appointment Letter”) shall be
amended in accordance with the terms set out in Exhibit C. 
 In addition, in order to comply with current Nasdaq rules, while serving as Interim CFO and
for a period of three years thereafter, Wyzga shall not serve as a member of the Board’s Audit and Risk Committee. To the extent necessary to effect the forgoing provisions of this Part III, Section 16, this Part III,
Section 16 shall be constitute an amendment to the Appointment Letter and to the relevant Company option grant agreements. 

17.    Entire Agreement. The terms and conditions herein contained constitute the entire agreement between the parties and
supersede all previous agreements and understandings, whether oral or written, between the parties hereto with respect to the subject matter hereof, and no agreement or understanding varying or extending the same shall be binding upon either party
hereto unless in a written document which expressly refers to this Agreement and which is signed by the party to be bound thereby. For the avoidance of doubt, Wyzga’s Appointment Letter, as modified by Part III, Section 16 (Effect on
Directors Appointment Letter) remains in effect. 
 18.    Governing Law and Personal Jurisdiction. This Agreement and any action
related thereto will be governed, controlled, interpreted, and defined by and under the laws of the State of New York, without giving effect to any conflicts of laws principles that require the application of the law of a different state. Any
disputes under this Agreement may be brought in the state courts and the Federal courts located in the Borough of Manhattan of the City of New York in the State of New York, and each of the parties and the Authorized Service Provider hereby consent
to the personal jurisdiction and exclusive venue of these courts. 
 19.    Costs. Each party hereby agrees that if it is held by
any court of competent jurisdiction to be in violation, breach, or nonperformance of any of the terms of this Agreement, then the prevailing party will pay all reasonable costs of such action or suit, including reasonable attorney’s fees. 

  
 11 

 20.    No Waiver. No waiver of any term or condition of this Agreement shall be
valid or binding on either party unless the same shall be been mutually assented to in writing by the parties to the waiver. The failure of a party to enforce at any time any of the provisions of this Agreement, or the failure to require at any time
performance by the another party of any of the provisions of this Agreement, shall in no way be construed to be a present or future waiver of such provisions, nor in any way affect the right of any party to enforce each and every such provision
thereafter. The express waiver by a party of any provision, condition or requirement of this Agreement shall not constitute a waiver of any future obligation to comply with such provision, condition or requirement. 

21.    Defend Trade Secrets Act of 2016. Wyzga acknowledges receipt of the following notice under 18 U.S.C §
1833(b)(1): “An individual shall not be held criminally or civilly liable under any Federal or State trade secret law for the disclosure of a trade secret that (A) is made (i) in confidence to a Federal, State, or local
government official, either directly or indirectly, or to an attorney; and (ii) solely for the purpose of reporting or investigating a suspected violation of law; or (B) is made in a complaint or other document filed in a
lawsuit or other proceeding, if such filing is made under seal.” 
 22.    Counterparts. This Agreement may be signed in one
or more counterparts. 
 23.    Taxes. The Company may withhold, or cause to be withheld, from any amounts payable under this
Agreement all federal, state, city or other taxes as the Company or any of its Affiliates, is required to withhold pursuant to any applicable law, regulation or ruling. Notwithstanding any other provision of this Agreement, the Company shall not be
obligated to guarantee any particular tax result to any party with respect to any amount paid by the Company to such other party as fees or compensation. Each of the Consultant, the Authorized Service Provider, and Wyzga shall be responsible for any
taxes imposed on any amount received by them from the Company as a payment of fees or compensation. 
 24.    Personal
Information. Wyzga acknowledges and agrees that the Company is permitted to hold personal information about him as part of its personnel and other business records and, in accordance with applicable law, may use such information in the course of
the Company’s business. 
 25.    Advice of Counsel. Each party represents and warrants that it has had a full opportunity
to seek advice and representation by independent counsel of its own choosing in connection with this Agreement and it has either received such advice or, in its business judgment, decided not to seek such advice. 

26.    Section Headings; Interpretation. The section headings in this Agreement are for convenience of reference only, and they
form no part of this Agreement and shall not affect its interpretation. It is the parties’ intention that this Agreement not be construed more strictly with regard to Wyzga or the Company. 

27.    409A Compliance. The intent of the parties is that payments and benefits under this Agreement comply with
Section 409A and, accordingly, to the maximum extent permitted, this Agreement shall be interpreted to be in compliance therewith. In no event shall the Company or its subsidiaries or affiliates be liable for any additional tax, interest
or penalty that may be imposed on a party under Section 409A or damages for failing to comply with Section 409A. 

  
 12 

 (a)    Notwithstanding anything herein to the contrary, to the extent
required by Section 409A, upon a termination of Executive’s employment (other than as a result of death), if Executive is at the time a “specified employee” (within the meaning of Section 409A), distributions under this
Agreement determined, in whole or in part, to constitute “nonqualified deferred compensation” within the meaning of Section 409A and payable to Executive on account of Executive’s termination of employment or other
“separation from service” (within the meaning of Section 409A(a)(2)(A)(i) of the Code and the Treasury regulations issued thereunder) will be delayed until six months after such termination of employment, and such distributions will
be made at the beginning of the seventh month following the date of such termination of employment or other separation from service. A termination of employment shall not be deemed to have occurred for purposes of any provision of this Agreement
providing for the payment of any amounts or benefits upon or following a termination of employment unless such termination is also a “separation from service” within the meaning of Section 409A and, for purposes of any such provision
of this Agreement, references to a “termination,” “termination of employment” or like terms shall mean “separation from service.” 

(b)    To the extent that reimbursements or other in-kind benefits under this
Agreement or any amounts otherwise due to a party from the Company constitute “nonqualified deferred compensation” for purposes of Section 409A: (i) all such expenses or other reimbursements hereunder shall be made on or
prior to the last day of the taxable year following the taxable year in which such expenses were incurred by the party; (ii) any such right to reimbursement or in-kind benefits shall not be subject to
liquidation or exchange for another benefit; and (iii) no such reimbursement, expenses eligible for reimbursement, or in-kind benefits provided in any taxable year shall in any way affect the expenses
eligible for reimbursement, or in-kind benefits to be provided, in any other taxable year. 

(c)    For purposes of Section 409A, a right to receive any installment payments pursuant to this Agreement shall be
treated as a right to receive a series of separate and distinct payments. 
 (d)    Notwithstanding any other provision
of this Agreement to the contrary, in no event shall any payment under this Agreement that constitutes “nonqualified deferred compensation” for purposes of Section 409A be subject to offset by any other amount unless otherwise
permitted by Section 409A. 
 [Remainder of Page Intentionally Left Blank] 

  
 13 

 IN WITNESS WHEREOF, the parties hereto have caused to be executed or executed this
Consulting Agreement as of the day and year first above written. 
  

			
	MEREO BIOPHARMA GROUP PLC
		
	By:	 	 /s/ Denise Scots-Knight

	Name:	 	Denise Scots-Knight
	Title:	 	Chief Executive Officer
	
	MSW CONSULTING INC.
		
	By:	 	 /s/ Michael S Wyzga

	Name:	 	Michael S Wyzga
	Title:	 	President, MSW Consulting Inc.
	
	MICHAEL WYZGA (In his individual capacity as and as Authorized Service Provider)
	
	  

  
 14 

 EXHIBIT A 

CONSULTING SERVICES AND COMPENSATION 

  
 15 

 EXHIBIT B 

INTERIM CFO COMPENSATION 

  
 16 

 EXHIBIT C 

DIRECTOR’S APPOINTMENT LETTER 

  
 17EX-4.26

 Exhibit 4.26 

Michael S Wyzga 
 [—] 

[—] 
 [—] 

[—] 
 14 May 2020 

Dear Mike 
 Letter of appointment between (1) Mereo BioPharma
Group plc (the “Company”) and (2) Mike Wyzga (“you”) dated 23 April 2019 (the “Appointment Letter”) 
 We refer to the
Appointment Letter and to the consulting and interim chief financial officer agreement between (1) the Company, (2) MSW Consulting Inc. (the “Consultant”) and (3) you to be entered into on or about the date of this letter (the
“Consulting/Interim CFO Agreement”). 
 Pursuant to the Consulting/Interim CFO Agreement, the Company will retain the Consultant as an
independent contractor to perform consulting services during the Consulting Period (as defined in the Consulting/Interim CFO Agreement). As the Authorized Service Provider (as defined in the Consulting/Interim CFO Agreement) under the
Consulting/Interim CFO Agreement, you will provide those consulting services on behalf of the Consultant. Upon your appointment as the Company’s interim chief financial officer on the terms of the Consulting/Interim CFO Agreement for the
Employment Period (as defined in the Consulting/Interim CFO Agreement), the Consulting Period will end. 
 In consideration for each of us entering into the
Consulting/Interim CFO Agreement, it is agreed that the Appointment Letter shall be amended as follows: 
  

	1.	 During the Consulting Period and the Employment Period, you shall continue as a director of the Company and the
Appointment Letter shall continue in full force and effect except to the extent provided otherwise in this letter. Your responsibilities under the Consulting/Interim CFO Agreement are incremental, and without prejudice, to your responsibilities
under the Appointment Letter (as amended by this letter). 

  

	2.	 Immediately following the Consulting Period (unless the Employment Period commences immediately following the
end of the Consulting Period) or the Employment Period, and unless the Appointment Letter is terminated pursuant to paragraph 9 below, the Appointment Letter shall be reinstated on the terms applicable immediately prior to this letter and the
Consulting/Interim CFO Agreement. 

  

	3.	 During the Employment Period, the annual fees payable to you pursuant to paragraph 1.1 of the Appointment
Letter shall not accrue or be payable. 

  

	4.	 Notwithstanding the references to “non-executive director” in any of paragraphs 2.1 to 2.11 of the
Appointment Letter, all of those paragraphs will continue to apply to you as a director during the Consulting Period and the Employment Period except to the extent provided otherwise in this letter. 

 

	5.	 Without prejudice to paragraph 4 of this letter, during the Employment Period, paragraphs 2.6(a) and (b) of the
Appointment Letter shall be varied so as to continue to apply to you to the extent that executive directors are also charged with the responsibilities contemplated by those paragraphs in relation to management (but not in relation to your own role
as a member of management and you shall recuse yourself from any evaluation by the directors of your performance). 

  

	6.	 Without prejudice to paragraph 4 of this letter, during the Employment Period, paragraph 2.6(c) of the
Appointment Letter shall be varied so as to continue to apply to you but it is acknowledged that as Interim CFO, your duties will include ensuring the integrity of the Company’s financial controls and ensuring that the Company’s systems of
risk management are robust and defensible; 

  

	7.	 Without prejudice to paragraph 4 of this letter, during the Employment Period, paragraph 2.6(d) of the
Appointment Letter shall not form part of your responsibilities but shall continue to fall within the terms of reference of the remuneration committee. 

  

	8.	 During the Employment Period, paragraph 2.11 of the Appointment Letter shall not apply. 

 

	9.	 If the Consulting/Interim CFO Agreement is terminated: 

 

	 	(a)	 pursuant to the second or third sentence of Part I, Section 3 of the Consulting/Interim CFO Agreement; or

  

	 	(b)	 pursuant to the third or fourth sentence of Part II, Section 8 of the Consulting/Interim CFO Agreement; or

  

	 	(c)	 otherwise by reason of any material or repeated breach of any obligations applying to you and whether under the
Appointment Letter (as amended by this letter) or the Consulting/Interim CFO Agreement, the Appointment Letter shall automatically terminate simultaneously without any requirement to provide separate notice. 

 

	10.	 During the Employment Period, any duty or responsibility of a director described in the Appointment Letter that
must only be performed by a non-executive director shall not apply to you but, save where there is a legal or regulatory or governance reason precluding such a duty or responsibility by an executive director, then any duty or responsibility of a
director described in the Appointment Letter will continue to apply unless expressly stated otherwise above. 

 This letter is governed
by, and shall be construed in accordance with, English law. Please countersign and return to us the attached copy of this letter to signify your acceptance of its terms. 

Yours sincerely 
  

			
	MEREO BIOPHARMA GROUP PLC
		
	By:	 	 /s/ Denise Scots-Knight

 Agreed and accepted: 
  

			
	MEREO BIOPHARMA GROUP PLC
		
	By:	 	 /s/ Michael S Wyzga

		
	Date:

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