Exhibit 10.1

July 26, 2019
Dear Mark:
It is my pleasure to offer you the position of General Counsel & Secretary at
Sesen Bio (the “Company" or "Sesen Bio"). Your start date will be August 1, 2019
(the “Commencement Date”). This letter summarizes important details about your
employment, should you accept this offer (“Letter Agreement”). This Letter
Agreement shall be effective on August 1, 2019, which shall also be your start
date (“Effective Date”).
1.    Title, Position and Duties: You will hold the position of General Counsel
& Secretary with the Company and you will report to the Chief Executive Officer
(“CEO”). You will have such duties and responsibilities as are usually performed
by the general counsel and secretary of a Delaware corporation, including such
duties as are reasonably and appropriately delegated to you from time to time by
the CEO or the Board of Directors (the “Board”), consistent with your position
as General Counsel & Secretary, and you will have the authority and resources
consistent with such position, subject to adjustments in resources consistent
with normal operating decisions of the CEO or the Board in the event of changes
in strategy or programs or any other changes to resources that are reasonable in
light of the Company’s then current financial condition.
2.    Full-Time and Best Efforts: As the Company’s General Counsel & Secretary,
which is a full-time position, we expect that you will devote substantially all
of your working time to the performance of your Company duties in a satisfactory
manner and to the best of your abilities at all times. You shall not engage in
any other business or occupation during your employment here, including, without
limitation, any activity that conflicts with the interests of the Company,
interferes with the proper and efficient performance of your duties for the
Company, or interferes with your exercise of judgment in the Company’s best
interests. Approval of the CEO and/or Board will be required for you to serve on
other outside boards while you are employed by the Company, including any
outside for-profit boards, which approval shall not be unreasonably withheld,
delayed or conditioned. Notwithstanding the foregoing, you will be permitted to
serve as an officer, director or trustee of any charitable, educational or
non-profit organization, without the Company’s prior consent, provided that such
services do not interfere with the performance of your duties to the Company or
represent an actual or apparent conflict of interest with your role at the
Company.
3.    Compensation: You shall receive an annualized salary of $350,000 (“Base
Salary”), pro-rated for the calendar year 2019, and paid in accordance with the
Company's standard payroll practices, and subject to all applicable tax
reporting and withholding. In January 2020, you will be considered for a merit
review in conjunction with your performance review (which generally is conducted
annually) and consistent with the Company’s compensation practices, as
determined by the Board in its sole discretion.
4.    Annual Bonus: You will be eligible for an annual target bonus of up to 35%
of your Base Salary, based upon achievement of both corporate and individual
goals, as determined by the Board or a designed committee of the Board (“Annual
Bonus”), and shall be subject to all applicable tax reporting and withholding.
The determination of whether an Annual Bonus will be granted, and the amount of
any such bonus, will be solely determined by the Board or a designated committee
of the Board in its sole discretion based on factors upon which the Board alone
may choose to rely. All Annual Bonuses, if any, will be payable no later than
March 15 of the year following the year in which they were earned. Bonuses are
prorated for percentage of year as a full time employee. Please note that you
must be employed on the date Annual Bonuses, if any, are paid, in order to be
eligible for and to earn such a payment, as such bonuses also serve as retention
incentives. The fact that you may receive a bonus in one year does not mean you
will receive one in any other year.
5.    Stock Option: Subject to and upon approval by the Board or a designated
committee of the Board, you will be granted, on your Commencement Date, an
option to purchase 200,000 shares of Common Stock, $0.001 par value per share,
of the Company (the “Common Stock”), under the Company’s 2014 Stock Incentive
Plan. The option grant (the “Grant”) shall have an exercise price equal to the
closing price of the Common Stock on the Nasdaq Global Market on the
Commencement Date and shall vest as to 6.25% of the shares subject to the Grant
at the end of each successive three-month period following the Grant Date until
the fourth anniversary of the Grant Date. The Board or a designated committee of
the Board will consider annually whether to grant additional equity awards to
its employees and you will be eligible to be considered for such additional
annual equity grants.
6.    Employee Benefits: The Company presently offers a comprehensive benefit
package that includes group health, dental and vision plans as well as life and
disability and time-off benefits. Benefits offered by the Company may change
from time to time in the sole discretion of the Board.
7.    Vacation Time: As a full-time employee of the Company, you are eligible
for up to fifteen (15) paid vacation days annually that are accrued on a monthly
basis at a rate of 1.25 days (10 hours) per month of full time employment. The
use and

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accrual of vacation is governed by the Company’s vacation pay policy in effect,
which may change from time to time in the sole discretion of the Board.
8.    Term of Employment; Restrictive Covenant Agreement: It is important for
you to understand that you are an employee “at will”. This means that you have
the right to terminate your employment relationship with Sesen Bio at any time
with or without notice, for any reason or no reason. Similarly, the Company has
the right to terminate its employment relationship with you, with or without
notice, at any time for any or no reason. As a condition of your employment with
the Company, you will be required to execute the enclosed Employee
Non-Competition, Non-Solicitation, Confidentiality, and Assignment Agreement.
Your employment and this Letter Agreement will be governed by the laws of the
Massachusetts.
9.    Severance Benefits: Notwithstanding the foregoing, in the event that Sesen
Bio terminates your employment without “Cause” or you resign with “Good Reason”
(each term as defined below and in either case a “Qualifying Termination”), you
will be eligible for the benefits outlined in sub-paragraphs A or B below (the
“Severance Benefits”), subject to the terms set forth in this Letter Agreement:
A.
If a Qualifying Termination occurs: (i) Sesen Bio will pay you severance in the
form of continuation of your Base Salary for a total of 12 months (“Severance
Period”), such amount to be paid in accordance with the Company’s then current
payroll practices, except as otherwise specified in this Letter Agreement,
beginning on the Company’s first regular payroll date that occurs after the
Payment Date (as defined below), and (ii) subject to the terms and conditions
provided for in COBRA, and subject to your timely election of COBRA and
copayment of premium amounts at the active employee’s rate, the Company shall
pay its then current share of premium payments for group health and dental
insurance after the termination date through the earliest of (1) your Severance
Period as outlined above, (2) the date you become employed with benefits
substantially comparable to the benefits provided under the corresponding
Company plan, and (3) the date you become ineligible for COBRA benefits;
provided, however, that such Company-paid premiums may be recorded as additional
income pursuant to Section 6041 of the Internal Revenue Code of 1986, as amended
(the “Code”) and not entitled to any tax qualified treatment to the extent
necessary to comply with or avoid the discriminatory treatment prohibited by the
Patient Protection and Affordable Care Act of 2010 and the Health Care and
Education Reconciliation Act of 2010 or Section 105(h) of the Code. You shall be
responsible for the entire COBRA premium should you elect to maintain this
coverage after the earliest of the dates specified in Sections 9.A.(ii)(1)-(3)
above.

B.
If a Qualifying Termination occurs within twelve (12) months after a Change in
Control Transaction (as defined below), then: (i) you will be eligible for the
same severance payments and COBRA premium assistance as set forth in sections
9.A.i-A.ii above, subject to the same terms, conditions, and limitations as
described therein; and (ii) the vesting of 100% of your then outstanding
unvested equity grants shall be accelerated, such that all unvested equity
grants vest and become fully exercisable or non-forfeitable as of the
termination date for a period of 90 days following the termination date; after
such 90-day period, all unvested equity grants will no longer be exercisable.

For the sake of clarity, it shall not be a “Qualifying Termination” if you
voluntarily resign without Good Reason, your employment terminates For Cause or
your employment terminates because of your death or due to your suffering a
Disability (as defined below).
C.
The Severance Benefits will be subject to the following terms:

i.
Solely for purposes of Section 409A of the Code, each salary continuation
payment is considered a separate payment.

ii.
Any Severance Benefit under this Letter Agreement will begin only upon the date
of your “separation from service” (as defined under Section 409A(a)(2)(A)(i) of
the Code and Treas. Reg. §1.409A-1(h)) which occurs on or after the date of
termination of the employment. To the extent that the termination of your
employment does not constitute a separation from service under Section
409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-1(h) (as the result of
further services that are reasonably anticipated to be provided by you to the
Company, or any of its parents, subsidiaries or affiliates, at the time your
employment terminates), any severance benefits payable that constitute deferred
compensation under Section 409A of the Code shall be delayed until after the
date of a subsequent event constituting a separation from service under Section
409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-1(h). For purposes of
clarification, this section shall not cause any forfeiture of benefits on your
part, but shall only act as a delay until such time as a “separation from
service” occurs.

Further, if you are a “specified employee” (as that term is used in Section 409A
of the Code and regulations and other guidance issued thereunder) on the date
your separation from service becomes effective, any severance benefits payable
hereunder that constitute non-qualified deferred compensation

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under Section 409A of the Code shall be delayed until the earlier of (i) the
business day following the six-month anniversary of the date your separation
from service becomes effective, and (ii) the date of your death, but only to the
extent necessary to avoid such penalties under Section 409A of the Code. On the
earlier of (A) the business day following the six-month anniversary of the date
your separation from service becomes effective, and (B) your death, the Company
shall pay you in a lump sum the aggregate value of the non-qualified deferred
compensation that the Company otherwise would have paid you prior to that date
as described above. Neither the Company nor you shall have the right to
accelerate or defer the delivery of any such payments or benefits except to the
extent specifically permitted or required by Section 409A of the Code. The
Company makes no representation or warranty and shall have no liability to you
or any other person if any provision of this Letter Agreement is determined to
constitute deferred compensation subject to Section 409A of the Code, but do not
satisfy an exemption from, or the conditions of, Section 409A of the Code.
iii.
Sesen Bio’s obligations to make the above Severance Benefits payments will be
contingent upon your execution of and compliance with a release of claims in a
form reasonably acceptable to the Company (the “Release”), which Release must be
signed and any applicable revocation period with respect thereto must have
expired by the sixtieth (60th) day following the date of termination (i.e., last
employment day with the Company). The Severance Benefits payments shall be paid
or commence on the first payroll period following the date the waiver and
release becomes effective (the “Payment Date”). Notwithstanding the foregoing,
if the 60th day following the date of termination occurs in the calendar year
following the termination, then the Payment Date shall be no earlier than
January 1 of such subsequent calendar year. In addition, you must comply with
all post-employment obligations, including those in the Employee
Non-Competition, Non- Solicitation, Confidentiality and Assignment Agreement
that you shall sign as a condition of employment, in order to be entitled to the
Severance Benefits. In the event that you are in breach of any post-employment
obligations, the Company shall cease providing the Severance Benefits.

iv.
The Company’s obligations to pay or provide the Severance Benefits will be
contingent upon your having tendered your resignation from any position on the
Board, if applicable (and any other boards on which you serve at the request of
the Company), effective as of the date of termination.

v.
You agree to give prompt written notice of any reemployment during the Severance
Period or CIC Severance Period that results in eligibility for comparable
medical and dental benefits. If the Company makes any overpayment of COBRA
Benefits, you agree to promptly return any such overpayment to the Company. The
foregoing shall not create any obligation on your part to seek reemployment
after the date of termination of your employment.

10.    Definitions: For purposes of this Letter Agreement, “for Cause” shall
mean the Company has complied with the “Cause Process”, as defined below,
following your committing one or more of the following (each a “Cause
Condition”): (i) an act of material dishonesty involving the Company,
embezzlement, or misappropriation of assets or property of the Company; (ii)
gross negligence or willful misconduct in connection with the performance of
your duties, theft, fraud or breach of fiduciary duty to the Company; (iii) your
willful, sustained, or repeated failure to substantially perform the duties or
obligations of your position (other than due to illness or injury); (iv) a
violation of federal or state securities law; (v) the conviction of a felony or
any crime involving moral turpitude, including a plea of nolo contendere; (vi) a
material breach of any of the Company’s written policies related to conduct,
ethics, equal employment or harassment; or (vii) a material breach of your
Non-Competition, Non-Solicitation, Confidentiality and Assignment Agreement.
“Cause Process” shall mean that (i) the Company reasonably determines, in good
faith, that one of the Cause Conditions has occurred; (ii) the Company notifies
you in writing of the first occurrence of the Cause Condition within thirty (30)
days of the Board becoming aware of such condition; (iii) the Company cooperates
in good faith with your efforts, for a period not less than thirty (30) days
following such notice (the “Cause Cure Period”), to remedy the Cause Condition;
(iv) notwithstanding such efforts, the Cause Condition continues to exist; and
(v) the Company terminates your employment within thirty (30) days after the end
of the Cause Cure Period, provided that the Company will not be required to
provide a Cause Cure Period in the event that a Cause Condition (x) is of the
type described in clauses (iv), (v) or (vi) of the first sentence of this
Section 10; (y) is incapable of being cured; or (z) is required to be publicly
disclosed under applicable securities law or stock exchange rule.
If you cure to the Company’s satisfaction any Cause Condition during the
applicable Cause Cure Period, Cause shall be deemed not to have occurred. If the
Company is not required to provide a Cause Cure Period, the Cause Process will
be satisfied if the Company notifies you in writing of the first occurrence of
the Cause Condition within thirty (30) days of the Board becoming aware of such
condition and terminates your employment within thirty (30) days of such notice.
You are eligible for no more than two “cure” opportunities during your
employment.

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“Change in Control Transaction” shall mean (i) a merger or consolidation of the
Company with or into another corporation under circumstances where the
stockholders of the Company immediately prior to such merger or consolidation do
not own after such merger or consolidation shares representing at least fifty
percent (50%) of the voting power of the Company or the surviving, resulting or
parent corporation, as the case may be, (ii) a transfer of shares representing
fifty percent (50%) or more of the voting power of the Company to any person who
was not, on the Effective Date, a holder of stock of any class or preference or
any stock option of the Company, (iii) a liquidation of the Company, or (iv) a
sale or other disposition of all or substantially all of the Company’s assets.
“Good Reason” shall mean you have complied with the “Good Reason Process” as
defined below, following the occurrence of one or more of the following events:
(i) any material diminution in your duties, authority or responsibilities, (ii)
any material diminution in your Base Salary; (iii) the relocation of your
primary place of work more than fifty (50) miles from Philadelphia, PA, or (iv)
the material breach by the Company of any provision of this Letter Agreement or
any other employment-related agreement between the Company and you (as defined
below).
“Good Reason Process” shall mean that (i) you reasonably determine in good faith
that one of the foregoing “Good Reason” conditions has occurred; (ii) you notify
the Company in writing of the first occurrence of the Good Reason condition
within thirty (30) days of the first occurrence of such condition; (iii) you
cooperate in good faith with the Company’s efforts, for a period not less than
thirty (30) days following such notice (the “Cure Period”) to remedy the
condition; (iv) notwithstanding such efforts, the Good Reason condition
continues to exist; and (v) you terminate your employment within thirty (30)
days after the end of the Cure Period. If the Company cures the Good Reason
condition during the Cure Period, Good Reason shall be deemed not to have
occurred.
“Disability” shall mean your inability (as determined by the Company in good
faith) to perform the essential functions of your position due to physical or
mental disability (after taking into account the Company’s obligation to provide
reasonable accommodations in accordance with the Americans with Disabilities Act
of 1990 or analogous state law), which continues for a period of 90 days
(whether or not consecutive) during any 12-month period. In connection with any
determination regarding your possible Disability, you shall have the right to
provide to the Company, and the Company shall consider in good faith, any
physical or mental evaluation performed by a competent physician of your
selection.
11.    Modified Section 280G Cutback: Notwithstanding any other provision of
this Letter Agreement, except as set forth in Section 11.B, in the event that
the Company undergoes a “Change in Ownership or Control” (as defined below), the
following provisions shall apply:
A.
The Company shall not be obligated to provide to you any portion of any
“Contingent Compensation Payments” (as defined below) that you would otherwise
be entitled to receive to the extent necessary to eliminate any “excess
parachute payments” (as defined in Section 280G(b)(1) of the Code) for you. For
purposes of this Section 11, the Contingent Compensation Payments so eliminated
shall be referred to as the “Eliminated Payments” and the aggregate amount
(determined in accordance with Treasury Regulation Section 1.280G-1, Q/A-30 or
any successor provision) of the Contingent Compensation Payments so eliminated
shall be referred to as the “Eliminated Amount.”

B.
Notwithstanding the provisions of Section 11.A, no such reduction in Contingent
Compensation Payments shall be made if (1) the Eliminated Amount (computed
without regard to this sentence) exceeds (2) 100% of the aggregate present value
(determined in accordance with Treasury Regulation Section 1.280G-1, Q/A-31 and
Q/A-32 or any successor provisions) of the amount of any additional taxes that
would be incurred by you if the Eliminated Payments (determined without regard
to this sentence) were paid to you (including, state and federal income taxes on
the Eliminated Payments, the excise tax imposed by Section 4999 of the Code
payable with respect to all of the Contingent Compensation Payments in excess of
your “base amount” (as defined in Section 280G(b)(3) of the Code), and any
withholding taxes). The override of such reduction in Contingent Compensation
Payments pursuant to this Section 11.B shall be referred to as a “Section 11.B
Override.” For purpose of this paragraph, if any federal or state income taxes
would be attributable to the receipt of any Eliminated Payment, the amount of
such taxes shall be computed by multiplying the amount of the Eliminated Payment
by the maximum combined federal and state income tax rate provided by law.

C.
For purposes of this Section 11 the following terms shall have the following
respective meanings:

i.
“Change in Ownership or Control” shall mean a change in the ownership or
effective control of the Company or in the ownership of a substantial portion of
the assets of the Company determined in accordance with Section 280G(b)(2) of
the Code.

ii.
“Contingent Compensation Payment” shall mean any payment (or benefit) in the
nature of compensation that is made or made available (under this Letter
Agreement or otherwise) to a “disqualified

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individual” (as defined in Section 280G(c) of the Code) and that is contingent
(within the meaning of Section 280G(b)(2)(A)(i) of the Code) on a Change in
Ownership or Control of the Company.
D.
Any payments or other benefits otherwise due to you following a Change in
Ownership or Control that could reasonably be characterized (as determined by
the Company) as Contingent Compensation Payments (the “Potential Payments”)
shall not be made until the dates provided for in this Section 11.D. Within 30
days after each date on which you first become entitled to receive (whether or
not then due) a Contingent Compensation Payment relating to such Change in
Ownership or Control, the Company shall determine and notify you (with
reasonable detail regarding the basis for its determinations) (1) which
Potential Payments constitute Contingent Compensation Payments, (2) the
Eliminated Amount and (3) whether the Section 11.B Override is applicable.
Within 30 days after delivery of such notice to you, you shall deliver a
response to the Company (the “Executive Response”) stating either (A) that you
agree with the Company’s determination pursuant to the preceding sentence or (B)
that you disagrees with such determination, in which case you shall set forth
(x) which Potential Payments should be characterized as Contingent Compensation
Payments, (y) the Eliminated Amount, and (z) whether the Section 11.B Override
is applicable. In the event that you fail to deliver an Executive Response on or
before the required date, the Company’s initial determination shall be final. If
you state in the Executive Response that you agree with the Company’s
determination, the Company shall make the Potential Payments to you within three
(3) business days following delivery to the Company of the Executive Response
(except for any Potential Payments which are not due to be made until after such
date, which Potential Payments shall be made on the date on which they are due).
If you state in the Executive Response that you disagree with the Company’s
determination, then, for a period of sixty (60) days following delivery of the
Executive Response, you and the Company shall use good faith efforts to resolve
such dispute. If such dispute is not resolved within such 60-day period, such
dispute shall be settled exclusively by arbitration in Pennsylvania, in
accordance with the rules of the American Arbitration Association then in
effect. Judgment may be entered on the arbitrator’s award in any court having
jurisdiction. The Company shall, within three (3) business days following
delivery to the Company of the Executive Response, make to you those Potential
Payments as to which there is no dispute between the Company and you regarding
whether they should be made (except for any such Potential Payments which are
not due to be made until after such date, which Potential Payments shall be made
on the date on which they are due). The balance of the Potential Payments shall
be made within three (3) business days following the resolution of such dispute.

E.
The Contingent Compensation Payments to be treated as Eliminated Payments shall
be determined by the Company by determining the “Contingent Compensation Payment
Ratio” (as defined below) for each Contingent Compensation Payment and then
reducing the Contingent Compensation Payments in order beginning with the
Contingent Compensation Payment with the highest Contingent Compensation Payment
Ratio. For Contingent Compensation Payments with the same Contingent
Compensation Payment Ratio, such Contingent Compensation Payment shall be
reduced based on the time of payment of such Contingent Compensation Payments
with amounts having later payment dates being reduced first. For Contingent
Compensation Payments with the same Contingent Compensation Payment Ratio and
the same time of payment, such Contingent Compensation Payments shall be reduced
on a pro rata basis (but not below zero) prior to reducing Contingent
Compensation Payment with a lower Contingent Compensation Payment Ratio. The
term “Contingent Compensation Payment Ratio” shall mean a fraction the numerator
of which is the value of the applicable Contingent Compensation Payment that
must be taken into account by you for purposes of Section 4999(a) of the Code,
and the denominator of which is the actual amount to be received by you in
respect of the applicable Contingent Compensation Payment. For example, in the
case of an equity grant that is treated as contingent on the Change in Ownership
or Control because the time at which the payment is made or the payment vests is
accelerated, the denominator shall be determined by reference to the fair market
value of the equity at the acceleration date, and not in accordance with the
methodology for determining the value of accelerated payments set forth in
Treasury Regulation Section 1.280G-1Q/A-24(b) or (c)).

F.
The provisions of this Section 11 are intended to apply to any and all payments
or benefits available to you under this Letter Agreement or any other agreement
or plan of the Company under which you receive Contingent Compensation Payments.

12.    General: By signing below, you represent that you are not bound by any
employment contract, restrictive covenant or other restriction preventing or
limiting you from entering into employment with or performing your duties or
responsibilities for the Company, or which is in any way inconsistent with the
terms of this Letter Agreement. You also agree that you do not have in your
possession, and will not disclose to anyone at the Company, bring onto Company
premises, or use in the course of your employment at the Company at any time,
any confidential information or trade secrets belonging to any former employer
or to any other entity. You further agree that you will not, as a Sesen Bio
employee, engage in any conduct that would constitute a breach of any obligation
you may have to a former employer, including but not limited to any covenants
not to solicit or compete.

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After the Effective Date, this Letter Agreement (and Employee Non-Competition,
Non-Solicitation, Confidentiality and Assignment Agreement, the plans,
documents, and policies referenced herein) shall constitute our entire agreement
regarding the terms and conditions of your employment with the Company and shall
supersede any prior agreements or other promises or statements (whether oral or
written) regarding the terms of your employment. The terms described herein
cannot be modified except in writing by you and the Company. Failure of either
party to this Letter Agreement to insist upon strict compliance with any of the
terms, covenants or conditions hereof will not be deemed a waiver of such terms,
covenants or conditions. In the event of any inconsistency between this Letter
Agreement and any other contract between the Company and you, including the
Employee Non-Competition, Non-Solicitation, Confidentiality and Assignment
Agreement, the provisions of this Letter Agreement will prevail.

We are thrilled to have you join the leadership team at Sesen Bio. Please
contact me if you have any questions or need more information.
Sincerely,

/s/ Thomas R. Cannell            
Thomas R. Cannell, DVM
President and Chief Executive Officer

I accept the above terms of employment as stated:

/s/ Mark R. Sullivan    7/29/2019            
Mark R. Sullivan        Date

Enclosure:
•
Employee Non-Competition, Non-Solicitation, Confidentiality and Assignment
Agreement