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•	Accounting policy election to use the short-term lease exception by asset class;

•	Election of the practical expedient package during transition, which includes:

–	An entity need not reassess whether any expired or existing contracts are or contain leases;

–	An entity need not reassess the classification for any expired or existing leases. As a result, all leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases under ASC 842, and all leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases under ASC 842; and

–	An entity need not reassess initial direct costs for any existing leases.

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Level 1:	Inputs are quoted prices for identical instruments in active markets,

Level 2:	Inputs are quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; or model-derived valuations whose inputs are observable or whose significant value drivers are observable.

Level 3:	Inputs are unobservable and reflect the Company’s own assumptions, based on the best information available, including the Company’s own data.

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1.

An operating lease for its manufacturing facility in Winnipeg, Manitoba, which consists of a 31,100 square foot manufacturing, laboratory, warehouse and office facility, under a five-year renewable lease through September 2020 with a right to renew the lease for one subsequent five-year term. The minimum monthly rent under this lease is $12,600 per month. In addition to rent expense, the Company expects to incur $12,300 per month in related operating expenses. Operating lease cost under this lease, including the related operating costs, was $76,000 and $222,000 for the three and nine months ended September 30, 2019, respectively. Previously under ASC 840, rent expense for this lease, including related operating costs, was $78,000 and $239,000 for the three and nine months ended September 30, 2018, respectively.

2.

A short-term property lease for its current corporate headquarters in Cambridge, MA that extends through December 31, 2019. The minimum monthly rent for this office space is $7,900 per month. The Company recorded $24,000 and $75,000 in short-term lease cost for the three and nine months ended September 30, 2019, respectively. Previously under ASC 840, the Company recorded $35,000 and $97,000 in rent expense for the three and nine months ended September 30, 2018, respectively, for this lease; and

3.

A short-term property lease for office space in Philadelphia, PA that extends through December 31, 2019. Currently, the minimum monthly rent under this lease is $11,000 per month. The Company recorded $35,000 and $113,000 in short term lease cost for the three and nine months ended September 30, 2019, respectively. Previously under ASC 840, the Company recorded $36,000 and $92,000 in rent expense for the three and nine months ended September 30, 2018, respectively, for this lease.

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•	Cohort 1 (n=86): Patients with carcinoma in situ ("CIS") with or without papillary disease that recurred within six months of their last course of adequate BCG

•	Cohort 2 (n=7): Patients with CIS with or without papillary disease that was determined to be refractory or recurred after six months, but less than 11 months, after their last course of adequate BCG

•	Cohort 3 (n=40): Patients with high-risk papillary disease without CIS that was determined to be refractory or recurred within six months of their last course of adequate BCG

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•

Duration of Response: The median duration of response for patients in Cohort 1 and Cohort 2 combined (n=93) is 287 days (95% confidence interval ("CI"), 154-not estimable ("NE")), using the Kaplan-Meier method. The Kaplan-Meier method is a non-parametric statistical analysis used to estimate survival times and times to event when incomplete observations in data exist. Additional ad hoc analysis of pooled data for all patients with CIS (Cohorts 1 and 2, n=93) shows that among patients who achieved a complete response at 3 months, 52% remained disease-free for a total of 12 months or longer after starting treatment, using the Kaplan-Meier method.

•	Time to Disease Recurrence: High-grade papillary (Ta or T1) NMIBC is associated with higher rates of progression and recurrence. Therefore, time to disease recurrence is a key secondary endpoint for patients with high-risk papillary-only NMIBC. The median time to disease recurrence for patients in Cohort 3 (n=40) is 402 days (95% CI, 170-NE), using the Kaplan-Meier method.

•

Time to Cystectomy: The first 2018 United States Food and Drug Administration ("FDA") guidance on treatment of BCG-unresponsive NMIBC patients states that the goal of therapy in such patients is to avoid cystectomy. Therefore, time to cystectomy is a key secondary endpoint in the VISTA Trial. Across all 133 patients treated with Vicinium in the VISTA Trial, greater than 75% of all patients are estimated to remain cystectomy-free at 2.5 years, using the Kaplan-Meier method. Additional ad hoc analysis of responders and non-responders for all patients shows that approximately 88% of responders are estimated to remain cystectomy-free at 3 years.

•	Progression-Free Survival: 90% of all 133 patients treated with Vicinium in the VISTA Trial are estimated to remain progression-free for 2 years or greater, using the Kaplan-Meier method. Progression-free is defined as the time from the date of first dose of study treatment to disease progression (e.g. T2 or more advanced disease) or death as a first event.

•	Event-Free Survival: 29% of all 133 patients treated with Vicinium in the VISTA Trial are estimated to remain event-free at 12 months, using the Kaplan-Meier method. Event-free survival is defined as the time from the date of first dose of study treatment to disease recurrence, progression, or death as a first event.

•	Overall Survival: 96% of all 133 patients treated with Vicinium in the VISTA Trial are estimated to have an overall survival of 2 years or greater, using the Kaplan-Meier method. Overall survival is defined as the time from the date of first dose of study treatment to death from any cause.

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•	employee-related expenses, including salaries, benefits, travel and share-based compensation expense;

•	expenses incurred under agreements with contract research organizations ("CROs") and investigative sites that conduct our clinical trials;

•	expenses associated with developing manufacturing capabilities and manufacturing clinical study materials;

•	expenses associated with transferring manufacturing capabilities to contract manufacturing organizations ("CMOs") for commercial-scale production;

•	facilities, depreciation, and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, insurance, and other supplies; and

•	expenses associated with pre-clinical and regulatory activities.

•	the scope, progress, outcome and costs of our clinical trials and other research and development activities;

•	the efficacy and potential advantages of our product candidates compared to alternative treatments, including any standard of care;

•	the market acceptance of our product candidates;

•	the cost and timing of the implementation of commercial-scale manufacturing of our product candidates;

•	obtaining, maintaining, defending and enforcing patent claims and other intellectual property rights;

•	significant and changing government regulation; and

•	the timing, receipt and terms of any marketing approvals.

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•	continue our Phase 3 clinical trial for Vicinium for the treatment of high-risk NMIBC;

•	seek marketing approvals for any product candidates that successfully complete clinical trials;

•	establish sales, marketing and distribution capabilities and scale up and validate external manufacturing capabilities (including initiating and completing the manufacturing process and technology transfer to any third-party manufacturers) to commercialize any products for which we may obtain marketing approval;

•	maintain, expand and protect our intellectual property portfolio;

•	add equipment and physical infrastructure to support our research and development;

•	hire additional clinical, regulatory, quality control, scientific and management personnel;

•	expand our operational, financial and management systems and personnel;

•	conduct research and pre-clinical and clinical development of our other product candidates;

•	seek to discover and develop additional product candidates; and

•	in-license or acquire the rights to other products, product candidates or technologies.

•	the scope, initiation, progress, timing, costs and results of pre-clinical development and laboratory testing and clinical trials for our product candidates;

•	the cost and timing of any new clinical trials or studies of our product candidates;

•	our ability to establish collaborations or licensing arrangements on favorable terms, if at all, particularly manufacturing, marketing and distribution arrangements for our product candidates;

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•	the costs and timing of the implementation of commercial-scale manufacturing activities, including those associated with the manufacturing process and technology transfer to third-party manufacturers to facilitate such commercial-scale manufacturing;

•	the costs and timing of establishing sales, marketing and distribution capabilities for any product candidates for which we may receive regulatory approval;

•	the costs and timing of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property rights and defending any intellectual property-related claims;

•	our obligation to make milestone, royalty and other payments to third-party licensors under our licensing agreements;

•	the extent to which we in-license or acquire rights to other products, product candidates or technologies;

•	the outcome, timing and cost of regulatory review by the FDA and comparable foreign regulatory authorities, including the potential for the FDA or comparable foreign regulatory authorities, including Health Canada, to require that we perform more studies than those that we currently expect to perform;

•	our ability to achieve certain future regulatory, development and commercialization milestones under the License Agreement with Roche;

•	the effect of competing technological and market developments; and

•	the revenue, if any, received from commercial sales of any product candidates for which we receive regulatory approval.

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Item 1A.	Risk Factors.

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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.

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.

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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.

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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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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.

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

1.	Grant of Option.

2.	Vesting Schedule.

3.	Exercise of Option.

(a)	Form of Exercise. Each election to exercise this option shall be in writing, signed by the Participant (or such electronic notice as is approved by the Company), and received by the Company at its principal office, accompanied by this agreement and payment in full as follows:

(1)	in cash or by check, payable to the order of the Company;

(2)

by (i) delivery of an irrevocable and unconditional undertaking by a creditworthy broker to deliver promptly to the Company sufficient funds to pay the exercise price and any required tax withholding or (ii) delivery by the Participant to the Company of a copy of irrevocable and unconditional instructions to a creditworthy broker to deliver promptly to the Company cash or a check sufficient to pay the exercise price and any required tax withholding;

(3)

to the extent approved by the Board of Directors of the Company (the “Board”), in its sole discretion, by delivery (either by actual delivery or attestation) of shares of Common Stock owned by the Participant valued at their fair market value per share as determined by (or in a manner approved by) the Board (the “Fair Market Value”), provided (i) such method of payment is then permitted under applicable law, (ii) such Common Stock, if acquired directly from the Company, was owned by the Participant for such minimum period of time, if any, as may be established by the Board in its discretion and (iii) such Common Stock is not subject to any repurchase, forfeiture, unfulfilled vesting or other similar requirements;

(4)

to the extent approved by the Board, in its sole discretion, by delivery of a notice of “net exercise” to the Company, as a result of which the Participant would receive (i) the number of shares underlying the portion of this being exercised, less (ii) such number of shares as is equal to (A) the aggregate exercise price for the portion of this option being exercised divided by (B) the Fair Market Value on the date of exercise;

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(5)	to the extent permitted by applicable law or approved by the Board, in its sole discretion, by payment of such other lawful consideration as the Board may determine; or

(6)	by any combination of the above permitted forms of payment.

(b)

Continuous Relationship with the Company Required. Except as otherwise provided in this Section 3, this option may not be exercised unless the Participant, at the time he exercises this option, is, and has been at all times since the Grant Date, an employee, officer or a director of, or consultant or advisor to, the Company or any other entity the employees, officers, directors, consultants, or advisors of which are eligible to receive option grants under the Plan (an “Eligible Participant”).

(c)

Termination of Relationship with the Company. If the Participant ceases to be an Eligible Participant for any reason, then, except as provided in paragraphs (d) and (e) below, the right to exercise this option shall terminate three months after such cessation (but in no event after the Final Exercise Date), provided that this option shall be exercisable only to the extent that the Participant was entitled to exercise this option on the date of such cessation.

(d)

Exercise Period Upon Death or Disability. If the Participant dies or becomes disabled (within the meaning of Section 22(e)(3) of the Code) prior to the Final Exercise Date while he is an Eligible Participant and the Company has not terminated such relationship for “cause” as specified in paragraph (e) below, this option shall be exercisable, within the period of one year following the date of death or disability of the Participant, by the Participant (or in the case of death by an authorized transferee), provided that this option shall be exercisable only to the extent that this option was exercisable by the Participant on the date of his death or disability, and further provided that this option shall not be exercisable after the Final Exercise Date.

(e)	Termination for Cause. If the Participant, prior to the Final Exercise Date, is terminated by the Company for Cause (as defined in the Letter Agreement, dated as of August 1, 2019 between the Participant and the Company, or any successor agreement thereto (the “Letter Agreement”)), the right to exercise this option shall terminate immediately upon the effective date of such termination.

(f)

Letter Agreement. Notwithstanding anything to the contrary in this Section 3 or in Section 7, this option shall be subject to any applicable vesting terms set forth in the Letter Agreement, including the accelerated vesting provisions set forth in the Letter Agreement applicable in connection with certain terminations within the specified period following a Change in Control Transaction (as defined in the Letter Agreement).

4.	Agreement in Connection with Public Offering.

5.	Withholding.

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6.	Transfer Restrictions.

7.	Adjustments for Changes in Common Stock and Certain Other Events.

(a)

Changes in Capitalization. In the event of any stock split, reverse stock split, stock dividend, recapitalization, combination of shares, reclassification of shares, spin-off or other similar change in capitalization or event, or any dividend or distribution to holders of Common Stock other than an ordinary cash dividend, the number and class of securities and exercise price per share of this option shall be equitably adjusted by the Company in the manner determined by the Board.  Without limiting the generality of the foregoing, in the event the Company effects a split of the Common Stock by means of a stock dividend and the exercise price of and the number of shares subject to this option are adjusted as of the date of the distribution of the dividend (rather than as of the record date for such dividend), then the Participant, if he exercises this option between the record date and the distribution date for such stock dividend, shall be entitled to receive, on the distribution date, the stock dividend with respect to the shares of Common Stock acquired upon exercise of this option, notwithstanding the fact that such shares were not outstanding as of the close of business on the record date for such stock dividend.

(b)

Reorganization Events. A “Reorganization Event” shall mean:  (a) any merger or consolidation of the Company with or into another entity as a result of which all of the Common Stock of the Company is converted into or exchanged for the right to receive cash, securities or other property or is cancelled, (b) any transfer or disposition of all of the Common Stock of the Company for cash, securities or other property pursuant to a share exchange or other transaction or (c) any liquidation or dissolution of the Company.  In connection with a Reorganization Event, the Board may take any one or more of the following actions with respect to this option (or any portion thereof) on such terms as the Board determines: (i) provide that this option shall be assumed, or substantially equivalent option shall be substituted, by the acquiring or succeeding corporation (or an affiliate thereof), (ii) upon written notice to the Participant, provide that the unvested and/ or unexercised portion of this option will terminate immediately prior to the consummation of such Reorganization Event unless exercised by the Participant within a specified period following the date of such notice, (iii) provide that this option shall become exercisable, realizable, or deliverable, or restrictions applicable to this option shall lapse, in whole or in part prior to or upon such Reorganization Event, (iv) in the event of a Reorganization Event under the terms of which holders of Common Stock will receive upon consummation thereof a cash payment for each share surrendered in the Reorganization Event (the “Acquisition Price”), make or provide for a cash payment to the Participant with respect to this option equal to (A) the number of shares of Common Stock subject to the vested portion of this option (after giving effect to any acceleration of vesting that occurs upon or immediately prior to such Reorganization Event) multiplied by (B) the excess, if any, of (I) the Acquisition Price over (II) the exercise price of this option and any applicable tax withholdings, in exchange

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8.	Miscellaneous.

(a)

No Right To Employment or Other Status. The grant of this option shall not be construed as giving the Participant the right to continued employment or any other relationship with the Company.  The Company expressly reserves the right at any time to dismiss or otherwise terminate its relationship with the Participant free from any liability or claim hereunder, except as otherwise expressly provided herein or provided for in the Letter Agreement.

(b)	No Rights As Stockholder. Subject to the provisions of this option, the  Participant shall not have any rights as a stockholder with respect to any shares of Common Stock to be distributed with respect to this option until becoming the record holder of such shares.

(c)	Entire Agreement. This Agreement, together with the Letter Agreement, constitute the entire agreement between the parties, and supersede all prior agreements and understandings, relating to the subject matter hereof.

(d)

Amendment. Except with respect to any vesting terms set forth in the Letter Agreement, the Board may amend, modify or terminate this Agreement, including but not limited to, substituting another option of the same or a different type and changing the date of exercise or realization.  Notwithstanding the foregoing, the Participant’s consent to such action shall be required unless (i) the Board determines that the action, taking into account any related action, would not materially and adversely affect the Participant, or (ii) the change is permitted under Section 7 and the Letter Agreement.

(e)	Acceleration. The Board may at any time provide that this option shall become immediately exercisable in whole or in part, free of some or all restrictions or conditions, or otherwise realizable in whole or in part, as the case may be.

(f)

Conditions on Delivery of Stock. The Company will not be obligated to deliver any shares of Common Stock pursuant to this Agreement until (i) all conditions of this Agreement have been met to the satisfaction of the Company, (ii) in the opinion of the Company’s counsel, all other legal matters in connection with the issuance and delivery of such shares have been satisfied, including any applicable securities laws and regulations and any applicable stock exchange or stock market rules and regulations, and (iii) the Participant has executed and delivered to the Company such representations or agreements as the Company may consider appropriate to satisfy the requirements of any applicable laws, rules or regulations.

(g)

Administration by Board. The Board will administer this Agreement and may construe and interpret the terms hereof.  Subject to the terms and provisions of the Letter Agreement, the Board may correct any defect, supply any omission or reconcile any inconsistency in this Agreement in the manner and to the extent it shall deem expedient to carry the Agreement into effect and it shall be the sole and final judge of such expediency.  No director or person acting pursuant to the authority delegated by the Board shall be liable for any action or determination relating to or under this Agreement made in good faith.

(h)	Appointment of Committees. To the extent permitted by applicable law, the Board may delegate any or all of its powers hereunder to one or more committees or subcommittees of the Board (a “Committee”).  All references herein to the “Board” shall mean the Board or a Committee to the extent that the Board’s powers or authority hereunder have been delegated to such Committee.

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(i)	Severability. The invalidity or unenforceability of any provision hereof shall not affect the validity or enforceability of any other provision hereof, and each such other provision shall be severable and enforceable to the extent permitted by law.

(j)	Governing Law. This Agreement shall be governed by and interpreted in accordance with the laws of the State of Delaware, excluding choice-of-law principles of the law of such state that would require the application of the laws of a jurisdiction other than the State of Delaware.

(k)	Counterparts. This Agreement may be executed in one or more counterparts, each of which shall be deemed to be an original but all of which together will constitute one in the same instrument.

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1.	I have reviewed this Quarterly Report on Form 10-Q for the fiscal quarter ended September 30, 2019 of Sesen Bio, Inc.;

2.	Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3.	Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4.	The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)	Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)	Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)	Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)	Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5.	The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)	all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)	any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

1.	I have reviewed this Quarterly Report on Form 10-Q for the fiscal quarter ended September 30, 2019 of Sesen Bio, Inc.;

2.	Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3.	Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4.	The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)	Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)	Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)	Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)	Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5.	The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)	all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)	any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

(1)	the Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)	the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

(1)	the Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)	the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.