Washington, D.C. 20549
Pursuant to Section 13 OR 15 (d)
of the Securities Exchange Act of 1934
Date of Report (Date of earliest event reported): February 17, 2021
(Exact name of registrant as specified in its charter)
(State or other jurisdiction
of incorporation)
File Number)
(I.R.S. Employer
Identification No.)
245 First Street, Suite 1800
Cambridge, MA
(Address of principal executive offices)(Zip Code)
Registrant’s telephone number, including area code: (617) 444-8550
Not Applicable
(Former name or former address, if changed since last report.)
Check the appropriate box below if the Form 8–K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
Soliciting material pursuant to Rule 14a–12 under the Exchange Act (17 CFR 240.14a–12)
Pre–commencement communications pursuant to Rule 14d–2(b) under the Exchange Act (17 CFR 240.14d–2(b))
Pre–commencement communications pursuant to Rule 13e–4(c) under the Exchange Act (17 CFR 240.13e–4(c))
Title of each classTrading Symbol(s)Name of each exchange on which registered
Common Stock, par value $0.001SESNThe Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).
                            Emerging growth company     

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.                                 ¨

Item 1.01 – Entry into a Material Definitive Agreement.

On February 17, 2021, Sesen Bio, Inc. (the “Company”) entered into Amendment No. 2 (the “Second Amendment”) to the Open Market Sale AgreementSM, dated November 29, 2019, as amended by Amendment No. 1 to the Open Market Sale AgreementSM, dated October 30, 2020 (the “Sale Agreement”) with Jefferies LLC, as sales agent (“Jefferies”). The Second Amendment allows for the Company to issue and sell through Jefferies up to an additional $34.5 million of shares of its common stock, par value $0.001 per share (“Common Stock”), under the Sale Agreement. As a result of the Second Amendment, the Company now has approximately $35.5 million in total remaining capacity under the Sale Agreement, which the Company may sell efficiently from time to time over the coming months.
This description of the Second Amendment does not purport to be complete and is qualified in its entirety by reference to the Second Amendment, which is attached hereto as Exhibit 1.1 and incorporated by reference herein.
The Common Stock to be sold under the Sale Agreement, if any, will be issued and sold pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-223750), previously filed with the Securities and Exchange Commission (“SEC”) on March 19, 2018, and subsequently amended on May 16, 2018, and declared effective by the SEC on June 8, 2018. On February 17, 2021, the Company filed a prospectus supplement (the “Prospectus Supplement”) with the SEC in connection with the offer and sale of the Common Stock pursuant to the Sale Agreement, as amended by the Second Amendment. The Prospectus Supplement supersedes, and the Company has ceased the use of and the offering of shares of Common Stock under, the Company’s prior prospectus supplement dated October 30, 2020. This Current Report on Form 8-K shall not constitute an offer to sell or the solicitation of an offer to buy the Common Stock nor shall there be any sale of the Common Stock in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or other jurisdiction
The legal opinion of Hogan Lovells US LLP relating to the legality of the issuance and sale of the Common Stock is attached as Exhibit 5.1 to this Current Report on Form 8-K and is incorporated by reference herein.
This Current Report on Form 8-K contains forward-looking statements, including, but not limited to, the Company’s intentions or ability to sell shares of Common Stock efficiently pursuant to the Sale Agreement. These forward-looking statements are based on the Company’s current expectations and inherently involve significant risks and uncertainties. The Company’s actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties. A further description of the risks and uncertainties relating to the business of the Company is contained in the Company’s most recent annual report on Form 10-K and the Company’s quarterly reports on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC. The Company undertakes no duty or obligation to update any forward-looking statements contained in this report as a result of new information, future events or changes in its expectations.

Item 9.01 - Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No.Description

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
Date: February 17, 2021
Sesen Bio, Inc.
By:/s/ Thomas R. Cannell, D.V.M.
Thomas R. Cannell, D.V.M.
President and Chief Executive Officer

AMENDMENT NO. 2 TO THE OPEN MARKET SALE AGREEMENTSM February 17, 2021 JEFFERIES LLC 520 Madison Avenue New York, New York 10022 Ladies and Gentlemen: This Amendment No. 2 to the Open Market Sale AgreementSM (this “Amendment”) is entered into as of the date first written above by Sesen Bio, Inc., a Delaware corporation (the “Company”), and Jefferies LLC (“Agent”), that are parties to that certain Open Market Sale AgreementSM, dated November 29, 2019, as amended by Amendment No. 1, dated October 30, 2020 (collectively, the “Original Agreement”). All capitalized terms not defined herein shall have the meanings ascribed to them in the Original Agreement. The parties, intending to be legally bound, hereby amend the Original Agreement as follows: 1. The preamble to the Original Agreement is hereby deleted in its entirety and replaced with the following: Sesen Bio, Inc., a Delaware corporation (the “Company”), proposes, subject to the terms and conditions stated herein, to issue and sell from time to time through Jefferies LLC, as sales agent and/or principal (the “Agent”), shares of the Company’s common stock, par value $0.001 per share (the “Common Shares”), having an aggregate offering price of up to $119.5 million on the terms set forth in this agreement (this “Agreement”). 2. The Company represents and warrants to, and agrees with the Agent that: (a) this Amendment has been duly authorized, executed and delivered by, and is a valid and binding agreement of, the Company, enforceable in accordance with its terms, except as rights to indemnification hereunder may be limited by applicable law and except as the enforcement hereof may be limited by bankruptcy, insolvency, reorganization, moratorium or other similar laws relating to or affecting the rights and remedies of creditors or by general equitable principles; and (b) that on the date hereof, the Company will file a prospectus supplement with respect to the Shares and that the filing of such a prospectus supplement constitutes a Triggering Event Date on which the Company is required to provide a certificate pursuant to Section 4(o) of the Original Agreement (including, without limitation, for purposes of expense reimbursement as provided for in Section 3(d) of the Original Agreement). 3. This Amendment together with the Original Agreement (including all schedules and exhibits attached thereto and Placement Notices issued pursuant hereto and thereto) constitutes the entire agreement and supersedes all other prior and contemporaneous agreements and undertakings, both written and oral, among the parties hereto with regard to the subject matter hereof. Neither this Amendment nor any term hereof may be amended except pursuant to a written instrument executed by the Company and the Agent. In the event that any one or more of the provisions contained herein, or the application thereof in any circumstance, is held invalid, illegal or unenforceable as written by a court of competent jurisdiction, then such provision shall be given full force and effect to the fullest possible extent that it is valid, legal and enforceable, and the

2 remainder of the terms and provisions herein shall be construed as if such invalid, illegal or unenforceable term or provision was not contained herein, but only to the extent that giving effect to such provision and the remainder of the terms and provisions hereof shall be in accordance with the intent of the parties as reflected in this Amendment. All references in the Original Agreement to the “Agreement” shall mean the Original Agreement as amended by this Amendment; provided, however, that all references to “date of this Agreement” in the Original Agreement shall continue to refer to the date of the Original Agreement. 4. This Amendment shall be governed by and construed in accordance with the internal laws of the State of New York applicable to agreements made and to be performed in such state. Any legal suit, action or proceeding arising out of or based upon this Amendment or the transactions contemplated hereby (“Related Proceedings”) may be instituted in the federal courts of the United States of America located in the Borough of Manhattan in the City of New York or the courts of the State of New York in each case located in the Borough of Manhattan in the City of New York (collectively, the “Specified Courts”), and each party irrevocably submits to the exclusive jurisdiction (except for proceedings instituted in regard to the enforcement of a judgment of any such court (a “Related Judgment”), as to which such jurisdiction is non-exclusive) of such courts in any such suit, action or proceeding. Service of any process, summons, notice or document by mail to such party’s address set forth above shall be effective service of process for any suit, action or other proceeding brought in any such court. The parties irrevocably and unconditionally waive any objection to the laying of venue of any suit, action or other proceeding in the Specified Courts and irrevocably and unconditionally waive and agree not to plead or claim in any such court that any such suit, action or other proceeding brought in any such court has been brought in an inconvenient forum. The provisions of this paragraph shall survive any termination of this Amendment. 5. This Amendment may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Delivery of an executed amendment by one party to the other may be made by facsimile transmission or electronic transmission (e.g., PDF). [Remainder of Page Intentionally Blank]

[Signature Page to Amendment No. 2 to the Sales Agreement] If the foregoing correctly sets forth the understanding between the Company and the Agent, please so indicate in the space provided below for that purpose, whereupon this letter shall constitute a binding amendment to the Original Agreement between the Company and the Agent. Very truly yours, JEFFERIES LLC By: /s/ Michael Magarro Name: Michael Magarro Title: Managing Director ACCEPTED as of the date first-above written: SESEN BIO, INC. By: /s/ Thomas R. Cannell, D.V.M. Name: Thomas R. Cannell, D.V.M. Title: President and Chief Executive Officer

Exhibit 5. 1 Hogan Lovells US LLP is a limited liability partnership registered in the District of Columbia. “Hogan Lovells” is an international legal practice that includes Hogan Lovells US LLP and Hogan Lovells International LLP, with offices in: Alicante Amsterdam Baltimore Beijing Birmingham Boston Brussels Colorado Springs Denver Dubai Dusseldorf Frankfurt Hamburg Hanoi Ho Chi Minh City Hong Kong Houston Johannesburg London Los Angeles Luxembourg Madrid Mexico City Miami Milan Minneapolis Monterrey Moscow Munich New York Northern Virginia Paris Perth Philadelphia Rome San Francisco São Paulo Shanghai Silicon Valley Singapore Sydney Tokyo Warsaw Washington, D.C. Associated Offices: Budapest Jakarta Riyadh Shanghai FTZ Ulaanbaatar Zagreb. Business Service Centers: Johannesburg Louisville. Legal Services Center: Berlin. For more information see Hogan Lovells US LLP 1735 Market Street, Floor 23 Philadelphia, PA 19103 T +1 267 675 4600 F +1 267 675 4601 February 17, 2021 Board of Directors Sesen Bio, Inc. 245 First Street, Suite 1800 Cambridge, MA 02142 Ladies and Gentlemen: We are acting as counsel to Sesen Bio, Inc., a Delaware corporation (the “Company”), in connection with the issuance and sale of up to $35,500,000 of shares of common stock, par value $0.001 per share, of the Company (the “Shares”), from time to time and at various prices in an “at the market offering” pursuant to the terms of the Open Market Sale AgreementSM, dated November 29, 2019, as amended by Amendment No. 1 to the Open Market Sale AgreementSM, dated October 30, 2020 and Amendment No. 2 to the Open Market Sale AgreementSM, dated February 17, 2021 (the “Agreement”), between the Company and Jefferies LLC, as placement agent (the “Agent”). The offering of the Shares by the Company is being made pursuant to its registration statement on Form S-3, as amended (file no. 333-223750) (the “Registration Statement”), filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Act”), the accompanying prospectus dated June 8, 2018 (the “Base Prospectus”) that forms a part thereof and the Prospectus Supplement dated February 17, 2021 (the “Prospectus Supplement” and together with the Base Prospectus, the “Prospectus”). This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement. For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to us as copies (including pdfs). As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing. This opinion letter is based as to matters of law solely on the Delaware General Corporation Law, as amended. We express no opinion herein as to any other statutes, rules or regulations. Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) execution and delivery by the Company of the Agreement, (ii) issuance of the Shares pursuant to the terms of

Sesen Bio, Inc. - 2 - February 17, 2021 the Agreement, and (iii) receipt by the Company of the consideration for the Shares specified in the resolutions of the Pricing Committee of the Board of Directors, the Shares will be validly issued, fully paid, and nonassessable. This opinion letter has been prepared for use in connection with the filing by the Company of a Current Report on Form 8-K on the date hereof relating to the offer and sale of the Shares, which Form 8-K will be incorporated by reference into the Registration Statement and Prospectus, and speaks as of the date hereof. We assume no obligation to advise you of any changes in the foregoing subsequent to the delivery of this letter. We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Company’s Current Report on Form 8-K filed on the date hereof and to the reference to this firm under the caption “Legal Matters” in the Prospectus constituting a part of the Registration Statement. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Act. Very truly yours, /s/ HOGAN LOVELLS US LLP HOGAN LOVELLS US LLP