Sec Form 4 Filing - CROCKER GARY L @ MERRIMACK PHARMACEUTICALS INC - 2020-07-22

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person CROCKER GARY L 2. Issuer Name and Ticker or Trading Symbol MERRIMACK PHARMACEUTICALS INC [ MACK] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) See Remarks (Last) (First) (Middle) C/O MERRIMACK PHARMACEUTICALS, INC., ONE BROADWAY 14TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 07/22/2020 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 07/22/2020 S 17,000 D ( 6 ) ( 7 ) $ 3.202 0 D ( 1 ) Common Stock 07/22/2020 S 5,986 D ( 6 ) ( 7 ) $ 3.0419 0 D ( 1 ) Common Stock 07/22/2020 S 8,428 D ( 6 ) ( 7 ) $ 3.202 0 D ( 2 ) Common Stock 07/22/2020 S 86,549 D ( 6 ) ( 7 ) $ 3.0419 0 D ( 2 ) Common Stock 07/22/2020 S 52,068 D ( 6 ) ( 7 ) $ 3.0419 0 I See Footnote ( 3 ) Common Stock 07/22/2020 S 17,250 D ( 6 ) ( 7 ) $ 3.202 0 I See Footnote ( 4 ) Common Stock 07/2 2/2020 S 6,228 D ( 6 ) ( 7 ) $ 3.202 0 I See Footnote ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other CROCKER GARY L C/O MERRIMACK PHARMACEUTICALS, INC. ONE BROADWAY 14TH FLOOR CAMBRIDGE, MA02142 X See Remarks Signatures /s/ Gary L. Crocker 07/24/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Shares held directly by Reporting Person. ( 2 )Shares held jointly with Reporting Person's wife. ( 3 )Shares held directly by Reporting Person's wife. ( 4 )Shares held by Crocker Family Investments, LLC, over which Reporting Person is the Managing Member. ( 5 )Shares held by Crocker Ventures, LLC, over which Reporting Person is the President and Managing Member. ( 6 )The sale of the securities referenced in this From 4 were conducted in a private transaction between Gary Crocker and certain family members and affiliates as the sellers and each of Western Standard Partners, L.P., Western Standard Partners QP, L.P., Newtyn Partners, LP, and Newton Partners TE, LP as the purchasers, regarding all shares of the Company over which he had dispositive control, along with the record owners of most of the shares of the Company over which Reporting Person had voting control. The purpose of the sale was to minimize tax liability by matching losses from these sales of Company stock with other investment gains. Gary Crocker is President and Chairman of Merrimack Pharmaceuticals, Inc. (the "Company"). Eric Andersen, a member of the Company's Board of Directors, is Managing Member of Western Standard LLC, the investment manager for each of Western Standard Partners L.P. and Western Standard Partners QP L.P. ( 7 )(continued from footnote 6) Noah Levy, a member of the Company's Board of Directors, is Managing Member of Newtyn Management, LLC, the investment manager for Newtyn Partners, LP, and Newton Partners TE, LP.

Remarks: In addition to the sale of securities referenced in Table I of this Form 4, 161,039 shares held by certain trusts established for members of Reporting Person's family, certain entities controlled by members of his family and certain individual members of his family, and in which Reporting Person has no pecuniary interest, were also sold to the purchasers (111,453 shares at a price of $3.2020 per share, and 49,586 shares at a price of $3.0419 per share). Such holders were parties to a Shareholder Voting Agreement dated December 20, 2010, pursuant to which the parties to the agreement had agreed to vote his, her or its shares as directed by Crocker Ventures, LLC. Reporting Person is the President and Managing Member of Crocker Ventures, LLC and in connection therewith shared voting control over all the shares subject to the Shareholder Voting Agreement. In connection with the disposition of shares disclosed herein, the Shareholder Voting Agreement has been terminated and thus the Reporting Person no longer shares voting control of any shares held by third parties.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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