Sec Form 4 Filing - Merck & Co., Inc. @ Harpoon Therapeutics, Inc. - 2024-03-11

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 Merck & Co., Inc. 2. Issuer Name and Ticker or Trading Symbol Harpoon Therapeutics, Inc. [ HARP] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 126 EAST LINCOLN AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 03/11/2024 (Street) RAHWAY, NJ07065 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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, par value $0.0001 03/11/2024 P 21,397,205 ( 1 ) ( 2 ) A $ 23 1,000 ( 1 ) ( 2 ) I See Footnote ( 1 ) ( 2 )

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 Merck & Co., Inc. 126 EAST LINCOLN AVENUE RAHWAY, NJ07065 X MERCK SHARP & DOHME LLC 126 EAST LINCOLN AVENUE RAHWAY, NJ07065 X Signatures /s/ Kelly E.W. Grez, Kelly E.W. Grez, Corporate Secretary 03/11/2024 Signature of Reporting Person Date /s/ Anthony Wildasin, Anthony Wildasin, Assistant Secretary 03/11/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the Agreement and Plan of Merger, dated as of January 7, 2024 by and among Merck Sharp & Dohme LLC, a wholly owned subsidiary of Merck & Co. Inc. ("Parent"), Hawaii Merger Sub, Inc., a wholly owned subsidiary of Merck Sharp & Dohme LLC ("Merger Sub"), and Harpoon Therapeutics, Inc. ("Harpoon"), Merger Sub merged with and into Harpoon (the "Merger") on March 11, 2024. Upon completion of the Merger, each share of common stock of Harpoon that was issued and outstanding immediately prior to the effective time of the Merger was cancelled, and each share of common stock of Merger Sub was converted into one share of common stock of the surviving corporation. ( 2 )(Continued from footnote 1) Consequently, upon the consummation of the Merger on March 11, 2024, Parent became the direct beneficial owner of 1,000 shares of common stock of the surviving corporation, representing 100% of the issued and outstanding shares of common stock of the surviving corporation. Merck & Co., Inc. is the indirect beneficial owner of such shares.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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