Sec Form 4 Filing - MPM BioVentures 2014, L.P. @ Harpoon Therapeutics, Inc. - 2021-02-05

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 MPM BioVentures 2014, L.P. 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) C/O MPM CAPITAL, 450 KENDALL STREET 3. Date of Earliest Transaction (MM/DD/YY) 02/05/2021 (Street) CAMBRIDGE, MA02142 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 02/05/2021 S( 1 ) 10,172 ( 2 ) D $ 20.01 ( 3 ) 3,502,885 I See Footnote ( 4 ) ( 5 ) Common Stock 02/08/2021 S( 1 ) 72,128 ( 6 ) D $ 20.04 ( 7 ) 3,430,757 I See Footnote ( 5 ) ( 8 ) Common Stock 02/09/2021 S( 1 ) 9,400 ( 9 ) D $ 20.25 ( 10 ) 3,421,357 I See Footnote ( 5 ) ( 11 ) Common Stock 3,898,422 I See Footnote ( 5 ) ( 12 )

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 Securitie s (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 MPM BioVentures 2014, L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM ASSET MANAGEMENT LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2014 (B), L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM Asset Management Investors BV2014 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2014 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2014 GP LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Foley Todd C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X GADICKE ANSBERT C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X EVNIN LUKE C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Signatures /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014, L.P. 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, Member of MPM Asset Management LLC 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014 (B), L.P. 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the manager of MPM Asset Management Investors BV2014 LLC 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC 02/09/2021 Signature of Reporting Person Date /s/ Todd Foley 02/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke 02/09/2021 Signature of Reporting Person Date /s/ Luke Evnin 02/09/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Transaction effected pursuant to a plan established pursuant to Rule 10b5-1 on 12/21/2020. ( 2 )The shares were sold as follows: 9,816 by MPM BioVentures 2014, L.P. ("BV 2014") and 356 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"). ( 3 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $19.96 to $20.11 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 4 )The shares are held as follows: 2,922,355 by BV 2014, 152,470 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 105,997 by AM BV2014 and 322,063 by MPM Asset Management LLC ("AM LLC"). MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("BV LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B). BV LLC is the manager of AM BV2014. Luke Evnin, Ansbert Gadicke and Todd Foley are the members of BV LLC and Luke Evnin and Anbert Gadicke are the members of AM LLC. ( 5 )Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its pecuniary interest therein. ( 6 )The shares were sold as follows: 69,604 by BV 2014 and 2,524 by AM BV2014. ( 7 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $19.95 to $20.28 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 8 )The shares are held as follows: 2,852,751 by BV 2014, 152,470 by BV 2014(B), 103,473 by AM BV2014 and 322,063 by AM LLC. MPM BioVentures 2014 GP LLC and BV LLC are the direct and indirect general partners of BV 2014 and BV 2014(B). BV LLC is the manager of AM BV2014. Luke Evnin, Ansbert Gadicke and Todd Foley are the members of BV LLC and Luke Evnin and Anbert Gadicke are the members of AM LLC. ( 9 )The shares were sold as follows: 9,071 by BV 2014 and 329 by AM BV2014. ( 10 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $20.00 to $2 0.54 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 11 )The shares are held as follows: 2,843,680 by BV 2014, 152,470 by BV 2014(B), 103,144 by AM BV2014 and 322,063 by AM LLC. MPM BioVentures 2014 GP LLC and BV LLC are the direct and indirect general partners of BV 2014 and BV 2014(B). BV LLC is the manager of AM BV2014. Luke Evnin, Ansbert Gadicke and Todd Foley are the members of BV LLC and Luke Evnin and Anbert Gadicke are the members of AM LLC. ( 12 )The reported securities are held in the account of UBS Oncology Impact Fund L.P. ("UBS Oncology"). MPM Oncology Impact Management GP LLC ("Oncology GP LLC") is the General Partner of MPM Oncology Impact Management LP, the General Partner of Oncology Impact Fund (Cayman) Management L.P., the General Partner of UBS Oncology. Ansbert Gadicke is the Managing Member of Oncology GP LLC.

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