Sec Form 4 Filing - Omega Fund V, L.P. @ Gossamer Bio, Inc. - 2019-09-05

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 Omega Fund V, L.P. 2. Issuer Name and Ticker or Trading Symbol Gossamer Bio, Inc. [ GOSS] 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) 888 BOYLSTON STREET, SUITE 1111 3. Date of Earliest Transaction (MM/DD/YY) 09/05/2019 (Street) BOSTON, MA02199 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 09/05/2019 S 12,704 D $ 21.6022 ( 1 ) 6,940,712 D ( 3 ) Common Stock 09/06/2019 S 8,700 D $ 21.5061 ( 2 ) 6,932,012 D ( 3 )

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 Omega Fund V, L.P. 888 BOYLSTON STREET, SUITE 1111 BOSTON, MA02199 X Omega Fund V GP, L.P. 888 BOYLSTON STREET, SUITE 1111 BOSTON, MA02199 X Omega Fund V GP Manager, Ltd. 888 BOYLSTON STREET, SUITE 1111 BOSTON, MA02199 X Stampacchia Otello 185 DARTMOUTH STREET BOSTON, MA02116 X X Signatures /s/ Anne-Mari Paster, as an authorized signatory of each Reporting Person 09/09/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $21.50 to $21.87 per share, inclusive. ( 2 )The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $21.50 to $21.56 per share, inclusive. ( 3 )The reported securities are held directly by Omega Fund V, L.P. ("Omega V"). The reported securities may be deemed to be beneficially owned by each of Omega Fund V GP, L.P. ("Omega V GP"), as the general partner of Omega V, and Omega Fund V GP Manager, Ltd. ("Omega V GP Manager"), as the general partner of Omega V GP. Otello Stampacchia, Richard Lim, Anne-Mari Paster and Claudio Nessi (the "Omega Directors") are all the shareholders and directors of Omega V GP Manager and have shared voting and investment power over the shares held by Omega V. Each of Omega V GP, Omega Fund V GP Manager and the Omega Directors disclaims beneficial ownership of the securities reported herein, except to the extent of its or their pecuniary interest therein, if any. Otello Stampacchia is also a member of the issuer's board of directors.

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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