Sec Form 3 Filing - Thompson Peter A. @ Principia Biopharma Inc. - 2018-09-13

FORM 3 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 Thompson Peter A. 2. Issuer Name and Ticker or Trading Symbol Principia Biopharma Inc. [ PRNB] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O PRINCIPIA BIOPHARMA INC., 400 EAST JAMIE COURT, SUITE 302 3. Date of Earliest Transaction (MM/DD/YY) 09/13/2018 (Street) SOUTH SAN FRANCISCO, CA94080 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 3,945 D

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 Series A Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,070,771 I < /span> See Footnote ( 2 ) ( 3 ) Series B-1 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 312,741 I See Footnote ( 2 ) ( 3 ) Series B-2 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 260,617 I See Footnote ( 2 ) ( 3 ) Series B-3 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 544,047 I See Footnote ( 2 ) ( 3 ) Series C Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 167,537 I See Footnote ( 2 ) ( 3 ) Warrant to Purchase Series B-3 Preferred Stock $ 8.9931 ( 4 ) 12/29/2022 Series B-3 Preferred Stock ( 1 ) 28,623 I See Footnote ( 2 ) ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Thompson Peter A. C/O PRINCIPIA BIOPHARMA INC. 400 EAST JAMIE COURT, SUITE 302 SOUTH SAN FRANCISCO, CA94080 X Signatures Peter A. Thompson, by /s/ Ron Metzger, as attorney-in-fact 09/13/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of the issuer's Preferred Stock will automatically convert into 1 share of the issuer's Common Stock immediately upon the closing of the issuer's initial public offering and has no expiration date. ( 2 )These securities are held of record by OrbiMed Private Investments IV, LP ("OPI IV"). OrbiMed Capital GP IV LLC ("GP IV") is the sole general partner of OPI IV, and OrbiMed Advisors LLC ("Advisors") is the managing member of GP IV. By virtue of such relationships, GP IV and Advisors may be deemed to have voting and investment power over the securities held by OPI IV and as a result may be deemed to have beneficial ownership over such securities. The Reporting Person is an employee of Advisors. ( 3 )Each GP IV, Advisors and the Reporting Person disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its or his pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for the purpose of Section 16 of the Exchange Act, or for any other purpose. ( 4 )This warrant is exercisable at any time.

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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