Sec Form 4 Filing - BAKER BROS. ADVISORS LP @ Kiniksa Pharmaceuticals, Ltd. - 2018-02-09

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 BAKER BROS. ADVISORS LP 2. Issuer Name and Ticker or Trading Symbol Kiniksa Pharmaceuticals, Ltd. [ KNSA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 860 WASHINGTON STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 02/09/2018 (Street) NEW YORK, NY10014 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 Class A Common Shares 05/29/2018 P 299,403 A $ 18 299,403 I See Footnotes ( 1 ) ( 2 ) ( 14 ) ( 15 ) Class A Common Shares 05/29/2018 P 2,700,597 A $ 18 2,700,597 I See Footnotes ( 1 ) ( 3 ) ( 14 ) ( 15 )

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 C Preferred ( 5 ) 02/09/2018 P 420,897 ( 5 ) ( 5 ) Class A1 Common Shares 420,897 ( 4 ) 420,897 I See Footnotes ( 4 ) ( 6 ) ( 14 ) ( 15 ) Series C Preferred ( 5 ) 02/09/2018 P 3,734,103 ( 5 ) ( 5 ) Class A1 Common Shares 3,734,103 ( 4 ) 3,734,103 I See Footnotes ( 4 ) ( 7 ) ( 14 ) ( 15 ) Series C Preferred ( 5 ) 05/29/2018 C 420,897 ( 5 ) ( 5 ) Class A1 Common Shares 420,897 ( 13 ) 0 I See Footnotes ( 6 ) ( 8 ) ( 14 ) ( 15 ) Class A1 Common Shares ( 8 ) 05/29/2018 C 420,897 ( 8 ) ( 8 ) Class A Common Shares 420,897 ( 13 ) 420,897 I See Footnotes ( 6 ) ( 8 ) ( 14 ) ( 15 ) Series C Preferred ( 5 ) 05/29/2018 C 3,734,103 ( 5 ) ( 5 ) Class A1 Common Shares 3,734,103 ( 13 ) 0 I See Footnotes ( 7 ) ( 8 ) ( 14 ) ( 15 ) Class A1 Common Shares ( 8 ) 05/29/2018 C 3,734,103 ( 8 ) ( 8 ) Class A Common Shares 3,734,103 ( 13 ) 3,734,103 I See Footnotes ( 7 ) ( 8 ) ( 14 ) ( 15 ) Series B Preferred ( 9 ) 05/29/2018 C 313,621 ( 9 ) ( 9 ) Class A1 Common Shares 313,621 ( 13 ) 0 I See Footnotes ( 6 ) ( 10 ) ( 14 ) ( 15 ) Class A1 Common Shares ( 10 ) 05/29/2018 C 313,621 ( 10 ) ( 10 ) Class A Common Shares 313,621 ( 13 ) 734,518 I See Footnotes ( 6 ) ( 10 ) ( 14 ) ( 15 ) Series B Preferred ( 9 ) 05/29/2018 C 3,284,771 ( 9 ) ( 9 ) Class A1 Common Shares 3,284,771 ( 13 ) 0 I See Footnotes ( 7 ) ( 10 ) ( 14 ) ( 15 ) Class A1 Common Shares ( 10 ) 05/29/2018 C 3,284,771 ( 10 ) ( 10 ) Class A Common Shares 3,284,771 ( 13 ) 7,018,874 I See Footnotes ( 7 ) ( 10 ) ( 14 ) ( 15 ) Series A Preferred ( 11 ) 05/29/2018 C 1,399,516 ( 11 ) ( 11 ) Class B1 Common Shares 1,399,516 ( 13 ) 0 I See Footnotes ( 6 ) ( 12 ) ( 14 ) ( 15 ) Class B1 Common Shares ( 12 ) 05/29/2018 C 1,399,516 ( 12 ) ( 12 ) Class A Common Shares ( 12 ) 1,399,516 ( 13 ) 1,399,516 I See Footnotes ( 6 ) ( 12 ) ( 14 ) ( 15 ) Series A Preferred ( 11 ) 05/29/2018 C 14,658,102 ( 11 ) ( 11 ) Class B1 Common Shares 14,658,102 ( 13 ) 0 I See Footnotes ( 7 ) ( 12 ) ( 14 ) ( 15 ) Class B1 Common Shares ( 12 ) 05/29/2018 C 14,658,102 ( 12 ) ( 12 ) Class A Common Shares ( 12 ) 14,658,102 ( 13 ) 14,658,102 I See Footnotes ( 7 ) ( 12 ) ( 14 ) ( 15 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAKER BROS. ADVISORS LP 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY10014 X X 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY10014 X X Baker Brothers Life Sciences LP 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY10014 X X BAKER FELIX 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY10014 X X BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X Signatures By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 05/31/2018 Signature of Reporting Person Date Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to 667, L.P., pursuant to authority granted by Baker Biotech Capital, L.P., GP to 667, L.P. Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 05/31/2018 Signature of Reporting Person Date By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 05/31/2018 Signature of Reporting Person Date Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to BAKER BROTHERS LIFE SCIENCES, L.P., pursuant to authority granted by Baker Brothers Life Sciences Capital, L.P., GP to Baker Brothers Life Sciences, L.P., Name: Scott L. Lessing, Title: President /s/ 05/31/2018 Signature of Reporting Person Date /s/ Felix J. Baker 05/31/2018 Signature of Reporting Person Date /s/ Julian C. Baker 05/31/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds") purchased 299,403 and 2,700,597 Class A common shares of Kiniksa Pharmaceuticals, Ltd. (the "Issuer"), respectively, for $18.00 per share pursuant to the Issuer's initial public offering that closed on May 29, 2018. ( 2 )After giving effect to the transaction reported herein, and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in the Issuer's Class A common shares reported in column 5 of Table I that are directly held by 667, a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667. ( 3 )After giving effect to the transaction reported herein, and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in the Issuer's Class A common shares reported in column 5 of Table I that are directly held by Life Sciences, a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences. ( 4 )On February 9, 2018, 667 and Life Sciences purchased 420,897 and 3,734,103 Series C Convertible Preferred shares ("Series C Preferred") of the Issuer, adjusted for a 2.73235 for 1 reverse split on May 11, 2018, respectively, for $15.64 per share in a private financing. ( 5 )Series C Preferred will convert on a 1 for 1 basis (the "Series C Conversion Ratio") into Class A1 common shares of the Issuer as per the election of Baker Bros. Advisors LP (the "Adviser") at any time and automatically convert at the Series C Conversion Ratio upon the closing of the Issuer's initial public offering. The Series C Preferred have no expiration date. ( 6 )After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in securities reported in column 9 of Table II directly held by 667, a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667. ( 7 )After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in the Issuer's securities reported in column 9 of Table II directly held by Life Sciences, a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences. ( 8 )Represents conversion of the Issuer's Series C Preferred Shares into Class A1 common shares as per the election of the Adviser at the Series C Conversion Ratio upon the closing of the initial public offering of the Issuer. Class A1 common shares are, subject to a beneficial ownership limitation, convertible at any time at the election of the holder on a 1 for 1 basis into Class A common shares. The Class A1 common shares have no expiration date. Each Class A1 common share automatically converts into one Class A common share upon transfer, except for transfers to or between affiliated holders. ( 9 )Series B Convertible Preferred Shares of the Issuer ("Series B Preferred") convert into the Issuer's Class A1 common shares on a 1 for 1 basis (the "Series B Conversion Ratio") as per the election of the Adviser at any time and automatically convert at the Series B Conversion Ratio upon the closing of the Issuer's initial public offering. The Series B Preferred have no expiration date. ( 10 )Represents conversion of the Issuer's Series B Convertible Preferred shares into Class A1 common shares as per the election of the Adviser upon the closing of the initial public offering of the Issuer. Class A1 common shares are subject to a beneficial ownership limitation, convertible at any time at the election of the holder on a 1 for 1 basis into Class A common shares. The Class A1 common shares have no expiration date. Each Class A1 common share automatically converts into one Class A common share upon transfer, except for transfers to or between affiliated holders. ( 11 )Series A Convertible Preferred Shares of the Issuer ("Series A Preferred") convert on a 1 for 1 basis (the "Series A Conversion Ratio") into Class B1 common shares of the Issuer as per the election of the Adviser at anytime and automatically convert at the Series A Conversion Ratio upon the closing of the Issuer's initial public offering. The Series A Preferred have no expiration date. ( 12 )Represents conversion of the Issuer's Series A Preferred shares into Class B1 common shares as per the election of the Adviser at the Series A Conversion Ratio upon the closing of the initial public offering of the Issuer. Class B1 common shares are, subject to a beneficial ownership limitation, convertible at the election of the holder on a 1 for 1 basis into either Class B common shares or Class A common shares. The Class B1 common shares have no expiration date. Each Class B1 common share automatically converts into one Class A common share upon transfer, except for transfers to or between affiliated holders. ( 13 )Pursuant to Instruction 4(c)(iii), this response has been left blank. ( 14 )The Adviser serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviserreceives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds. The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. ( 15 )Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

Remarks: Felix J. Baker, a principal and Dr. Stephen R. Biggar, a full-time employee of Baker Bros. Advisors LP are directors of Kiniksa Pharmaceuticals, Ltd. (the "Issuer"). By virtue of theirrepresentation on the Board of Directors of the Issuer, for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the reporting persons are deemed directorsby deputization of the Issuer.

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