Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	Owned after	D/I
Class A1 Common Shares^{F2,F1,F4,F5,F6,F3}	—	Feb 4, 2019	A	181,525	A	—	—	Class A Common Shares	181,525	916,043	I
Class A1 Common Shares^{F2,F1,F4,F5,F7,F3}	—	Feb 4, 2019	A	1,818,475	A	—	—	Class A Common Shares	1,818,475	8,837,349	I

Explanation of responses

F1667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences" and together with 667, the "Funds") purchased 181,525 and 1,818,475 Class A common shares of Kiniksa Pharmaceuticals, Ltd. (the "Issuer"), respectively, for $18.26 per share pursuant to a private placement with the Issuer that closed on February 4, 2019.
F2Pursuant to Instruction 4(c)(iii), this response has been left blank.
F3Represents the Issuer's Class A1 common shares which are subject to a beneficial ownership limitation, convertible 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.
F4Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives 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.
F5Julian 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.
F6After 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.
F7After 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.

Remarks

Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC 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 their representation 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 directors by deputization of the Issuer.