13D Filing: Baker Bros. Advisors and Seattle Genetics Inc (SGEN)

(c) Except as disclosed herein or in any previous amendments
to this Schedule 13D, none of the Reporting Persons or their affiliates has effected any other transactions in securities of the
Issuer during the past 60 days.

 (d) Certain securities of the Issuer are held directly
by 667, a limited partnership the sole general partner of which is Baker Biotech Capital, L.P., a limited partnership the sole
general partner of which is Baker Biotech Capital (GP), LLC. Julian C. Baker and Felix J. Baker are the controlling members of
Baker Biotech Capital (GP), LLC.

Certain securities of the Issuer are held directly by Life Sciences,
a limited partnership the sole general partner of which is Baker Brothers Life Sciences Capital, L.P., a limited partnership the
sole general partner of which is Baker Brothers Life Sciences Capital (GP), LLC. Julian C. Baker and Felix J. Baker are the controlling
members of Baker Brothers Life Sciences Capital (GP), LLC.

(e) Not applicable.