Spero Therapeutics, Inc. — Director's Dealing 2017

Nov 7, 2017

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: Spero Therapeutics, Inc. (SPRO)
CIK: 0001701108
Period of Report: 2017-11-06

Reporting Person: GLAXOSMITHKLINE PLC (10% Owner)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2017-11-06	Common Stock	C	244147	—	Acquired	244147	Indirect
2017-11-06	Common Stock	C	246272	—	Acquired	490419	Indirect
2017-11-06	Common Stock	C	328992	—	Acquired	819411	Indirect
2017-11-06	Common Stock	C	606024	—	Acquired	1425435	Indirect
2017-11-06	Common Stock	P	428571	$14	Acquired	1854006	Indirect

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2017-11-06	Junior preferred stock	$	C	1483784	Disposed		Common Stock (244147)	Indirect
2017-11-06	Series A preferred stock	$	C	982906	Disposed		Common Stock (246272)	Indirect
2017-11-06	Series B preferred stock	$	C	1250000	Disposed		Common Stock (328992)	Indirect
2017-11-06	Series C preferred stock	$	C	3683045	Disposed		Common Stock (606024)	Indirect

Footnotes

F1: S.R. One, Limited acquired 428,571 common shares of the Issuer in connection with the Issuer's initial public offering.

F2: Amount of underlying securities reflects the application of the applicable conversion ratio as set forth in the Issuer's Amended and Restated Certificate of Incorporation in effect immediately prior to the closing of the initial public offering (as adjusted by the 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017). The preferred stock had no expiration date.

F3: The shares reported herein are held of record by S.R. One, Limited, an indirect,wholly-owned subsidiary of GlaxoSmithKline plc (the "Reporting Person").