X0206 3 2017-11-01 0 0001701108 Spero Therapeutics, Inc. SPRO 0001378588 Deshpande Milind C/O SPERO THERAPEUTICS, INC. 675 MASSACHUSETTS AVENUE, 14TH FLOOR CAMBRIDGE MA 02139 1 0 0 0 Common Stock 16454 D Stock Option (Right to Buy) 5.90 2027-07-05 Common Stock 3290 D Stock Option (Right to Buy) 5.90 2027-07-05 Common Stock 45191 D The number of shares reported reflects a 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017. The shares underlying this option vested as to 25% on August 24, 2016, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date. The number of underlying shares of common stock and the exercise price reported reflect a 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017. The shares underlying this option vest as to 25% on July 6, 2018, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date. Exhibit 24.1 - Power of Attorney /s/ Matthew Tikonoff, Attorney-in-Fact for Milind Deshpande 2017-11-01