Spero Therapeutics, Inc. announced that it has entered into a securities purchase agreement with new investor Pfizer Inc. for private placement of 2,362,348 common shares $16.93 per share for gross proceeds of $39,994,551.64 on June 30, 2021. The company has raised funding as part of the Pfizer Breakthrough Growth Initiative. The company received funding from 1 investor pursuant to exemption provided under Regulation D.