Why Spero Therapeutics Stock Is Up 15% Today

Shares of small-cap biopharma company Spero Therapeutics (NASDAQ:SPRO) are up 15.3% as of midday Thursday after announcing a new product partnership with Pfizer (NYSE:PFE), in addition to a major equity investment by the same pharmaceutical icon. Namely, Pfizer is now a licensee of Spero's drug-resistant infection treatment SPR206, as well as an owner of about $40 million worth of Spero Therapeutics. That's nearly a 10th of the small company.