Sanofi is handing back full rights to KB001-A, a monoclonal antibody from KaloBios that targets Pseudomonas aeruginosa (Pa), a bacterium implicated in pneumonia and lung infections tied to cystic fibrosis.

KaloBios isn’t saying what led Sanofi to abandon the treatment, which is in the midst of a Phase II study, but the company wasted no time in pointing out that it is free to find another partner and will immediately embark on a search to do so.

The biotech is plowing ahead with its Phase II program, recently wrapping enrollment on a planned 180-patient study designed to test KB001-A’s benefits in cystic fibrosis sufferers with Pa-related lung infections. The plan is to release top-line data from that study in 2015.