COLUMBIA, Md. ( TheStreet) -- Osiris Therapeutics ( OSIR) announced that its stem cell drug Prochymal failed both pivotal, phase III studies in patients with graft-versus-host-disease. The stock is currently halted with shares at $12.21. More details to follow. Update: The response rate data from the two Prochymal studies are horrible, despite Osiris' attempts a data-mining for something positive to say. In the study of patients with steroid-refractory GVHD, the Prochymal response rate was 35% compared to a 30% response rate for placebo – a result that wasn't statistically significant. The phase III study in first-line GVHD patients was even uglier, with Prochymal patients doing worse than placebo patients (a 45% response rate for Prochymal versus 46% response rate for placebo.) Osiris data mines the study for something positive to say, finding a couple of retrospective subsets of patients who seem to do better on Prochymal, but that's not going to matter. Bottom line: Prochymal failed, as I predicted long ago. Osiris shares are down 43% to $6.97 in pre-market trading.