Protocol 265 was designed to evaluate Prochymal as a first-line agent for the treatment of acute GvHD in combination with steroid therapy. The majority of patients in this trial were suffering from skin GvHD, which responded significantly better to steroids than had been previously reported in controlled trials. This high response rate to standard of care diminished the potential for Prochymal to demonstrate an effect.

In the more severe, steroid-refractory GvHD setting (protocol 280), the benefit of adding Prochymal to second-line therapy was evaluated. Prochymal approached statistical significance for the primary endpoint in the per-protocol patient population which is the group of patients that met all of the study protocol requirements, such as inclusion and exclusion criteria. Additionally, Prochymal significantly improved response rates to liver and gastrointestinal GvHD, for which there is currently no known reliable therapy. Notably, the Prochymal cohort had more severe GvHD (27% of Prochymal patients had grade D GvHD, the most severe form, vs. 16% of placebo patients,>

Based upon the results of the steroid-refractory GvHD trial, Osiris plans to file an amendment with the FDA to the current expanded access program, broadening the entry criteria to include patients with severe GvHD of the liver.

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