Efficacy and Safety of Prochymal® Infusion in Combination With Corticosteroids for the Treatment of Newly Diagnosed Acute Graft Versus Host Disease (GVHD)

Participants will be treated with a total of 6 infusions of investigational agent during the first 4 weeks of the study. The first infusion of the investigational product (IP) will be administered within 72 hours of the start of systemic corticosteroid therapy. Four infusions will be administered during the first two weeks (twice weekly), then two infusions administered during the next two weeks (once weekly). Participants assigned to the active treatment group will receive Prochymal®. Participants assigned to the non active treatment group will receive placebo (excipient, less cells). It is recommended that all participants receive all six infusions. The discontinuation of investigational agent is allowed for GVHD worsening with subsequent need for salvage therapy. All infusions must be given at least 3 days apart. Participants will be evaluated for efficacy and safety until death, withdrawal or 90 study days after randomization, whichever occurs first. Study will be unblinded and data analyzed at Day 90 post 1st infusion (Day 0) following final participant enrollment. Participants will be followed for safety for 12 months post 1st infusion (Day 0).