Prochymal Expanded Access Treatment for Pediatric Patients Who Have Failed Steroids for Acute GVHD

Inclusion criteria: * Patients must sign an informed consent form (ICF) before any protocol-related procedures, including any pre-treatment procedures, are performed. * Since patients being treated with Prochymal® under this protocol are under 18, a parental signature of informed consent will be required. * Patients must be 2 months to 17 years of age, inclusive. * Patients must have failed to respond to steroid treatment for Grades B-D acute GVHD • Failure to respond to steroid treatment for acute GVHD is defined as any Grade B-D acute GVHD that is not improving after at least 3 days of methylprednisolone (≥1 milligram per kilogram per day \[mg/kg/day\]) or equivalent. Exclusion criteria: * Patient must not have a known allergy to bovine or porcine products. * Patient must not have received a transplant for a solid tumor disease. * Patients must not have evidence of a pulmonary infiltrate or diffuse alveolar hemorrhage and must be unlikely to require more than 2 liters (L) of oxygen via face mask or an estimated fraction of inspired oxygen (FiO2) of 28% via other delivery methods in order to sustain an O2 saturation of 92% during the next 3 days.