This protocol allows for the treatment of pediatric patients, male and female, between the ages of 2 months and 17 years. Patients must have failed steroid treatment for Grade B-D acute GVHD.

For the treatment of pediatric patients who have failed to respond to steroid treatment for acute graft-versus-host disease (GVHD). Failing steroid treatment for acute GVHD is defined as any Grade B-D (IBMTR grading) of acute GVHD that is not improving after at least 3 days of methylprednisolone (≥ 1 mg/kg/day) or equivalent.

Patients will be treated with Prochymal twice per week at a dose of 2 x 10^6 hematopoietic stem cells (hMSC)/kg (actual body weight) for each of 4 consecutive weeks. Infusions will be administered at least 3 days apart.

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.