Inclusion Criteria:

- Subjects must be 18 years to 70 years of age, inclusive

- Subjects must have received an allogeneic hematopoietic stem cell transplant using
either bone marrow, peripheral blood stem cells or cord blood or administered a donor
leukocyte infusion.

- Subjects must have newly diagnosed Grades B-D acute GVHD. Biopsy confirmation of GVHD
is strongly recommended but not required. Randomization should not be delayed
awaiting biopsy or pathology results.

- Subjects must be randomized and treated with corticosteroid (1-2 mg/kg/d
methylprednisolone, or equivalent) and Prochymal™/placebo within 72 hours of onset of
acute GVHD.

- Subjects must have adequate renal function as defined by: Calculated Creatinine
Clearance of >30mL/min using the Cockroft-Gault equation

- Subjects who are women of childbearing potential, must be non-pregnant, not
breast-feeding, and use adequate contraception. Male subjects must use adequate
contraception

- Subject must have a minimum Karnofsky Performance Level of at least 30 at the time of
study entry

- Subject (or legal representative where appropriate) must be capable of providing
written informed consent.

Exclusion Criteria:

- Subject has been previously treated with systemic immunosuppressive therapy for acute
GVHD

- Subject has any underlying or current medical or psychiatric condition that, in the
opinion of the Investigator, would interfere with the evaluation of the subject
including uncontrolled infection, heart failure, pulmonary hypertension, etc.

- Subjects may not receive any other investigational agents (not approved by the FDA
for any indication) concurrently during study participation or within 30 days of
randomization.

- Subject has a known allergy to bovine or porcine products or DMSO

- Subject has received a transplant for a solid tumor disease.

- Subject requires more than 2L/min of oxygen to maintain stable SaO2 greater than or
equal to 92%

- Subject requires a renal dopamine dose greater than 1-3 mcg/kg/min to maintain renal
blood flow associated with renal failure and improved urinary output.