To determine a safe and effective dose of pentostatin in steroid-refractory aGvHD and to identify the minimal effective dose of pentostatin defined as the lowest dose that produces a response in 20% or more of patients while producing treatment failure (defines as death, grade 3/4 toxicity, or progressive disease) in 40% or less of patients.

Inclusion:

• Patients 6 months of age with grade 2 GVHD that is steroid-refractory
• Must be engrafted with ANC 1000/mL, may still be transfusion dependent for platelets and PRBC
• Time post stem cell infusion < 100 days
• Written informed consent
• Must have adequate renal function (creatinine clearance 40 mL/min/1.73 m2)

Exclusion:

• Post-transplant lymphoproliferative disease
• Uncontrolled infection
• Mental illness or other condition preventing full cooperation with the treatment and monitoring requirements of the study
• ATG within the previous 14 days
• Other immunosuppressive agents (including monoclonal antibodies) when initiated within the previous 7 days