Pentostatin in Treating Patients With Refractory Chronic Graft-Versus-Host Disease

1. Histologic documentation of chronic GvHD following allogeneic HCT or donor lymphocyte infusion. 2. Patients may have progressive, quiescent, or de novo onset chronic GvHD. 3. Patients with extensive stage chronic GvHD requiring systemic immunosuppressive therapy are eligible. Patients with limited stage disease are excluded. Extensive stage is defined according to Seattle criteria (9) as either: * Generalized skin involvement or * Limited skin involvement or hepatic involvement with any one of the following: * Liver histology showing chronic progressive hepatitis, bridging necrosis or cirrhosis * Eye involvement (Schirmer's test with \< 5 mm wetting) * Involvement of minor salivary glands or oral mucosa * Involvement of any other organ 4. Patients must have failed treatment with, or experience progression after, prior corticosteroids for extensive stage chronic GvHD, as defined below. 4.1 Patients will be considered to have failed corticosteroids if they have any one of the following criteria: * Progressive disease or less than a minor response in any organ system despite 2 weeks on corticosteroid treatment at least 1 mg/kg methylprednisolone or equivalent. * Failure to achieve at least a minor response after at least 4 weeks of treatment with a dose of ≥ 0.5 mg/kg methylprednisolone or equivalent. * Achievement of less than a partial response at 8 weeks of corticosteroid treatment despite use of a dose ≥ 0.5 mg/kg methylprednisolone or equivalent. * Requirement of ≥ 0.5 mg/kg methylprednisolone or equivalent to maintain a partial response or better at 12 weeks of corticosteroid treatment. * Requirement of \> 10 mg/kg methylprednisolone or equivalent to maintain a partial response or better at 18 weeks of corticosteroid treatment. 4.2 Patients with progression of extensive stage chronic GvHD after a prior history of treatment with at least 18 weeks of corticosteroids, now requiring the reintroduction of corticosteroids (\> 10 mg/day methylprednisolone or equivalent) or an additional agent (including photopheresis, PUVA) for treatment. 5. Patients with established chronic GvHD not improving or progressing on other immunosuppressive agents are also eligible if steroid refractoriness has been established previously. 6. Age ≥ 18 years 7. Performance Status 0-3 8. Patients on mechanical ventilation are excluded. 9. No active infection. Patients with active infection requiring antibiotic therapy are not eligible until infection is controlled. 10. No HIV infection. Patients with HIV infection are excluded because of safety concerns in this patient population. 11. Non-pregnant and non-nursing. Women and men of reproductive potential should agree to use an appropriate method of birth control throughout their participation in this study due to the teratogenic potential of the therapy utilized in this trial (although it is unlikely that successful pregnancy will occur in patients with chronic GvHD). Appropriate methods of birth control include oral contraceptives, implantable hormonal contraceptives (Norplant®), or double barrier method (diaphragm plus condom). 12. Required Initial Laboratory Values: * Calc. Creatinine Clearance ≥ 30 mL/min/1.73 m\^2 * ANC \> 1000/μL * Platelets \> 50,000/μL without transfusion