Pentostatin, Cyclophosphamide Plus Rituximab (PCR) for the Therapy of Poor-Prognosis Chronic Graft-Versus-Host Disease

Inclusion Criteria: * Diagnosis of chronic GvHD requires at least one diagnostic and/or at least one distinctive manifestation. The latter must be confirmed by pertinent biopsy, laboratory tests, or radiology in the same or another organ. (See 19.11 details) * Confirmation of active chronic GvHD is desired but may not be feasible. * Age \>/= 18 yrs. No gender or ethnic restrictions. * Previously untreated chronic GvHD * Up to 15 days' of single agent therapy may be given for patients to be considered "previously-untreated", provided progression is not observed. * Vogelsang score20 \>/= 2 * If patients progress while on prednisone \>/= 0.5 mg/kg/day (or equivalent) for treatment of acute GvHD as they develop chronic GvHD, they may be considered candidates irrespective of the Vogelsang Score. * Prior therapy. Patients must have received prednisone \>/= 0.5 mg/kg/day plus one (or more) of the following second agents: tacrolimus, cyclosporine, sirolimus, or mycophenolate. * All second and subsequent failures are eligible. * Special circumstances: involvement of a "critical organ". In these cases, progressive involvement after the use of initial therapy will suffice as a eligibility criteria irrespective of the Vogelsang score. Exclusion Criteria: * Previous history of severe adverse reaction to either study agent. * Prior exposure alone to any of the agents in PCR is not a contraindication, Use of more than one of the agents in PCR to treat GvHD will exclude patients from entry. * Serious active infection (especially hepatitis B or C) not responding to therapy. * Active malignancy and/or the requirement of immunomodulation as treatment of malignancy. * Hematologic abnormalities: WBC \<3.0 K/uL, ANC \< 1.0 K/uL, Hgb \< 8.0 g/dL, platelets \< 50.0 K/uL. * Non-hematologic toxicities\*: * \*Renal. Measured creatinine clearance \<35 ml/min or the concomitant need for dialysis. * \*Pulmonary. DLCO \<40%, FEV1, 50%. * \*Hepatic. LFT (as measured by AST, ALT, T.bili) One or all of the levels found to be \>3 x normal. * Other. History of any significant co-morbid disease felt to make proposed therapy excessively risky. * Psychiatric. Patients with uncompensated severe psychiatric illness that would preclude signing the necessary consent forms or being compliant. * Compliance. Patients unlikely to adhere to study procedure and/or is unable or unwilling to return for necessary follow-up.