The purpose of this protocol remains a pilot study which is now regarded as a phase II trial with a plan to enroll 40 ADDITIONAL patients (20 related and 20 unrelated donor transplants) with hematological malignancy assessing the safety and efficacy of a modified version of the original preparative regimen of Pentostatin and low-dose total body irradiation (TBI) followed by allogeneic peripheral blood stem cell transplantation (alloPSCT). Patients who fail will become candidates for donor-leukocyte infusion (DLI).