 One of the complications of allogeneic stem cell transplant ASCT is graft versus host disease GVHD. This is when the donor cells that are infused attack the body organs. This can cause serious illness and even death. The chance of getting serious life threatening GVHD with conventional transplant conditioning regimens is 25-50 depending on whether the donor bone marrow is from a family member or an unrelated person. The reduced intensity conditioning regimen used in this study involves a drug called pentostatin as well as a reduced dose of radiation and a treatment called photopheresis. This regimen has been successfully used in 106 patients. The incidence of serious GVHD in those patients was much less than expected: 8 for patients getting bone marrow from a family member and 23 for those getting bone marrow from an unrelated person. The pentostatin and radiation parts of this reduced intensity conditioning regimen are similar to other types of reduced intensity regimens, which use drugs similar to pentostatin. The unique part of this regimen compared to others is the use of extracorporeal photopheresis ECP. 