RATIONALE: Photopheresis treats the patient's blood with drugs and ultraviolet light outside the body and kills the white blood cells. Giving photopheresis, pentostatin, and radiation therapy before a donor bone marrow or stem cell transplant helps stop the patient's immune system from rejecting the donor's stem cells. The donated stem cells may replace the patient's immune system and help destroy any remaining cancer cells (graft-versus-tumor effect). Sometimes the transplanted cells from a donor can also make an immune response against the body's normal cells. Giving pentostatin before transplant and cyclosporine or mycophenolate mofetil after transplant may stop this from happening.