Busulfan, Fludarabine, and Total-Body Irradiation in Treating Patients Who Are Undergoing a Donor Stem Cell Transplant for Hematologic Cancer

RATIONALE: Giving low doses of chemotherapy, such as fludarabine and busulfan, before a donor peripheral blood stem cell transplant helps stop the growth of cancer cells. It also stops 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). Giving an infusion of the donor's T cells (donor lymphocyte infusion) after the transplant may help increase this effect. Sometimes the transplanted cells from a donor can also make an immune response against the body's normal cells. Giving cyclosporine and mycophenolate mofetil after the transplant may stop this from happening. PURPOSE: This phase I/II trial is studying the side effects of giving busulfan and fludarabine together with total-body irradiation and to see how well they work in treating patients who are undergoing a donor stem cell transplant for hematologic cancer.