Donor Stem Cell Transplant in Treating Patients With Relapsed Hematologic Cancer

RATIONALE: Giving low doses of chemotherapy, such as fludarabine and busulfan, before a donor bone marrow or 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 immunosuppressive therapy after the transplant may stop this from happening. PURPOSE: This phase II trial is studying how well donor bone marrow or peripheral stem cell transplant works in treating patients with relapsed hematologic cancer after treatment with chemotherapy and autologous stem cell transplant.