GRAFT-VERSUS-HOST DISEASE (GVHD) PROPHYLAXIS: Patients receive tacrolimus orally (PO) or IV twice daily (BID) on days -2 with taper between days 90-120, and stopping by days 150-180. Patients also receive methotrexate IV on days 1, 3, 6, and 11 and rabbit antithymocyte globulin IV over 4-6 hours on days -4 through -2.