Patients receive preparative cytoreductive therapy comprising total body irradiation on day -6; cyclophosphamide IV over 2 hours on days -5 to -2; fludarabine IV over 30 minutes on days -5 to -2; methylprednisone IV on days -5 to 24; anti-thymocyte globulin IV over 4-6 hours on days -5 to -1; cyclosporine IV over 2 hours every 12 hours (every 8 hours for patients less than 40 kg in weight) on days -3 to 180, and then tapering in the absence of graft-versus-host disease; hematopoietic cell transplantation on day 0; and filgrastim (G-CSF) IV starting on day 1 and continuing until blood counts recover.