Recipient preparation: The development of aggressive preparative regimens has improved outcome by reducing the incidence of rejection and relapse. These regimens have increased antitumor or antileukemic potential as well as delivered superior myeloablation, necessary to destroy the host marrow and make room for the donor graft without compromising the marrow stromal elements essential for engraftment. Preparative regimens also suppress the patient's immune system to allow for acceptance of the graft.

Patients are given high dosages of cyclophosphamide and/or total body irradiation in standard preparation regimens. The rejection rate is < 5% in transplants for leukemia patients from HLA-identical donors. For multiply transfused patients with aplastic anemia, the rejection rate has also been significantly decreased because of increased immunosuppression during transplant induction. The two most common preparative regimens are high-dosage cyclophosphamide (eg, 60 mg/kg/day for 2 days) and total body irradiation or a regimen of busulfan (eg, 4 mg/kg/day for 4 days) and cyclophosphamide without total body irradiation. Other drugs (eg, etoposide and cytarabine) are sometimes added to these transplant regimens to maximize antitumor properties, myeloablation, and immunosuppression.