A Well-Tolerated Regimen of 800 cGy TBI-Fludarabine-Busulfan-ATG for Reliable Engraftment after Unmanipulated Haploidentical Peripheral Blood Stem Cell Transplantation in Adult Patients with Acute Myeloid Leukemia

Eighty adult patients with acute myeloid leukemia (AML) received peripheral blood T cell-replete HLA haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Disease status at transplantation was either first or second complete remission (CR, n= 69) or relapse/refractory (n= 11). Identical transplant-related procedures with conditioning regimen consisting of fractionated 800 cGy total body irradiation (TBI), fludarabine (30 mg/m²/day for 5 days), busulfan (3.2 mg/kg/day for 2 days), and antithymocyte globulin (1.25 mg/kg/day on days-4 to-1) and graft-versus-host disease (GVHD) prophylaxis with tacrolimus and methotrexate were used in all patients. Recovery of neutrophil (median, 11 days) and platelet (median, 10 days) counts was achieved in all patients with full donor chimerism (≥99%), and no delayed engraftment failure was observed. The cumulative incidence of grades III to IV acute GVHD and moderate to severe chronic GVHD was 11.2% and 26.3%, respectively. A donor CD8⁺ and CD4⁺ T cell dose above the median value was significantly associated with the incidences of grades II to IV acute GHVD and moderate to severe chronic GVHD, respectively. After a median follow-up of 28 months for survivors, the 2-year cumulative incidences of relapse (n= 20) and nonrelapse mortality (n= 10) were 26.6% and 12.2%, respectively. Although all but 1 patient in relapse/refractory status died, the 2-year overall and progression-free survival of patients in first CR was 82.5% and 75.1%, respectively. We suggest the strategy of fractionated 800 cGy TBI-based conditioning with unmanipulated peripheral blood stem cell grafts seems feasible with favorable outcomes for adult patients with AML undergoing haplo-HSCT in CR.