Reduced-intensity conditioning by fludarabine/busulfan without additional irradiation or T-cell depletion leads to low non-relapse mortality in unrelated bone marrow transplantation

In reduced intensity, allogeneic stem cell transplantation from unrelated donors (u-RIST), graft-versus-host disease (GVHD), graft failure, and non-relapse mortality (NRM) are persistent problems. Although anti-thymocyte globulin, alemtuzumab, and total body irradiation (TBI) have been explored as conditioning modalities for u-RIST, the necessity for T-cell depletion or TBI to prevent GVHD or facilitate engraftment in u-RIST has not been determined. We here report the use of u-RIST with bone marrow grafting, following a simple conditioning regimen of 180 mg/m² fludarabine and 8 mg/kg of oral or intravenous busulfan without TBI or T-cell depletion. The study population was exclusively Japanese patients with a history of prior chemotherapy. We retrospectively analyzed 31 consecutive patients (median age 53 years). Twenty-five patients (81%) were transplanted from HLA-A, -B, and -DRB1 allele-matched donors. In all patients, neutrophil engraftment was achieved. The cumulative incidence of grade II–IV acute GVHD was 42%. However, 77% of patients with acute GVHD improved with, and could be managed by, initial, systemic, high-dose steroid treatment alone. Two-year overall and event-free survival was 62 and 53%, respectively. The NRM of 10% at 2 years was relatively low. Our results suggest that u-RIST without TBI or T-cell depletion may improve the prognosis after u-RIST in certain patient populations.