HLA-mismatched Unrelated Donors Are a Viable Alternate Graft Source for Allogeneic Transplantation Following Alemtuzumab-based Reduced-intensity Conditioning

The impact of human leukocyte antigen (HLA) mismatch after reduced-intensity conditioning allogeneic hematopoietic stem cell transplantation (RIT) using unrelated donors (UD) is unclear, and may be modulated by T-cell depletion. We therefore examined outcomes of 157 consecutive patients undergoing RIT after uniform conditioning with fludarabine, melphalan, and alemtuzumab (FMC). Donors were 10/10 HLA-matched (MUDs, n = 107) and 6 to 9/10 HLA-matched (MMUDs, n = 50), with no significant differences in baseline characteristics other than increased cytomegalovirus seropositivity in MMUDs. Rates of durable engraftment were high. Graft failure rates (persistent cytopenias with donor chimerism) were similar (8% vs 3%, P = .21), though rejection (recipient chimerism) was more frequent in MMUDs (8% vs 0%, P < .01). There were no significant differences between donors in the incidences of acute graft-versus-host disease (GVHD; 20% vs 22% grade 2-4, respectively, P = .83), chronic extensive GVHD (3-year cumulative incidence [CI] 23% vs 24%, P = .56), or treatment-related mortality (1-year CI 27% vs 27%, P = .96). Furthermore, there was no difference in 3-year overall survival (OS; 53% vs 49%, P = .44). Mismatch occurred at the antigenic level in 40 cases. The outcome in these cases did not differ significantly from the rest of the cohort. We conclude that RIT using HLA-mismatched grafts is a viable option using FMC conditioning.