Significance of HLA 1-locus mismatch and ATG administration in unrelated hematopoietic stem cell transplantation

Abstract

HLA 1-locus-mismatched unrelated donors (1MMUD) are used in allogeneic hematopoietic stem cell transplantation (allo-HCT) for patients who lack an HLA-matched donor. Here we retrospectively reviewed 3,313 patients with acute leukemia or myelodysplastic syndrome who underwent bone marrow transplantation from an HLA allele-matched unrelated donor (MUD) or 1MMUD in 2009-2014. We compared the outcomes of MUD (n＝2,089) and 1MMUD with antithymocyte globulin [ATG; 1MM-ATG (＋) ; n＝109] with those of 1MMUD without ATG [1MM-ATG (-) ; n＝1,115]. In the 1MM-ATG (＋) group, the median total dose of ATG (thymoglobulin) was 2.5 (range, 1.0-11.0) mg/kg. The rates of grade III-IV acute GvHD, non-relapse mortality (NRM), and overall mortality were significantly lower in the MUD group than in the 1MM-ATG (-) group [hazard ratio (HR) 0.77; P＝0.016; HR, 0.74, P<0.001; and HR, 0.87, P＝0.020, respectively]. Similarly, the rates of grade III-IV acute GvHD, NRM, and overall mortality were significantly lower in the 1MM-ATG (＋) group than in the 1MM-ATG (-) group (HR, 0.42, P＝0.035; HR, 0.35, P<0.001; and HR, 0.71, P＝0.042, respectively). Even in the recent cohort, the outcome of allo-HCT from 1MM-ATG (-) was inferior to that of allo-HCT from MUD. Nevertheless, the negative impact of 1MMUD disappeared with the use of low-dose ATG without exacerbating the risk of relapse.