The impact of the killer immunoglobulin-like receptor (KIR)-ligand mismatch between donor and recipient in hematopoietic stem cell transplantation is controversial. Recently, it has been suggested that their effect on cord blood transplantation (CBT) differs among types of mismatched KIR–ligand and graft-versus-host disease (GVHD) prophylaxis. To investigate their role in acute myeloid leukemia (AML), mismatch of KIR2DL1, KIR3DL1, and KIR3DL2-ligand (HLA-C2, Bw4, and A3/11) were retrospectively assessed in patients undergoing CBT with GVHD prophylaxis comprising a calcineurin inhibitor plus methotrexate (CNI/MTX) or mycophenolate mofetil (CNI/MMF). In patients who received CNI/MTX, a favorable effect of KIR-ligand mismatch on relapse was noted in HLA-C2 mismatched cases (24.8% at 3 years post-CBT [no HLA-C2 mismatch, n = 1602] vs. 15.4% [HLA-C2 mismatch, n = 161], P = 0.0116). In this group, overall survival (OS) was also superior (68.2%, P = 0.0083) compared to the other group (55.0%). Multivariate analysis results supported these findings (hazard ratio [HR] 0.61 for relapse, P = 0.017 and HR 0.72 for OS, P = 0.016). However, the KIR-ligand mismatch effect was not observed in patients with KIR-ligand mismatch types other than HLA-C2 and those using CNI/MMF for GVHD prophylaxis. These results suggest that HLA-C2 mismatch in CBT using CNI/MTX as GVHD prophylaxis may improve the outcomes of patients with AML.
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