Natural Killer Cell Alloreactivity Predicted By Killer Cell Immunoglobulin-Like Receptor Ligand Mismatch Does Not Impact Engraftment in Umbilical Cord Blood and Haploidentical Stem Cell Transplantation

Natural killer cell alloreactivity is determined by killer cell immunoglobulin-like receptor (KIR) ligands in donor and recipient pairs. A small, single institution study suggested that the risk of primary graft failure after cord blood hematopoietic cell transplantation (CBT) can be predicted by host-versus-graft (HvG)-directed natural killer cell alloreactivity. In the haploidentical transplantation (Haplo HCT) cohort, graft failures were observed only in graft-versus-host (GvH) KIR ligand mismatched pairs. A subsequent study was designed to explore the association between HvG and GvH KIR ligand mismatching and engraftment in both CBT and Haplo HCT using the large, multicenter transplant population of the Center for International Blood and Transplant Research database. Nine hundred single CBT (sCBT), 954 double CBT (dCBT), and 671 Haplo HCT performed between 2008 and 2017 for acute leukemias and myelodysplastic syndrome were examined. Several models of KIR-L interactions were analyzed by multiple regression analyses for their association with engraftment, overall survival (OS), and transplant-related mortality (TRM). In sCBT, although HvG or bidirectional KIR ligand mismatch (KIR-L-MM) was initially associated with higher TRM in the first 6 months after transplantation, this effect was nullified after 6 months such that long-term survival was not different compared to GvH KIR-L-MM or KIR-L matched (KIR-L-M) pairs. There was no significant difference in neutrophil and platelet engraftment. In dCBT, no significant differences were seen in engraftment, OS and TRM. In the Haplo cohort there was faster platelet recovery in the GvH KIR-L-MM/KIR-L-M pairs versus HvG KIR-L-MM or bidirectional mismatch (HR 1.23, P= .0116). There was no significant association with OS, TRM, or neutrophil engraftment. In this large registry study, KIR-L mismatching did not significantly impact engraftment, TRM, or survival in CBT and Haplo HCT, although an association with platelet engraftment in Haplo HCT was demonstrated.