The Influence of KIR Gene Polymorphisms and KIR-ligand Binding on Outcomes in Hematologic Malignancies following Haploidentical Stem Cell Transplantation: A Comprehensive Review

Natural killer (NK) cell behavior and function are controlled by a balance between negative or positive signals generated by an extensive array of activating and inhibiting receptors, including killer cell immunoglobulin-like receptor (KIR) proteins, main components of the innate immune system that contribute to initial responses against viral infected-transformed cells through generation of the release of cytokines and cytotoxicity. What is certain is that KIRs are genetically polymorphic and the extent of KIRs diversity within the individuals may have the potential outcomes for hematopoietic stem cell transplantation (HSCT). In this regard, recent studies suggest that KIR is as imperative as its ligand (HLA) in stem cell transplantation for malignant diseases. However, unlike HLA epitope mismatches, which are well-known causes of NK alloreactivity, a complete understanding of KIR genes' role in HSCT remains unclear. Because of genetic variability in KIR gene content, allelic polymorphism, and cell-surface expression among individuals, an appropriate selection of donors based on HLA and KIR profiles is crucial to improve outcomes of stem cell transplantation. In addition, the impact of the KIR/HLA interaction on HSCT outcomes needs to be investigated more comprehensively. The present work aimed to review the NK cell regeneration, KIR gene polymorphisms, and KIR-ligand binding on outcomes in hematologic malignancies following haploidentical stem cell transplantation. Comprehensive data gathered from the literature can provide new insight into the significance of KIR matching status in transplantations.