Natural killer (NK) cells were identified over 30 years ago by their ability to kill cancer and virally infected cells without prior sensitization. For years the recognition mechanisms of target cells were unknown, until the 1990s when the "missing-self" hypothesis was proposed. According to this theory, although tolerant to normal autologous cells, NK cells can recognize and attack cells that have down-regulated human leukocyte antigen (HLA) class I molecules. The discovery of killer immunoglobulin-like receptors (KIR) that specifically recognize HLA class I molecules corroborated this hypothesis. These new concepts point to the importance of studying KIR in hematopoietic stem cell transplantation (HSCT). HLA disparities between the donor and patient in HSCT may be distinguished by NK cells leading to alloreactivity. Even though there are some promising results, until now existing studies have not reached any consensus. Here, we will review the relevance of NK cells and KIR in the different types of HSC.
KIR; NK cells; hematopoietic stem cell transplantation; leukemia
