Much of the success of hematopoietic stem cell transplantation (HSCT) has been due to the ability to overcome posttransplant complications, by performing HLA genotypically matched or even mismatched sibling donor HSCT or unrelated donor HSCT. Based on the promising results with using vigorously T-cell-depleted high-dose peripheral blood stem cell transplants by the Perugia University group, several methods to eradicate refractory leukemic cells have been employed worldwide. However, there are limitations of the existing data regarding haploidentical HSCT, that is, the small numbers of patients and the heterogeneous patient populations in most of the published series. Also, researchers have not exactly demonstrated the effect of natural killer (NK) cell alloreactivity in various settings of allogeneic HSCT. In reality, haploidentical HSCT is possible without T-cell depletion. However, it isn't clear whether reduced-intensity HSCT from a haploidentical related donor or a mismatched unrelated donor is feasible. Anyhow, successfully overcoming the major histocompatibility barriers with using related or unrelated donors means that virtually all patients would have an immediately available donor for desperately needed HSCT. The full potential of haploidentical HSCT may be ultimately achieved through a better understanding of the transplant immunology, including the Korean specificity of killer cell immunoglobulin-like receptor polymorphism. Further study and better support from Korean government insurance coverage that would offer HSCT to more patients in need of transplant and cultivating an optimal NK alloreaction without detrimental complications is urgently required.

Keywords: HLA mismatch, Haploidentical, Hematopoietic stem cell transplantation, Natural killer cell alloreactivity, Killer cell immunoglobulin-like receptor