HLA in Hematopoietic Stem Cell Transplantation

Abstract

The successful outcome of hematopoietic stem cell transplantation (HSCT) depends on the extent of HLA (human leukocyte antigen) matching between the patient and their prospective donors. Human leukocyte antigen are proteins which are expressed on the immune cells on the body and are responsible for presenting the processed foreign peptides to the cells for further processing by the immune system. The recognition of alloantigen resulting from HLA disparity between the patient-donor pair results in detrimental effects in the form of graft versus host disease (GVHD) or graft rejection, reducing the performance of allogenic HSCT. Thus, the ideal donor for such transplantation is a HLA genotypically identical sibling donor. Unfortunately, only 30% of the patients have the HLA identical donor and are left with the matched unrelated donors (MUD), haploidentical donors, and cord blood available for the transplant. Transplant using such alternate donors have been faced with dismal consequences in the beginning, but with the subsequent advancement in the treatment protocol, have gradually proved to be a promising possibility. The selection of an alternative donor for a successful transplant requires a thorough understanding of the highly polymorphic HLA system. There has been an extensive development in the field of histocompatibility testing which is able to give us entire sequence information about a particular HLA locus. With the expanding use of haploidentical donors as an alternative donor source, the role of HLA antibody directed against mismatched donor HLA has become important. It has been observed in many instances that these donor-specific antibodies (DSA) have been directly responsible for primary graft rejection. The analysis of DSA is now highly recommended in haploidentical transplant setting. The relevance of the killer immunoglobulin receptor (KIR) typing has been explored which may give us the information to choose the most appropriate donor amongst a number of available haploidentical donors. Thus, a better understanding of the HLA system is a prerequisite and critical for choosing the best suitable donor which will be most effective for patients undergoing HSCT.