A REVIEW ON MAJOR HISTOCOMPATIBILITY: IMPLICATIONS IN TRANSPLANTATION AND GRAFT REJECTION

The Major Histocompatibility Complex (MHC), which can also be known as the Human Leukocyte Antigen (HLA) system in humans, is one of the significant elements in transplantation immunobiology due to their role in antigen presentation and immunity tolerance. Polymorphism in particular is one of the main characteristics of MHC that determines its role in donor-recipient matching, affecting the outcome of the transplantation process, which includes both solid organ transplantation and HSCT procedures. In regard to solid organ transplantation, for example, during kidney transplantation procedure, HLA incompatibility is a source of alloreactivity in the recipient’s immune system via either the direct, indirect, and semi-direct pathways leading to the rejection of transplanted organs in an acute and chronic manner. Another form of rejection that is mediated by antibody response to donor HLAs, as well as other antigens like MICA, is strongly related to the development of DSAs, particularly in case of prior sensitization. HLA compatibility is critical for successful transplantation in HSCT in order to avoid Graft-versus-host Disease (GVHD), where even small degrees of disparity may affect the outcome. Progress made in developing more accurate approaches, such as high resolution typing and epitope-matching, has played a critical role in enhancing the compatibility between patients and donors. Prospective approaches, which include Treg cell therapy, immune tolerance induction, and gene editing, among others, show great promise in this respect, although their effectiveness is yet to be confirmed by experiments/clinical trials. Finally, advanced diagnostic tools, including crossmatch, PRA, and DSAs, have proven highly valuable in identifying possible dangers. In conclusion, this paper summarizes the existing knowledge concerning MHC in terms of its involvement in transplantation from molecular, immunological, and clinical perspectives.