HUMAN LEUKOCYTE ANTIGEN POLYMORPHISM IN SEARCH FOR A MATCHED UNRELATED DONOR IN HAEMATOPOIETIC STEM CELL TRANSPLANTATION
The importance of recipient and donor matching for genes of the Human Leukocyte Antigens (HLA) system for the outcome of hematopoietic stem cell transplantation (HSCT) is well-established and documented. This review gives a brief summary of the genetic complexity of the HLA system, a description of HLA class I and II genes, as well as an overview of HLA class I and II molecules and their function in immunological processes. The review then focuses on the main characteristics of the HLA system that play an important role in HSCT, the extensive polymorphism of HLA genes and linkage disequilibrium, by providing examples of HLA alleles and haplotypes distribution in various worldwide populations. The second part of the review gives a detailed explanation of why the knowledge about this distribution is of great importance in the HSCT program, especially in the search for a matched unrelated donor (MUD), with respect to the evaluation of probabilities for finding a suitable donor. The final part of the review discusses the impact of different HLA mismatches on HSCT outcome in terms of the risk for graft vs. host disease (GvHD), transplant-related mortality, graft failure and overall survival.