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HLA-A, B, and C are part of the Human Leukocyte Antigen （HLA） system, which is the human version of the Major Histocompatibility Complex （MHC）. HLA-A, B, and C are classic Class I molecules of the HLA system, expressed on the surface of all nucleated cells. They are responsible for presenting endogenous antigens, such as those produced by viruses or tumor cells, to CD8+ T cells, thereby activating cellular immune responses. These molecules consist of a heavy chain and a light chain （β2-microglobulin）, with the heavy chain encoded by the HLA-A, B, and C genes. In medical research, the expression of HLA-A, B, and C has been studied in various diseases, especially in tumor immunology. Research on HLA-A, B, and C also includes the frequency and clinical significance of their haplotypes in haplotype transplantation. Studying the frequency of these haplotypes is valuable for selecting the best donors and unrelated donors, particularly when performing related HLA haplotype transplantations.