HLA-A (Human Leukocyte Antigen A): HLA-A is a gene that encodes an MHC class I protein responsible for presenting peptide antigens to CD8⁺ T cells. It plays a key role in immune defense against pathogens and tumor cells. Variations in HLA-A can affect susceptibility to infections, autoimmune diseases, and transplant rejection, making it important in immune regulation and a potential target for immunotherapy.