Human major histocompatibility complex (MHC) class I antigen-epitope peptide complex associated with β2-microglobulin are expressed by all human nucleated cells. It plays an important role in cell-mediated immune responses. Abnormalities in MHC class I antigen surface expression are frequently found in malignancies and infectious diseases. They are often associated with reduced recognition by MHC class I antigen-restricted, tumor or virus-associated antigen-specific cytotoxic T lymphocytes and disease progression. The EMR8-5 monoclonal antibody reacts with a non-polymorphic epitope of human MHC class I antigens, HLA-A, -B, and -C.