HLA-C and neoplasm: One study by Bai et al[128] has shown that adoptive therapy with both monoclonal and polyclonal transgenic cytotoxic T lymphocytes that are specific for the P1A tumor antigen selects for a number of mutations in the P1A antigenic epitope; consequently, by altering the interaction between major histocompatibility complex (MHC) and peptides, as well as T-cell receptor binding to the MHC:peptide complex, these alterations significantly reduced T-cell recognition of the tumor antigen; as a result, antigenic drift is one of the mechanisms through which tumor cells evade immune surveillance.