In the process of antitumor immune response in normal organisms, antigen-presenting cells present tumor-specific antigen (TSA) as major histocompatibility complex (MHC) and bind to T cell surface TCR (T cell receptor) and then, under the action of various costimulatory signal molecules, activate T cells; activated T cells, mainly cytotoxic CD8+ T cells, bind to tumor cells via recognition of TSA on their surface and kill tumor cells after the costimulatory signal is activated [21, 22]. The gene discussed is CD8A; the disease is neoplasm.