The major problem is presented by the immunosuppressive microenvironment created by the tumor, using various strategies such as low immunogenicity, high tumor burden (reviewed in [40]), secretion of immunosuppressive cytokines, low accessibility of CD8 T cells to the tumor (reviewed in [41]), the presence of regulatory T cells [42], accumulation of myeloid-derived suppressor cells (MDSCs) [43], tumor-associated macrophages (TAMs) [44], low MHC class I expression on cancer cells and T cell exhaustion (reviewed in [45]. The gene discussed is CD8A; the disease is cancer.