For example, in the immunotherapy approaches using tumor peptide-specific CTL, dendritic cells (DCs), engineered CAR-T cells, tumor-infiltrating lymphocytes, or antibodies against PD-1, the target is the effector T cell, which kills MHC-positive, but not MHC-negative, tumor cells, resulting in recurrence of MHC-negative tumor cells (2). This evidence concerns the gene HLA-C and neoplasm.