The major histocompatibility presented on the surface of the tumor cell complex (MHC) class I peptide complex induces the migration of CD8 tumor-infiltrating lymphocytes, helper T cells 1, CD4 T cells and macrophages into the tumor microenvironment to induce IFN-γ secretion for antitumor effects and to balance this active microenvironment, dMMR/MSI-H tumors selected for sustained upregulation of the T cell suppressor ligands PD-L1, CTLA-4, fostering immune escape. This evidence concerns the gene CTLA4 and neoplasm.