CTLA4 and neoplasm: A key mechanism in tumorigenesis is an immune response to the tumor, illustrated by the effectiveness of immune checkpoint inhibitors (ICIs) acting against, for example, PD-1, PD-L1, and CTLA-4 (32), because of the evidence that blockade of PD-1 and PD-L1 is an extremely promising approach in cancer immunotherapy for preventing tumor evasion of host tumor antigen-specific T-cell immunity.