CTLA4 and neoplasm: PD-L1 (the ligand of PD-1) is mainly expressed on tumor cells and tumor-infiltrating immune cells, and it functions to inhibit T-cell activity by binding to PD-1.219,220 The action of PD-1/PD-L1 inhibitors is to block the binding between PD-1 and PD-L1, restoring the immune cells’ ability to recognize and kill tumor cells.221 CTLA-4 inhibitors work by blocking the binding of CTLA-4 to the B7 molecules (B7-1 and B7-2) on the surface of antigen-presenting cells, thereby relieving the inhibitory state of T cells.