Under pathological conditions, CTLA-4 and PD-1, which are expressed on activated T lymphocytes, bind to the corresponding ligand B7 molecule on APCs and PD-L1 expressed on the tumor cells, contributing to an inhibitory immune signal that refines the activity of T cells and assists tumors in evading immunosurveillance.445,446. Here, CTLA4 is linked to neoplasm.