CTLA4 and neoplasm: Then, the strongly activated immune cells provoke the expression of immune-checkpoint receptors and ligands, such as cell surface protein programmed death-1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA4), and transmembrane protein programmed death-ligand 1(PD-L1) on tumor cells, TILs, regulatory T (Treg) cells and tumor-associated macrophages.