CTLA4 and neoplasm: Of these, two immunosuppressive pathways have gained great interest as they can be therapeutically targeted: the pathway of cytotoxic T lymphocyte antigen 4 (CTLA4), a molecule expressed by T cells inhibiting their function, and the programmed cell death 1 ligand 1 (PD-L1 or B7H1) pathway used by tumor cells to inhibit the antitumoral immune response.