CTLA4 and neoplasm: This phase may be blocked when the immunosuppressive cytokines produced by the tumor cells or by the immunosuppressive lymphocytes (T-reg) recruited by the tumor cells, induce the expression of the Cytotoxic-T-Lymphocytes Associated antigen-4 (CTLA-4) rather than the costimulatory receptor CD28, on the cell membrane of cytotoxic T-lymphocytes.