CTLA4 and neoplasm: Briefly, a wide set of processes make the tumor invisible to the immune system: (i) shedding of antigens and losing MHC on tumor cells; (ii) downregulation of adaptive and innate immune responses by secretion of cytokines (TGF-β, IL-10); (iii) induction of CTLA-4 (cytotoxic T lymphocyte associated antigen-4) or regulatory T cells [27,28]; (iv) production of myeloid suppressor cells (MSCs) with immune suppressive function; (v) expression of aberrant antigens on tumor cells (e.g., HLA-G); (vi) resistance to apoptosis and vascularization by VEGF.