Colorectal cancer and immunity: What we know and perspectives

Figure 1 Major mechanisms of tumor immune escape. Tumor cells can induce immunosuppression by different pathways: (1) tumor cells can secrete immunosuppressive cytokines as vascular endothelial growth factor (VEGF), interleukin-10 (IL-10) or transforming growth factor-β (TGFβ). These molecules contribute to blockade of maturation of dendritic cells (DC) and then induce regulatory T cells (Treg) rather than lymphocytes T (LT) CD4⁺ or CD8⁺ cells. VEGF could promote directly induction and proliferation of Treg; (2) Tumor cells down-regulate expression of CMH-1; (3) Tumor cell express inhibitory molecules as PDL1 or CD80, and induce exhaustion of LT; and (4) Tumor cells can evade apoptosis by inducing anti-apoptotic molecules such as C-FLIP, or by down-regulating the expression of death receptors such as FAS.