Mechanism of action of ICIs. The binding of PD-1/PD-L1 and CTLA-4/B7 receptor inhibit T cells response; the binding of MHC-TA and TCR activate T cell response. A: cancer cells reduce T cells response by up-regulating inhibition signals throughout the binding PD-1/PD-L1 and CTLA-4/B7 receptor. B: vice versa, the binding of ICIs to CTLA-4, PD-1 or PD-L1 prevent the activation of the anticancer pathway, by stimulating T cell response throughout MHC-TA/TCR binding.

APC: Antigen Presenting Cell; MHC: Major Histocompatibility Complex; TA: Tumor Antigen; TCR: T Cell Receptor.