PD-1 is expressed on activated immune cells and can link to PD-L1 express on Antigen-Presenting-Cell. Usually, this pathway is involved in promoting T-cells tolerance and preventing tissue damage in settings of chronic inflammation. In pathological context, the PD-1/PD-L1 pathway contributes to immune suppression and evasion. Many human solid tumors including colo-rectal cancer express PD-L1, and this expression is associated with a worse prognosis. The interaction of PD-1 with the ligand PD-L1 inhibits T-cell proliferation, survival, and effectors functions; induces apoptosis of tumor-specific T cells; promotes the differentiation of CD4+ T cells into immunosuppressive regulatory T cells; and increases the resistance of tumor cells to cytotoxic T lymphocytes attack. Thus, the blockage of the PD-1/PD-L1 interactions represents a logical target for cancer immunotherapy and in particular colo rectal cancer immunotherapy strategy.