Aim of the work was to evaluate Pep R in potentiating the anti–PD-1 efficacy in two syngeneic murine models, the colon cancer MC38 cells [21–23] and the B16 melanoma model [22, 24] –human CXCR4 transduced, respectively reported to be immune responsive [21–23] and immune resistant cancer models [22, 24]. Here, CXCR4 is linked to malignant colon neoplasm.