Intratumoral Activity of the CXCR3 Chemokine System Is Required for the Efficacy of Anti-PD-1 Therapy

Despite compelling rates of durable clinical responses to programmed cell death-1 (PD-1) blockade, advances are needed to extend these benefits to resistant tumors. We found that tumor-bearing mice deficient in the chemokine receptor CXCR3 responded poorly to anti-PD-1 treatment. CXCR3 and its ligand CXCL9 were critical for a productive CD8+ T cell response in tumor-bearing mice treated with anti-PD-1 but were not required for the infiltration of CD8+ T cells into tumors. The anti-PD-1-induced anti-tumor response was facilitated by CXCL9 production from intratumoral CD103+ dendritic cells, suggesting that CXCR3 facilitates dendritic cell-T cell interactions within the tumor microenvironment. CXCR3 ligands in murine tumors and in plasma of melanoma patients were an indicator of clinical response to anti-PD-1, and their induction in non-responsive murine tumors promoted responsiveness to anti-PD-1. Our data suggest that the CXCR3 chemokine system is a biomarker for sensitivity to PD-1 blockade and that augmenting the intratumoral function of this chemokine system could improve clinical outcomes. [Display omitted] •Anti-PD-1 efficacy depends on intratumoral activity of the CXCR3 chemokine system•CD103+ dendritic-cell-derived CXCL9 and CXCR3 on CD8+ T cells are required•CXCR3 ligands are positive indicators of responsiveness to anti-PD-1 therapy•Inducing CXCR3 ligands in non-responsive tumors restores sensitivity to anti-PD-1 Chow et al. find the CXCR3 chemokine system is not required for CD8+ T cell migration into the tumor, but rather for the enhancement of the intratumoral CD8+ T cell response in the context of PD-1 blockade. The CXCR3 chemokine system might serve as a biomarker for sensitivity to PD-1 blockade and a target for improving clinical outcomes.