Pancreatic cancer is an aggressive malignancy with 5 year survival rate of less than 5 percent. The predominant immune cells infiltrating the tumor microenvironment are monocytes/macrophages, which are reported to support tumor growth by suppressing host immune responses to the tumor. Recruitment of monocytes to various tissues, including tumors, is dependent upon activation of the chemokine receptor CCR2 by one or more of the chemokines CCL2, CCL8 and CCL13. In preclinical and clinical studies, inhibition of CCR2 in pancreatic cancer has shown to decrease tumor progression by blocking recruitment and accumulation of monocytes/macrophages in the tumor microenvironment. Analysis of the TCGA genomic database of human pancreatic tumors revealed elevation of both CCL2 and CSF1, which recruit monocytes, as well as the monocyte marker CD14, in advanced pancreatic cancers. Current immunotherapy using checkpoint inhibitors are effective in some tumors, but lack efficacy in immune insensitive cancers, including pancreatic cancer. Here, we report that the inhibition of CCR2 using small molecule antagonist potentiates anti-PD-1/PD-L1 immunotherapy in a syngeneic, orthotopic mouse model of pancreatic cancer. The KCKO pancreatic cancer cell line, which harbors a K-ras mutation, was implanted into the tail of the pancreas, and a small molecule CCR2 antagonist was administered after a stable tumor mass had formed. Tumor weight correlated well with the per cent of circulating monocytes in the peripheral blood, and the CCR2 antagonist significantly decreased the blood monocyte count. Similar to the human tumor stroma, the KCKO mouse tumors were infiltrated with monocytes and macrophages, and CCR2 antagonist treatment decreased the infiltration of monocyte/ macrophage. PD-L1 expressions are found in the human pancreatic tumor microenvironment, but treatment of patients with anti-PD-1 has not been found to have efficacy. Similarly, anti-PD-1 treatment alone was not effective in the murine KCKO model, but combination treatment with a CCR2 antagonist resulted in significantly smaller tumors. Moreover, this effect was completely reversed by depleting CD8 T cells, suggesting that by blocking monocyte/macrophage recruitment, the CCR2 antagonist relieved suppression of the CD8 T cells. We confirmed this hypothesis by demonstrating that cells from the KCKO tumor microenvironment inhibited CD3/CD28-induced proliferation of CD8 T cells in culture, but that this inhibition was not present when the mice had received the CCR2 antagonist. Taken together, these data reveal that blocking CCR2 decreases tumor burden by blocking monocyte infiltration and creating a microenvironment more favorable for CD8 T cells activity, and provide a mechanistic rationale for investigating the combination of a CCR2 antagonist and an immune checkpoint inhibitor in pancreatic cancer.

Citation Format: Heiyoun Jung, Linda Ertl, Christine Janson, Thomas Schall, Israel Charo. Inhibition of CCR2 potentiates the checkpoint inhibitor immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A107.