Abstract

Emerging evidence has unveiled the contribution of tumor microenvironment to the regulation of chemotherapeutic outcomes. However, the impact of chemotherapy on anti-tumor immunity and immunosuppression still remains elusive. In this study, we investigated the role of chemotherapy-derived inflammatory responses in the differentiation of myeloid-derived suppressive cells (MDSC). The anti-cancer agents Gemcitabine and Carboplatin induced the activation of MAPK pathway in mouse mammary cancer cell line EO771 and also stimulated cytokine and chemokine production including GM-CSF and IL-6. The supernatants of Gemcitabine-treated tumor cells promoted more bone marrow-derived monocytic MDSC differentiation, and enhanced their immunosuppressive activity on effector T cells. The expression of MDSC associated molecules such as Arginase and iNOS significantly increased in M-MDSC induced by the supernatant of Gemcitabine-treated tumor cells. In vivo treatment of EO771 tumors with Gemcitabine increased the suppressive function of MDSC. Our findings also suggest that Dectin-1 activation by β-glucan could significantly reduce MDSC suppressive function. Together, these results describe a role of chemotherapy-derived inflammation in the modification of chemotherapy-treated tumor microenvironment and suggest the targeting of Dectin-1 signaling may benefit cancer patients by reprogramming MDSC in chemotherapy setting.