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Abstract 4999: Characterization of myeloid derived suppressor cells after capecitabine and nivolumab combination treatment

Capecitabine, a widely used oral chemotherapeutic agent, only functions in its active form, 5-FU. The metabolism of capecitabine to 5-FU frequently occurs in tumor tissues with high expression of thymidine phosphorylase, enzyme responsible for converting capecitabine. Extensive studies have demonstrated that capecitabine functions to inhibit growth of tumors, especially for metastatic breast and colorectal tumors, by impairing DNA synthesis and metabolism. However, effects of capecitabine on myeloid derived suppressor cell (MDSC) in the tumor microenvironment are poorly understood. In fact, conflicting results were reported that capecitabine either reduced CD11b high /Gr1 high MDSC and enhanced T cell functions, or failed to alter the number and function of MDSC or the levels of GM-CSF/IL6 in blood. In this study, we established an optimized in-vitro MDSC suppressive assay and take the advantage of this system to investigate the function of capecitabine on MDSC-mediated T cell suppression. Myeloid cells in tumor environment acquire the expression of PD-L1, suggesting that blocking the PD1-PD-L1 axis might revert the function of MDSC. Therefore, we further explored the combination effect of capecitabine and nivolumab, a PD-1 antibody, on the function of MDSC in human PBMC cells. Citation Format: Qing Lin, Tienan Wang, Wenjun Yan, Ranran Wu, Lun Nie, Chensi Miao, Xing Wang, Feng Wang, Jie Zhang, Weilin Shi, Yanping Yuan, Tingting Shi, Ao Li, Wei Dong, Xu Chen, Jingying Sun, Qunsheng Ji. Characterization of myeloid derived suppressor cells after capecitabine and nivolumab combination treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4999.