Cisplatin inhibits the progression of bladder cancer by selectively depleting G-MDSCs: A novel chemoimmunomodulating strategy.

Bladder cancer (BC) is a disease arising from the malignant cells of the urinary bladder. Myeloid-derived suppressor cells (MDSCs) expand broadly and have strong immunosuppressive activities in the cancer microenvironment. Determining how to inhibit the negative effects of MDSCs requires immediate attention. In this study, we found that granulocytic-MDSCs (G-MDSCs), which constitute one of the two types of MDSCs, were significantly increased in BC tissues compared with those in the adjacent bladder tissues. There was a robust negative correlation between the G-MDSCs and the CD8+ T cells in the BC tissues. In this study, we attempted to identify pharmacological approaches to eliminate MDSCs and restore T cell anti-tumor activities. It is necessary to explore a method to eliminate the detrimental effects of MDSCs. Cisplatin, a chemotherapy medication used to treat BC, not only rapidly kills proliferating cancer cells but also affects the tumor immune microenvironment. However, the mechanism underlying this phenomenon is largely unknown. In this study, we found that Cisplatin directly inhibited the proliferation and induced the apoptosis of T24 cells (a BC cell line), as well as decreased the percentage of the G-MDSCs in the population of peripheral blood mononuclear cells (PBMCs), which restored the expansion of the CD8+ T cells. In the C3H/He mouse BC model, Cisplatin treatment inhibited the progression of BC and effectively decreased the proportion of G-MDSCs. These results suggest that Cisplatin treatment enhances the anti-tumor function of CD8+ T cells by decreasing G-MDSCs. This finding provides a new perspective for Cisplatin treatment to prevent the progression of BC, particularly in patients with abnormally high levels of G-MDSCs.