Myeloid-derived suppressor cell accumulation in renal cell carcinoma is correlated with CCL2, IL-17 and IL-18 expression in blood and tumors

Background. Myeloid-derived suppressor cells (MDSC) play an important role in tumor-mediated immune evasion. Levels of MDSC in peripheral blood are increased in patients with cancer, correlating with cancer stage and outcome. Studies have confirmed the associations between MDSC and various cytokines in the peripheral blood of murine and human cancer hosts. However, little is known about the association between parenchymal MDSC subsets and cytokines, or the mechanism drawing MDSC into tumor parenchyma. Objectives. The aim of this study was to analyze the correlation between MSDSC subsets and tumor grade as well as stage in renal cell carcinoma (RCC) patients. The expression of chemokine (C-C motif) ligand 2 (CCL2), interleukin 17 (IL-17)and interleukin 18 (IL-18) in the peripheral blood and parenchyma of RCC patients was also detected to explore its correlation with MDSC accumulation. Material and methods. Total MDSC, granulocytic MDSC (G-MDSC), monocytic MDSC (M-MDSC), and immature MDSC (I-MDSC) from the blood and parenchyma were isolated and analyzed by flow cytometry. Cytokines were detected by the enzyme-linked immunosorbent assay (ELISA), real-time polymerase chain reaction (PCR) and western blot in blood and tumors. Results. Parenchymal levels of MDSC had a positive correlation with levels of CCL2, IL-17, and IL-18, suggesting these cytokines may attract MDSC into the parenchyma. Moreover, peripheral total MDSC, G-MDSC and I-MDSC were shown to correlate with tumor grade and stage. Gene and protein expression of CCL2, IL-17, and IL-18 was significantly increased in blood and tumors of RCC patients. Conclusions. Our study has provided potential new targets for the risk stratification of patients with limited stages of renal carcinoma, in addition to elucidating a possible association between MDSC subsets and cytokine-induced migration into the tumor tissue.