Interactions between interleukin-6 and myeloid-derived suppressor cells drive the chemoresistant phenotype of hepatocellular cancer.

Emerging evidence implicates an important role for myeloid-derived suppressor cells (MDSCs) in tumor growth, angiogenesis and metastasis. However, limited knowledge is known about the function of MDSCs in response to chemotherapies. In this study, we find that drug-resistant hepatocellular cancer (HCC) cells-derived conditioned medium significantly enhances the expansion and immunosuppressive function of MDSCs compared to their parental sensitive cells, which is demonstrated by increased level of arginase, nitric oxide (NO), and reactive oxygen species (ROS). Next, we reveal that drug-resistant HCC cells-derived IL-6 activated MDSCs, which is demonstrated by using an anti-IL-6 neutralizing antibody that caused a reduced MDSC immunosuppressive activity. More importantly, the depletion of MDSC via the administration of anti-Gr-1 antibody or the blockade of IL-6 signaling sensitized 5-FU-resistant H22 hepatoma to chemotherapy in the immunocompetent C57BL/6N mice. In primary human HCC, IL-6 expression levels strongly correlate with an MDSC phenotype and chemotherapy response in HCC patients. In conclusion, these results describe a role of IL-6 in the drug resistance in HCC chemotherapy and suggest that MDSC-targeting treatments may be potential therapeutic strategy for HCC chemoresistance.