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Jibin Li, Jian Xu, Xiaofei Yan, Keer Jin, Wenya Li, Rui Zhang
(Department of Colorectal Surgery, Cancer Hospital of China Medical University (Liaoning Cancer Hospital and Institute), Shengyang, Liaoning, China (mainland))
Med Sci Monit 2018; 24:5501-5508
Limited efficacy of immune checkpoint blockades was observed in clinical trials in colorectal (CRC) patients, especially in the microsatellite-stable patients. Interleukin-6 (IL-6) is critical in modeling immune responses in cancers. However, the effects of targeting IL-6 in combination with immune checkpoint blockades is unknown in CRC.
MATERIAL AND METHODS: In the present study, we investigated the profile of IL-6 expression in tumor tissues of CRC patient and we established CRC mouse models with various IL-6 expression levels using CT26 cells and MC38 cells. Effects of anti-IL-6 and anti-PD-L1 combination treatment were tested in these models.
RESULTS: A total of 105 CRC patients were included in this study, with 41 (39%) females and 64 (61%) males. Sixty patients showed IL-6 high expression and 45 patients showed IL-6 low expression. The patients with IL-6 high expression tended to have shorter survival (median survival time of 25.5 months) than the patients with IL-6 low expression (median survival time of 46 months, P value=0.013). In the CRC mouse models, tumors with IL-6 overexpression tended to grow faster than the tumors with IL-6 knockout. The numbers of CD8+ T cells and CD4+ T cells were decreased in IL-6 overexpressed tumors. On the contrary, myeloid-derived suppressor cells and regulatory/suppressor T cells were more numerous in tumors with IL-6 overexpression. PD-L1 expression was upregulated in the tumors with IL-6 overexpression. Importantly, an IL-6 blockade reversed the anti-PD-L1 resistance and prolonged tumor-bearing mouse survival.
CONCLUSIONS: Our study indicates that IL-6 induces strong immunosuppression in the CRC microenvironment by recruiting immunosuppression cells and impairing T cell infiltration. Inhibition of IL-6 enhanced the efficacy of anti-PD-L1 in CRC, providing a novel strategy to overcome anti-PD-L1 resistance in CRC.