Interleukin-17A facilitates tumor progression via upregulating programmed death ligand-1 expression in hepatocellular carcinoma.

Background: Hepatocellular carcinoma (HCC) is an inflammation-associated tumor with a dismal prognosis. Immunotherapy has become an important treatment strategy for HCC, as immunity is closely related to inflammation in the tumor microenvironment. Inflammation regulates the expression of programmed death ligand-1 (PD-L1) in the immunosuppressive tumor microenvironment and affects immunotherapy efficacy. Interleukin-17A (IL-17A) is involved in the remodeling of the tumor microenvironment and plays a protumor or antitumor role in different tumors. We hypothesized that IL-17A participates in tumor progression by affecting the level of immune checkpoint molecules in HCC.

Aim: To investigate the effect and mechanism of action of IL-17A on PD-L1 expression and to identify attractive candidates for the treatment of HCC.

Methods: The upregulation of PD-L1 expression in HCC cells by IL-17A was assessed by reverse transcription PCR, western blotting, and flow cytometry. Mechanistic studies were conducted with gene knockout models and pathway inhibitors. The function of IL-17A in immune evasion was explored through coculture of T cells and HCC cells. The effects of IL-17A on the malignant biological behaviors of HCC cells were evaluated in vitro, and the antitumor effects of an IL-17A inhibitor and its synergistic effects with a PD-L1 inhibitor were studied in vivo.

Results: IL-17A upregulated PD-L1 expression in HCC cells in a dose-dependent manner, whereas IL-17A receptor knockout or treatment with a small mothers against decapentaplegic 2 inhibitor diminished the PD-L1 expression induced by IL-17A. IL-17A enhanced the survival of HCC cells in the coculture system. IL-17A increased the viability, G2/M ratio, and migration of HCC cells and decreased the apoptotic index. Cyclin D1, VEGF, MMP9, and Bcl-1 expression increased after IL-17A treatment, whereas BAX expression decreased. The combination of IL-17A and PD-L1 inhibitors showed synergistic antitumor efficacy and increased cluster of differentiation 8 + T lymphocyte infiltration in an HCC mouse model.

Conclusion: IL-17A upregulates PD-L1 expression via the IL-17A receptor/phosphorylation-small mothers against decapentaplegic 2 signaling pathway in HCC cells. Blocking IL-17A enhances the therapeutic efficacy of PD-L1 antibodies in HCC in vivo.