Interleukin-35 has a tumor-promoting role in hepatocellular carcinoma

Hepatic inflammatory response is a risk factor for liver cancer initiation and progression. Interleukin (IL)-35 is the newest member of the IL-12 cytokine family, and has been reported to play an essential role in the immunosuppressive liver microenvironment. Herein we focus on the expression profiles of IL-35 in hepatocellular carcinoma (HCC) and effects on local immune status. HCC transcriptome array data were downloaded from Gene Expression Omnibus (GEO). Analysis was performed by BRB-Array Tools and Ingenuity Pathway Analysis (IPA) software. Serum IL-35 level was detected by AimPlet bead-based immunoassay. In-situ IL-35 detection was performed by immunohistochemical staining and Western blot. The n-vitro effect of IL-35 on CD4⁺ or CD8⁺ T cell function was detected by flow cytometry. Our results showed that there were large amounts of IL-35 expressed in HCC serum and tumor tissues. IL-35 expression affects the transcript of thousands of genes, most differentially expressed genes (DEGs), in tumor tissues correlated with T cell immunity. The IL-35 high-expression group exhibited enhancement of regulatory T cells (T_regs ) and impairment of cytolytic T cells. In-vitro experiments proved that exogenous IL-35 stimulated the expression of programmed cell death 1 (PD-1) and lymphocyte activation gene-3 (LAG3) in CD4⁺ and CD8⁺ T cells. In addition, the stimulating effect was time-dependent. Furthermore, IL-35 inhibited interferon (IFN)-γ secretion by CD4⁺ and CD8⁺ T cells. Elevated IL-35 had an immune suppressive role in HCC tumor microenvironments through affecting inhibitor receptor expression and cytokine secretion of CD4⁺ and CD8⁺ T cells. Dissection of the precise targets and underlying molecular mechanisms would mean alternative treatments for HCC patients.