Abstract
CD4+Foxp3+ regulatory T cells (Tregs) in the tumor microenvironment restrain antitumor immunity, resulting in tumor aggression and poor survival in hepatocellular carcinoma (HCC). CD8+CD122+ Tregs have been previously shown to be more potent in immunosuppression than are CD4+Foxp3+ Tregs. Previous studies have demonstrated that resveratrol exerts its anti-cancer effects by downregulating CD4+Foxp3+ and M2-like macrophages, two key immunoregulatory cells that maintain the immunosuppressive tumor microenvironment. In this study, we found that resveratrol inhibited the tumor growth in a subcutaneous Hepa1-6 HCC model and decreased the frequency of CD8+CD122+ Tregs in the tumor as well as lymph nodes and spleen of the tumor-bearing mice. It also increased the percentage of IFN-γ-expressing CD8+ T cells in the tumor and peripheral lymphoid organs. The antitumor effects of resveratrol were partially reversed by the adoptive transfer of exogenous CD8+CD122+ Tregs into the tumor-bearing mice. Meanwhile, resveratrol treatment downregulated immunosuppressive cytokines, including TGF-β1 and interleukin-10, in the tumor while elevating antitumor cytokines, TNF-α and IFN-γ. It also inhibited the activation of STAT3 signaling in the tumor. As expected, resveratrol reduced the percentage of M2-like macrophages in the mice. Importantly, resveratrol suppressed orthotopic H22 tumor growth and decreased the frequency of CD8+CD122+ Tregs and M2-like macrophages in the tumor-bearing mice. Furthermore, our studies showed that resveratrol, at non-cytotoxic concentrations, inhibited CD8+CD122+ Treg differentiation from CD8+CD122- T cells in vitro. Thus, our studies unveiled a new immune mechanism underlying the immunosuppressive tumor microenvironment and demonstrated that resveratrol could help reverse it by diminishing CD8+CD122+ Tregs.