T cell-intrinsic STING signaling promotes regulatory T cell induction and immunosuppression by upregulating FOXP3 transcription in cervical cancer

<jats:sec><jats:title>Background</jats:title><jats:p>Stimulator of interferon genes (STING) is an innate immune sensor of cytoplasmic double-stranded DNA originating from microorganisms and host cells. The activation of cytosolic DNA-STING pathway in tumor microenvironments is usually linked to more robust adaptive immune responses to tumors, however the intracellular function of STING in regulatory T cells is largely unknown. In the present study, we aimed to explore the contribution of intracellular STING activation to regulatory T cell induction (iTreg) in cervical cancer (CC) microenvironments.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Blood samples and tumor specimens were obtained from patients with CC. The intratumoral STING, CCL22, CD8 and forkhead box P3 (FOXP3) expression levels were measured by immunohistochemistry. T cell-specific STING conditional knockout mice (CD4-Cre/STING<jats:sup>flox/flox</jats:sup>, TKO) were generated, and syngeneic TC-1 tumor model were investigated. The differentiation and molecular regulatory pathway of human and murine iTreg under different treatments were investigated by ex vivo assays, immunoblotting and quantitative PCR. Tumor-associated exosomes (T-EXO) were isolated from CC cell lines and exosomal contents were identified by ELISA and Western blot analysis. The impact of T-EXO on T cell differentiation was tested in in vitro cell culture.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Increased STING, CCL22 level, FOXP3<jats:sup>+</jats:sup> cells but decreased CD8<jats:sup>+</jats:sup> cells in tumor tissues predicted poor survival. Tumor-bearing CD4-Cre-STING<jats:sup>flox/flox</jats:sup> (TKO) mice displayed slower tumor growth tendencies as well as fewer FOXP3<jats:sup>+</jats:sup> cells but higher CD8<jats:sup>+</jats:sup> cell proportion in tumor tissues than wild-type (WT) mice. Activating of STING signaling cooperated with T cell receptor, interleukin-2 receptor and transforming growth factor-beta (TGF-β) signals to promote CD4<jats:sup>+</jats:sup>CD25<jats:sup>high</jats:sup>FOXP3<jats:sup>+</jats:sup> iTreg differentiation from both human and murine CD4<jats:sup>+</jats:sup>-naïve T cells from WT and IFNAR<jats:sup>−/−</jats:sup> mice but not TKO or IRF3<jats:sup>−/−</jats:sup> mice in vitro. Ectopic STING, TBK1 or IRF3 expression promoted iTreg differentiation from human CD4<jats:sup>+</jats:sup>-naïve T cells. T cell-intrinsic STING activation induced FOXP3 transcription through TBK1-IRF3-mediated SMAD3 and STAT5 phosphorylation independent of interferon-β. In CC, tumor-derived exosomes activated STING signaling in tumor-infiltrated T cells by exosomal TGF-β, cyclic GMP-AMP synthase and 2’-3’-cGAMP, leading to iTreg expansion.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>These findings highlight a novel mechanism for iTreg expansion mediated by tumor-derived exosome-activated T cell-intrinsic STING signal, and provide a rationale for developing immunotherapeutic strategies targeting STING signal in CC.</jats:p></jats:sec>