Search

The pleiotropic cytokine, transforming growth factor (TGF)-β, and CD4+CD25+Foxp3+ regulatory T cells (Tregs) play a critical role in actively suppressing antitumor immune responses. Evidence shows that TGF-β produced by tumor cells promotes tolerance via expansion of Tregs. Our group previously demonstrated that blockade of TGF-β signaling with a small molecule TGF-β receptor I antagonist (SM16) inhibited primary and metastatic tumor growth in a T cell dependent fashion. In the current study, we evaluated the effect of SM16 on Treg generation and function. Using BALB/c, FoxP3eGFP and Rag−/− mice, we performed FACS analysis to determine if SM16 blocked de novo TGF-β-induced Treg generation in vitro and in vivo. CD4+ T cells from lymph node and spleen were isolated from control mice or mice maintained on SM16 diet, and flow cytometry analysis was used to detect the frequency of CD4+CD25−FoxP3+ and CD4+CD25+FoxP3+ T cells. In vitro suppression assays were used to determine the ability to suppress naive T cell proliferation in vitro of both CD4+CD25+FoxP3+ and CD4+CD25−FoxP3+ T cell sub-populations. We then examined whether SM16 diet exerted an inhibitory effect on primary tumor growth and correlated with changes in FoxP3+expression. ELISA analysis was used to measure IFN-γ levels after 72 h co-culture of CD4+CD25+ T cells from tumor-bearing mice on control or SM16 diet with CD4+CD25− T cells from naive donors. SM16 abrogates TGF-β-induced Treg generation in vitro but does not prevent global homeostatic expansion of CD4+ T cell sub-populations in vivo. Instead, SM16 treatment causes expansion of a population of CD4+CD25−Foxp3+ Treg-like cells without significantly altering the overall frequency of Treg in lymphoreplete naive and tumor-bearing mice. Importantly, both the CD4+CD25−Foxp3+ T cells and the CD4+CD25+Foxp3+ Tregs in mice receiving SM16 diet exhibited diminished ability to suppress naive T cell proliferation in vitro compared to Treg from mice on control diet. These findings suggest that blockade of TGF-β signaling is a potentially useful strategy for blunting Treg function to enhance the anti-tumor response. Our data further suggest that the overall dampening of Treg function may involve the expansion of a quiescent Treg precursor population, which is CD4+CD25−Foxp3+.Other Information Published in: Journal of Translational Medicine License: http://creativecommons.org/licenses/by/4.0/See article on publisher's website: http://dx.doi.org/10.1186/s12967-019-1967-3

RORγt-expressing Tregs form a specialized subset of intestinal CD4+ Foxp3+ cells which is essential to maintain gut homeostasis and tolerance to commensal microbiota. Recently, c-Maf emerged as a critical factor in the regulation of RORγt expression in Tregs. However, aside from c-Maf signaling, the signaling pathways involved in the differentiation of RORγt+ Tregs and their possible interplay with c-Maf in this process are largely unknown. We show that RORγt+ Treg development is controlled by positive as well as negative signals. Along with c-Maf signaling, signals derived from a complex microbiota, as well as IL-6/STAT3- and TGF-β-derived signals act in favor of RORγt+ Treg development. Ectopic expression of c-Maf did not rescue RORγt expression in STAT3-deficient Tregs, indicating the presence of additional effectors downstream of STAT3. Moreover, we show that an inflammatory IFN-γ/STAT1 signaling pathway acts as a negative regulator of RORγt+ Treg differentiation in a c-Maf independent fashion.These data thus argue for a complex integrative signaling network that finely tunes RORγt expression in Tregs. The finding that type 1 inflammation impedes RORγt+ Treg development even in the presence of an active IL-6/STAT3 pathway further suggests a dominant negative effect of STAT1 over STAT3 in this process.

Foxp3-expressing regulatory T (Treg) cells can suppress the activity of various types of immune cells and play key roles in the maintenance of self-tolerance and in the regulation of immune responses against pathogens and tumor cells. Treg cells consist of heterogeneous subsets that have distinct phenotypes and functions. Upon antigen stimulation, naïve-like thymus-derived Treg cells, which circulate in secondary lymphoid organs, can differentiate into effector Treg (eTreg) cells and migrate to and control immune homeostasis of peripheral tissues. eTreg cells are heterogeneous in terms of their ability to localize to specific tissues and suppress particular types of immune responses. Differentiation and function of diverse eTreg subsets are regulated by a variety of transcription factors that are activated by antigens and cytokines. In this article, we review the current understanding of the transcriptional regulation of differentiation and function of eTreg cells.