Role of STAT3 in CD4+CD25+FOXP3+ Regulatory Lymphocyte Generation: Implications in Graft-versus-Host Disease and Antitumor Immunity

Abstract

Immunological tolerance is maintained by specialized subsets of T cells including CD4+CD25+FOXP3+ regulatory cells (Treg). Previous studies established that Treg thymic differentiation or peripheral conversion depend on CD28 and Lck signaling. Moreover, foxp3 gene transfer in murine CD4+CD25− T lymphocytes results in the acquisition of suppressive functions. However, molecular pathways leading to FOXP3 expression remain to be described. In this study, we investigated the molecular events driving FOXP3 expression. We demonstrated that CD28 activation in CD4+CD25− T lymphocytes leads to STAT3 Tyr705 phosphorylation in an Lck-dependent manner. STAT3 neutralization during naive peripheral CD4+CD25− T cell conversion into Treg through costimulation with TCR/CD28 and TGF-β1, decreased FOXP3 expression, prevented the acquisition of suppressive functions and restored the ability of the converted lymphocytes to produce IL-2 and IFN-γ. Furthermore, we observed that STAT3 ablation using small interfering RNA strategies inhibited FOXP3 expression and suppressive functions among naturally differentiated CD4+CD25+ T lymphocytes, suggesting a direct role of STAT3 in Treg phenotype and function maintenance. CD4+CD25+ T lymphocytes transduced with specific STAT3 small interfering RNA were devoid of suppressive functions and failed to control the occurrence of acute graft-vs-host disease. Finally, STAT3 inhibition in CD4+ lymphocytes enhanced the anti-tumor immunity conferred by a lymphocyte adoptive transfer. In summary, our findings determine that STAT3 is critical in the molecular pathway required for FOXP3 expression. STAT3 modulation should be taken into account when assessing how regulatory T cells contribute to inflammatory diseases and tumor immunosurveillance.

Transcription Factor Early Growth Response 3 Is Associated with the TGF-β1 Expression and the Regulatory Activity of CD4-Positive T Cells In Vivo

“…This observation was consistent with the previous report that TGF-b1 production was induced by the stimulation with anti-CD3 and anti-CD28 Abs in human CD4 + CD25 2 T cells (42). Moreover, costimulation of CD28 induces STAT3 phosphorylation in CD4 + CD25 2 T cells (43). We think STAT3 plays an important role, because enhanced phosphorylation of STAT3 in Egr-3-transduced cells was demonstrated under CD28 costimulation (Fig.…”

Regulation of NKG2D+CD8+T-cell-mediated antitumor immune surveillance: Identification of a novel CD28 activation-mediated, STAT3 phosphorylation-dependent mechanism

“…impaired the downstream phosphorylation of STAT3 in CD4 C T cells; 20 to answer this question, a pharmacologic model was used to measure NKG2D expression on mouse and human CD8 C T cells after CD28 stimulation in the presence or absence of the Lck inhibitor PP2, the JAK/STAT inhibitor AG490, or the STAT3 inhibitor JSI-124. As expected, activation of CD28 by CD80 binding elevated STAT3 phosphorylation as early as 15 min and NKG2D expression in CD8 C T cells.…”

“…A previous study demonstrated that CD28 triggers JAK/STAT3 signaling via Lck in CD4 C T cells. 20 We thus established a pharmacologic model to determine whether Lck/ZAP70, as an upstream kinase cascade, activates STAT3 in CD8 C T cells. Mouse and human CD8 C T cells were enriched (Fig.…”

“…19 Furthermore, CD28-induced Lck activation leads to phosphorylation of STAT3, whereas inhibition of Lck activity, or JAK/STAT3 signaling, blocks STAT3 phosphorylation and downstream cytokine production. 20 Nevertheless, how CD28 activation may affect NKG2D expression on CD8 C T cells has yet to be reported.…”

Mesenchymal Stem Cells Overexpressing IFN-β Inhibit Breast Cancer Growth and Metastases through Stat3 Signaling in a Syngeneic Tumor Model

“…Suppressing Treg has been shown to be effective in enhancing the immune response of host cells to cancer cells [31,32]. Importantly, studies have shown that constitutively activated Stat3 is involved in these events [33]. Taken together, this evidence suggests that constitutively activated Stat3 not only functions as an initiator for oncogenesis but is also involved in interactions between cancer cells and their microenvironment.…”