Antigen receptor-mediated depletion of FOXP3 in induced regulatory T-lymphocytes via PTPN2 and FOXO1

Regulatory T-cells induced via IL-2 and TGFβ in vitro (iTreg) suppress immune cells and are potential therapeutics during autoimmunity. However, several reports described their re-differentiation into pathogenic cells in vivo and loss of their key functional transcription factor (TF) FOXP3 after T-cell antigen receptor (TCR)-signalling in vitro. Here, we show that TCR-activation antagonizes two necessary TFs for foxp3 gene transcription, which are themselves regulated by phosphorylation. Although the tyrosine phosphatase PTPN2 is induced to restrain IL-2-mediated phosphorylation of the TF STAT5, expression of the TF FOXO1 is downregulated and miR-182, a suppressor of FOXO1 expression, is upregulated. TGFβ counteracts the FOXP3-depleting TCR-signal by reassuring FOXO1 expression and by re-licensing STAT5 phosphorylation. Overexpressed phosphorylation-independent active versions of FOXO1 and STAT5 or knockdown of PTPN2 restores FOXP3 expression despite TCR-signal and absence of TGFβ. This study suggests novel targets for stabilisation and less dangerous application of iTreg during devastating inflammation.