The non-receptor tyrosine kinase ITK is required for type 1 regulatory T cell development

Abstract

Abstract Type 1 regulatory T (Tr1)cells lack the expression of Foxp3 but are potent producers of the immunosuppressive cytokine IL-10, with profound regulatory function in suppressing inflammation and promoting tolerance. Tr1 cells differentiate in response to signals engaging T cell receptor (TCR) and/or regulatory cytokine milieu. The non-receptor tyrosine kinase ITK is a key modulator downstream of TCR, playing critical role in T cell development and function. Using mouse models carrying Foxp3-RFP and IL-10-GFP dual reporters, we found that, in the absence of ITK, Foxp3− IL-10+ Tr1 cell development driven by TCR activation is severely impaired in various tissues (spleen, lymph nodes, lung, gut, and fat). Under Tr1 polarizing condition, naïve Foxp3− CD4+T cells isolated from WT mouse thymus and spleen can both give rise to Tr1cells, however, Itk−/− thymic and splenic naïve Foxp3− CD4+ T cells are deficient in Tr1 differentiation. Although Itk−/−CD4+ T cells proliferated under Tr1 differentiating conditions, they failed to up-regulate LAG3, CD49b, ICOS, PD-1, c-Maf, AHR, and IRF4 to levels observed in WT cells, suggesting that ITK is critical for Tr1 cell fate programming. Utilizing transgenic mouse model carrying an allele sensitive mutant of ITK that allows ITK kinase specific blockade by a small molecule 3MB-PP1, we also determined that the expression of the aforementioned markers is dependent on ITK kinas activity. Inhibiting ITK kinase activity also diminished Tr1 differentiation inhuman CD4+ T cells. We conclude that ITK is required for Tr1 cell development and targeting ITK signaling may be a strategy to modulate regulatory immunity for clinical benefit.