A negative role for the interleukin-2-inducible T-cell kinase (ITK) in human Foxp3(+) T(REG) differentiation

The Tec kinases ITK (interleukin-2-inducible T-cell kinase) and RLK (resting lymphocyte kinase) are critical components of the proximal TCR/CD3 signal transduction machinery, and data in mice suggest that ITK negatively modulates regulatory T cell (T(REG)) differentiation. However, whether Tec kinases modulate T(REG) development and/or function in human T cells remains unknown. Using a novel self-delivery siRNA platform (sdRNA), we found that ITK knockdown in human primary naïve peripheral blood CD4 T cells increased Foxp3(+) expression under both T(REG) and T helper priming conditions. T(REG) differentiated under ITK knockdown conditions exhibited enhanced expression of the co-inhibitory receptor PD-1 and were suppressive in a T cell proliferation assay. ITK knockdown decreased IL-17A production in T cells primed under Th17 conditions and promoted Th1 differentiation. Lastly, a dual ITK/RLK Tec kinase inhibitor did not induce Foxp3 in CD4 T cells, but conversely abrogated Foxp3 expression induced by ITK knockdown. Our data suggest that targeting ITK in human T cells may be an effective approach to boost T(REG) in the context of autoimmune diseases, but concomitant inhibition of other Tec family kinases may negate this effect.