A negative role for the interleukin-2-inducible T-cell kinase (ITK) in human Foxp3+ TREG 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 regulates Treg differentiation. However, whether Tec kinases modulate Treg development and/or function in human T cells remains unknown. Using a novel self-delivery siRNA platform (sdRNA), we found that ITK knockdown in primary human naive peripheral blood CD4 T cells increased Foxp3+ TREG differentiation under both Treg and T effector (Teff) cell priming conditions. ITK knockdown also enhanced the expression of the co-inhibitory receptor PD-1 on FoxP3+ T cells. Treg differentiated in vitro (iTreg) after ITK knockdown displayed suppressive capacity against effector CD4+ T cell proliferation. ITK knockdown decreased IL-17A production in T cells primed under Th17 conditions and increased Th1 differentiation. Finally, a dual ITK/RLK Tec kinase inhibitor blocked Treg differentiation and T cell activation in general. Our data suggest that targeting ITK in human T cells may be an effective approach to boost Treg in the context of autoimmune diseases, but non-specific inhibition of other Tec family kinases may broadly inhibit T cell activation.