Date Published: April 25, 2019
Publisher: Public Library of Science
Author(s): Polina Mamontov, Ryan A. Eberwine, Jackie Perrigoue, Anuk Das, Joshua R. Friedman, J. Rodrigo Mora, Ciriaco A. Piccirillo.
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 (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 human primary naïve peripheral blood CD4 T cells increased Foxp3+ expression under both TREG and T helper priming conditions. TREG 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 TREG in the context of autoimmune diseases, but concomitant inhibition of other Tec family kinases may negate this effect.
Interleukin-2-inducible T-cell kinase (ITK) is a member of the Tec kinase family of non-receptor tyrosine kinases and mediates T cell signaling downstream of TCR activation . Signaling through ITK modulates T cell activation, T helper cell differentiation, and thymic selection of developing thymocytes. ITK has been implicated as a critical node in T cell and NK cell mediated inflammation, leading to interest in developing therapeutics to modulate ITK function in autoimmune and inflammatory diseases [2, 3]. ITK is thought to drive Th2-mediated disease such as allergic asthma, and ITK-/- mice exhibit significantly improved disease course and reduced bronchoconstriction after antigen re-challenge in ovalbumin sensitized mice [2, 4]. ITK has also been shown to regulate the balance between inflammatory CD4+ Th17 cells and CD4+ Foxp3+ regulatory T cells (TREG) in mice . In addition, ITK is an important switch for Th1 and Th2 mediated immunity, and murine ITK deficiency results in reduced differentiation and effector cytokine production from Th1, Th2, and Th17 polarized CD4+ T cells, while bolstering TREG development [5–8]; in contrast, some data suggest that ITK deficiency increases Th1 differentiation under some conditions . However, since ITK is also involved in thymocyte development, studies in ITK knock-out mice may not distinguish potential developmental defects in the immune system from the effects of ITK inhibition on the mature immune system . Although ITK also serves a non-kinase ‘scaffolding’ function for the docking of signaling intermediates , studies in kinase-dead ITK mutant mice have shown that kinase activity is required for driving Th1, Th2, and Th17 differentiation [6, 7], suggesting that a specific kinase-inhibitor may modulate ITK effects on T cell differentiation.
The Tec family of tyrosine kinases, including ITK and RLK, are critical for TCR-mediated T cell activation and T helper cell differentiation, and they are likely to play distinct roles in these processes. We show here for the first time that ITK is a negative regulator of human Foxp3+ TREG and Th1 development, with a reciprocal effect on Th17 differentiation. Our findings extend recent observations in ITK deficient mice, which display enhanced TREG development in vivo and in vitro and diminished T effector development and function [5, 6, 8].