Type 2 innate lymphoid cell suppression by regulatory T cells attenuates airway hyperreactivity and requires inducible T-cell costimulator–inducible T-cell costimulator ligand interaction

Background Atopic diseases, including asthma, exacerbate type 2 immune responses and involve a number of immune cell types, including regulatory T (Treg) cells and the emerging type 2 innate lymphoid cells (ILC2s). Although ILC2s are potent producers of type 2 cytokines, the regulation of ILC2 activation and function is not well understood. Objective In the present study, for the first time, we evaluate how Treg cells interact with pulmonary ILC2s and control their function. Methods ILC2s and Treg cells were evaluated by using in vitro suppression assays, cell-contact assays, and gene expression panels. Also, human ILC2s and Treg cells were adoptively transferred into NOD SCID γC-deficient mice, which were given isotype or anti–inducible T-cell costimulator ligand (ICOSL) antibodies and then challenged with IL-33 and assessed for airway hyperreactivity. Results We show that induced Treg cells, but not natural Treg cells, effectively suppress the production of the ILC2-driven proinflammatory cytokines IL-5 and IL-13 both in vitro and in vivo . Mechanistically, our data reveal the necessity of inducible T-cell costimulator (ICOS)–ICOS ligand cell contact for Treg cell–mediated ILC2 suppression alongside the suppressive cytokines TGF-β and IL-10. Using a translational approach, we then demonstrate that human induced Treg cells suppress syngeneic human ILC2s through ICOSL to control airway inflammation in a humanized ILC2 mouse model. Conclusion These findings suggest that peripheral expansion of induced Treg cells can serve as a promising therapeutic target against ILC2-dependent asthma.