CRISPR-Cas screen in ILC2 identifies Mef2d as a regulator of GATA3 and type-2 immunity [CRISPR screen]

Group 2 innate lymphoid cells (ILC2s) orchestrate tissue homeostasis, allergic disorders and anti-helminth protective immunity through their production of cytokines. However, their rarity has hampered high-throughput genetic screening approaches to uncover novel ILC2 regulators in an unbiased manner. We combined expansion of progenitors from multi-reporter mouse strains with optimised ILC differentiation cultures to perform CRISPR-Cas9 screens for regulators of ILC2 development and function. Mef2d emerged as a critical regulator of GATA3 and IL-13, and was essential for type-2 immunity as demonstrated by conditional Mef2d-deficient mice, including a Boolean-ILC2-Cre (BIC) mouse strain developed to enable ILC2-specific gene deletion. Mechanistically, Mef2d bound and transcriptionally repressed the Zc3h12a locus encoding the endonuclease Regnase-1, a negative regulator of IL-33 receptor (ST2) and GATA3 expression, thereby promoting IL-33-mediated ILC2 proliferation and cytokine production. Notably, in ILC2s Mef2d also acted downstream of leukotriene C4-induced calcium-mediated signalling to translocate NFAT1 to the nucleus to promote type-2 gene transcription. These Mef2d-mediated pathways converge and feedback to potentiate type-2 immunity. Overall design: To identify regulators of GATA3 and IL-13 expression during ILC development and differentiation we performed CRISPR screens using transcription factor and cytokine reporter mice to provide CLPs which were in vitro expanded and transduced with a sgRNA library targeting 1131 transcription factors