T cell-intrinsic cGAS-CTCF regulation maintains regulatory T cell development and function [CTCF-CR]

Cyclic GMP-AMP synthase (cGAS) is a cytosolic double-strand DNA (dsDNA) sensor in innate immune cells. A function of cGAS is to detect cytosolic double-stranded DNA and synthesize the cyclic dinucleotide 2'3'-cGAMP. This second messenger binds to and activates the adaptor protein STING, triggering the TBK1-IRF3 signaling pathway. However, the function of cGAS in T cells remain unknown and its role in adaptive immunity is also poorly characterized. Here we show that nuclear cGAS promotes regulatory T cell (Treg) development by cooperating with the genome organizer CTCF through a T cell-intrinsic and synthase function-independent way. Conditional deletion of cGAS using Foxp3Cre-YFP Cgasfl/fl and CD4Cre Cgasfl/fl mice demonstrated that cGAS imprints thymocytes for Treg development before the expression of FOXP3. cGAS also promotes the FOXP3 inheritability and suppressive activity of Treg. At steady state, cGAS is located in the nucleus of Treg, while stimulation of naïve CD4+ T cell with anti-CD3/CD28 antibodies induces transcription of cGAS and its translocation into nucleus. ATAC-sequencing of thymic Treg and Treg precursors revealed that CTCF binding is reduced in mature Treg. Mechanistically, cGAS interacts with CTCF and recruits CTCF to Tnfrsf9 (4-1BB) and Tnfrsf4 (OX40) gene locus to maintain their stable transcription through formation of chromatin loops. Physiologically, in mouse tumor model, Treg specific deletion of cGAS reduced tumor growth. Therefore, we uncovered a T cell-intrinsic role of nuclear cGAS in maintaining Treg development and function by imprinting the genome architecture with CTCF.