Abstract
FOXP3 deficiency in mice and IPEX syndrome patients results in fatal autoimmunity by altering T regulatory cells (Treg). CD4+ T cells in IPEX patients and Foxp3-deficient mice were analyzed by single-cell cytometry and RNAseq, revealing heterogeneous Treg-like cells, some very similar to normal Tregs, others more distant. Conventional T cells showed no widespread activation or Th bias, but a monomorphic disease signature affected all CD4+ T cells, cell-extrinsic signature since extinguished in mixed bone marrow chimeric mice and heterozygous mothers of IPEX patients. Normal Tregs exerted dominant suppression, extinguishing the disease signature, and revealing in mutant Treg-like cells a small cluster of genes regulated cell-intrinsically by FOXP3, including key homeostatic regulators. We propose a two-step pathogenesis model: cell-intrinsic downregulation of core genes destabilizes Tregs, de-repressing systemic mediators which imprint the disease signature on all T cells, furthering Treg dysfunction. Accordingly, IL2 treatment improved the Treg-like compartment and survival.
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