Unstableregulatory and autoreactive effector T cells in patients with FOXP3 mutations
Studies of the monogenic autoimmune disease immunodysregulation polyendocrinopathy enteropathy X-linked syndrome (IPEX) have elucidated the essential function of the transcription factor FOXP3 and thymic-derived regulatory T cells (Tregs) in controlling peripheral tolerance. However, the presence and the source of autoreactive T cells in IPEX remain undetermined. Here, we investigated how FOXP3 deficiency affects the T cell receptor (TCR) repertoire and Treg stability in vivo and compared T cell abnormalities in patients with IPEX to those in patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED). To study Tregs independently of their phenotype and to analyze T cell autoreactivity, we combined Treg-specific demethylation region analyses, single-cell multi-omic profiling, and bulk TCR sequencing. We found that patients with IPEX, unlike patients with APECED, have expanded autoreactive T cells originating from both autoreactive effector T cells (Teffs) and Tregs. In addition, a fraction of the expanded Tregs lost their phenotypic and functional markers including CD25 and often also FOXP3.  Functional experiments with CRISPR/Cas9-mediated FOXP3 knock-out Treg and Tregs from patients with IPEX indicated that the patients' Tregs gain a Th2 skewed Teff-like function, which is consistent with immune dysregulation observed in these patients. Analyses of FOXP3 mutation-carrier mothers and a patient with IPEX after hematopoietic stem cell transplantation, indicated that Tregs expressing non-mutated FOXP3 prevent the accumulation of autoreactive Teffs and unstable Tregs. Collectively, we describe Treg instability and Teff autoreactivity in patients with IPEX. These findings could be directly used for diagnostic and prognostic purposes and for monitoring the effects of immunomodulatory treatments. Overall design: The study report scRNA seq, cell surface protein, and TCR data from CD4+ T cells from 3 healthy donors (HDs) and 3 patients with IPEX. The samples were hash tagged (1 HD and 1 IPEX), and analyzed ex vivo or after TCR stimulation.