Abstract
Signal transducer and activator of transcription 3 (STAT3) regulates gene expression downstream of cell surface cytokine and hormone receptors. Heterozygous germline loss of function STAT3 mutations lead to the primary immunodeficiency hyper-IgE syndrome while somatic activating STAT3 mutations recur in human solid organ and immune malignancies. Germline heterozygous activating STAT3 mutations result in early-onset autoimmunity with aspects of immunodeficiency. Affected individuals share characteristics with autoimmune lymphoproliferative syndrome and immunodysregulation polyendocrinopathy enteropathy X-linked syndrome, including reduced T regulatory cell numbers. They present with variable autoimmune symptoms including type 1 diabetes, rheumatoid arthritis, gut enteropathies and autoimmune cytopenias. Whilst many effects of STAT3 loss of function on immune cells have been described, the mechanisms behind autoimmunity and immunodeficiency in patients with activating STAT3 mutations remain unclear.
Here, we present a detailed characterisation of T cell development and maturation in young and old mice on two different backgrounds with Crispr-engineered germline activating mutations in two domains of STAT3. We use mixed chimeras, flow cytometry, T cell receptor deep sequencing and high throughput single-cell transcriptomics to reveal cell-extrinsic and -autonomous roles of overactive STAT3 in T cells in autoimmunity and immune malignancy. To our knowledge, this is the first report of mice with Stat3 germline activating mutations identical to those in autoimmunity or malignancy. We validate our key findings in humans with gain of function germline STAT3 mutations and childhood-onset autoimmunity.
