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Functional validation of a novel STAT3 ‘variant of unknown significance’ identifies a new case of STAT3 GOF Syndrome and reveals broad immune cell defects

2025; Oxford University Press; Linguagem: Inglês

10.1093/cei/uxaf005

1365-2249

Joseph Mackie, Daniel Suan, Peter McNaughton, Filomeen Haerynck, Michael O’Sullivan, Antoine Guérin, S. Cindy, Stuart G. Tangye,

Chronic Lymphocytic Leukemia Research

Abstract Introduction STAT3 orchestrates crucial immune responses through its pleiotropic functions as a transcription factor. Patients with germline monoallelic dominant negative or hypermorphic STAT3 variants, who present with immunodeficiency and/or immune dysregulation, have revealed the importance of balanced STAT3 signaling in lymphocyte differentiation and function, and immune homeostasis. Here, we report a novel missense variant of unknown significance in the DNA binding domain of STAT3 in a patient who experienced hypogammaglobulinemia, lymphadenopathy, hepatosplenomegaly, immune thrombocytopenia, eczema and enteropathy over a 35-year period. Methods In vitro demonstration of prolonged STAT3 activation due to delayed de-phosphorylation, and enhanced transcriptional activity, confirmed this to be a novel pathogenic STAT3 gain-of-function variant. Peripheral blood lymphocytes from this patient, and patients with confirmed STAT3 Gain-of-function Syndrome, were collected to investigate mechanisms of disease pathogenesis. Results B cell dysregulation was evidenced by a loss of class-switched memory B cells and a significantly expanded CD19hiCD21lo B cell population, likely influenced by a skewed CXCR3+ TFH population. Interestingly, unlike STAT3 dominant negative variants, cytokine secretion by activated peripheral blood STAT3 GOF CD4+ T cells and frequencies of Treg cells were intact, suggesting CD4+ T cell dysregulation likely occurs at sites of disease rather than the periphery. Conclusion This study provides an in-depth case study in confirming a STAT3 gain-of-function variant and identifies lymphocyte dysregulation in peripheral blood of patients with STAT3 Gain-of-function Syndrome. Identifying cellular biomarkers of disease provide a flow cytometric based screen to guide validation of additional novel STAT3 gain-of-function variants as well as provide insights into putative mechanisms of disease pathogenesis.