Signal Transducer And Activator Of Transcription 1 Gain-of-function Research Articles

Dysregulated IFN-γ signals promote autoimmunity in STAT1 gain-of-function syndrome

Heterozygous signal transducer and activator of transcription 1 ( STAT1 ) gain-of-function (GOF) mutations promote a clinical syndrome of immune dysregulation characterized by recurrent infections and predisposition to humoral autoimmunity. To gain insights into immune characteristics of STAT1-driven inflammation, we performed deep immunophenotyping of pediatric patients with STAT1 GOF syndrome and age-matched controls. Affected individuals exhibited dysregulated CD4 + T cell and B cell activation, including expansion of T H 1-skewed CXCR3 + populations that correlated with serum autoantibody titers. To dissect underlying immune mechanisms, we generated Stat1 GOF transgenic mice ( Stat1 GOF mice) and confirmed the development of spontaneous humoral autoimmunity that recapitulated the human phenotype. Despite clinical resemblance to human regulatory T cell (T reg ) deficiency, Stat1 GOF mice and humans with STAT1 GOF syndrome exhibited normal T reg development and function. In contrast, STAT1 GOF autoimmunity was characterized by adaptive immune activation driven by dysregulated STAT1-dependent signals downstream of the type 1 and type 2 interferon (IFN) receptors. However, in contrast to the prevailing type 1 IFN-centric model for STAT1 GOF autoimmunity, Stat1 GOF mice lacking the type 1 IFN receptor were only partially protected from STAT1-driven systemic inflammation, whereas loss of type 2 IFN (IFN-γ) signals abrogated autoimmunity. Last, germline STAT1 GOF alleles are thought to enhance transcriptional activity by increasing total STAT1 protein, but the underlying biochemical mechanisms have not been defined. We showed that IFN-γ receptor deletion normalized total STAT1 expression across immune lineages, highlighting IFN-γ as the critical driver of feedforward STAT1 elevation in STAT1 GOF syndrome.

The human Stat1 gain-of-function T385M mutation causes expansion of activated T-follicular helper/T-helper 1-like CD4 T cells and sex-biased autoimmunity in specific pathogen-free mice.

Humans with gain-of-function (GOF) mutations in STAT1 (Signal Transducer and Activator of Transcription 1), a potent immune regulator, experience frequent infections. About one-third, especially those with DNA-binding domain (DBD) mutations such as T385M, also develop autoimmunity, sometimes accompanied by increases in T-helper 1 (Th1) and T-follicular helper (Tfh) CD4 effector T cells, resembling those that differentiate following infection-induced STAT1 signaling. However, environmental and molecular mechanisms contributing to autoimmunity in STAT1 GOF patients are not defined. We generated Stat1T385M/+ mutant mice to model the immune impacts of STAT1 DBD GOF under specific-pathogen free (SPF) conditions. Stat1T385M/+ lymphocytes had more total Stat1 at baseline and also higher amounts of IFNg-induced pStat1. Young mutants exhibited expansion of Tfh-like cells, while older mutants developed autoimmunity accompanied by increased Tfh-like cells, B cell activation and germinal center (GC) formation. Mutant females exhibited these immune changes sooner and more robustly than males, identifying significant sex effects of Stat1T385M-induced immune dysregulation. Single cell RNA-Seq (scRNA-Seq) analysis revealed that Stat1T385M activated transcription of GC-associated programs in both B and T cells. However, it had the strongest transcriptional impact on T cells, promoting aberrant CD4 T cell activation and imparting both Tfh-like and Th1-like effector programs. Collectively, these data demonstrate that in the absence of overt infection, Stat1T385M disrupted naïve CD4 T cell homeostasis and promoted expansion and differentiation of abnormal Tfh/Th1-like helper and GC-like B cells, eventually leading to sex-biased autoimmunity, suggesting a model for STAT1 GOF-induced immune dysregulation and autoimmune sequelae in humans.

Chronic mucocutaneous candidiasis and immune dysregulation due to STAT1 Gain of Function

BackgroundGermline gain-of-function (GOF) mutations in the Signal Transducer and Activator of Transcription 1 (STAT1) gene have been associated with autosomal dominant chronic mucocutaneous candidiasis (CMCC), autoimmune and inflammatory manifestations. Although most patients with STAT1 GOF have CMCC, the disease has a broad phenotypic spectrum.Case Description: A 13-year-old male born to non-consanguineous parents with a past medical history of chronic mucocutaneous candidiasis, autoimmune hypothyroidism, and recurrent viral respiratory tract infections presented for immune evaluation. His medical history was also significant for chronic fatigue refractory to thyroid replacement therapy, chronic paronychia, oral thrush, pneumonia requiring hospitalization, recurrent chalazia status post excision, and prolonged tonsillitis. Laboratory results showed high total serum IgG levels with elevated IgG1 and IgG3 subclasses, elevated B cell counts with atypical lymphocytes, and chronic EBV-viremia. He had no clinical or laboratory evidence of active lymphoproliferative disease. He had normal lymphocyte proliferation to mitogens with impaired response to antigens. He had an adequate humoral response to protein and polysaccharide antigens. Targeted genetic testing for inborn errors of immunity showed a heterozygous variant in the STAT1 gene (c.1169T>C, p.MET390Thr), which had been previously reported in patients with STAT1 GOF. The patient was treated with oral fluconazole with interval improvement in CMCC and subsequently maintained on prophylactic fluconazole and TMP/SMX. He had an unremarkable family history, which suggests a de novo mutation in STAT1. ConclusionThe presence of CMCC and autoimmunity should raise concern for STAT1 GOF. Genetic testing for inborn errors of immunity can be a valuable tool in the diagnosis of patients with CMCC and can help guide therapy. Unfortunately, hematopoietic stem cell transplant has been associated with a high mortality rate in patients with STAT1 GOF. JAK inhibition therapy was recommended for this patient. However, there is currently no consensus regarding JAK inhibitor selection, dosing, treatment duration or biomarkers in STAT1 GOF.

Myocarditis in a congenital STAT1 gain-of-function patient

Autosomal dominant Signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations result in an inborn error of immunity characterized by chronic mucocutaneous candidiasis, recurrent viral and bacterial infections, and diverse autoimmune manifestations. Current treatment consists of chronic antifungal therapy, antibiotics for concomitant infections, and immunosuppressive therapy in case of autoimmune diseases. More recently, treatment with Janus kinases 1 and 2 (JAK1/2) inhibitors have shown promising yet variable results. We describe a STAT1 GOF patient with an incidental finding of elevated cardiac troponins, leading to a diagnosis of a longstanding, slowly progressive idiopathic myocarditis, attributed to STAT1 GOF. Treatment with a JAKinhibitor (baricitinib) mitigated cardiac inflammation on MRI but was unable to alter fibrosis, possibly due to the diagnostic delay, which finally led to fatal arrhythmia. Our case illustrates that myocarditis can be part of the heterogeneous disease spectrum of STAT1 GOF. Given the insidious presentation in our case, we recommend a low treshold for cardiac evaluation in all STAT1 GOF patients. [Display omitted] [Display omitted]

Novel STAT1 gain-of-function variant in a patient with Bechet’s like clinical phenotype

Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that mediates cellular responses to interferons (IFNs), multiple cytokines and growth factors in diverse cell types. STAT1 gain-of-function (GOF) variants are predominantly associated with chronic mucocutaneous candidiasis (CMC), with majority of the variants confined to the coiled-coil domain (CCD) and the DNA-binding domain (DBD) of STAT1. Here, we present the case of a female child with a novel STAT1 variant who presented with recurrent, severe aphthous ulcers and cutaneous ulceration, but with absence of CMC. She first presented at age 1 year with recurrent fevers. She later developed recurrent oral ulcers, genital ulcers, skin lesions including frequent periungual edema and erythema with rare pustules or hemorrhagic crust, ulcers of the digits and extremities, ulcerative scalp lesions with occasional pustules, and perioral and nasal scaly pink papules consistent with periorofacial dermatitis. She was diagnosed with Bechet’s syndrome and started on colchicine which led to clinical improvement of her ulcers and skin disease. Clinical sequencing and research-based exome sequencing (ES) revealed a de novo novel heterozygous missense mutation (c.1676A>G, p.Glu559Gly) localized in the linker domain of STAT1, without other candidate genes to explain her clinical phenotype. Immunophenotyping revealed reduced memory and class-switched memory B cells and a unique finding of elevated levels of TCRab-positive double negative T cells (~13–20%). A functional STAT1 phosphorylation assay revealed significantly higher levels of STAT1 phosphorylation in patient monocytes after stimulation with IFNγ (25 ng/mL) compared to controls. An elevated level of total STAT1 protein at baseline and after IFNγ stimulation was also detected in the patient cells, providing strong supporting evidence for the pathogenicity of the identified variant. This novel variant and few similar cases reported previously expands the growing clinical phenotype of STAT1 GOF disease to include a Behcet’s-like clinical phenotype in the absence of CMC.

Clinical Variability of STAT3 GOF Amongst a Single-Family Cohort

Gain-of-function (GOF) mutations in signal transducer and activator of transcription 3 (STAT3) have been linked to a diverse phenotype consisting of early-onset autoimmunity, lymphoproliferation, and immunodeficiency. Here we present a single-family cohort with STAT3 GOF mutations to illustrate the variability in clinical presentation of this disorder.

Deep Immune Profiling of Patients with STAT1 Gain-of-Function: Revealing New Mechanisms of Pathology

Background: Patients with heterozygous signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) pathogenic variants exhibit an array of clinical phenotypes including susceptibility to multiple infections, autoimmunity, and cancer predisposition. Previous studies to characterize the pathways involved and explore therapeutic interventions have been constrained by the technology to perform in-depth immunophenotyping. Mass cytometry has allowed us to perform extensive immune profiling of patients with inborn errors of immunity (IEI) to help gain a better understanding of disease pathology. STAT1 gain-of-function (GOF) mutations have demonstrated higher levels of phosphorylated STAT1 in response to type I and II interferons, but the response to other cytokines is less understood. Using advanced cytometry, we demonstrate a unique pattern of STAT1 phosphorylation in response to IL-6 stimulation in T-cell subsets and this differential pattern may play a role in T-cell differentiation and memory in STAT1 GOF patients.Cases: We report two patients with heterozygous STAT1 GOF mutations in the coiled-coil domain. For both patients, the clinical phenotype was largely consistent with other STAT1 GOF patients, one (P1, c.800C>T; p.ala267Val) presented with secondary HLH due to histoplasmosis, and the second (P2, c.866A>G; p.Tyr289Cys) presented with presumed vaccine strain varicella zoster virus (VZV) meningitis and subsequent history of recurrent herpes simplex virus (HSV) skin lesions. Patient peripheral blood mononuclear cells (PBMCs) were evaluated by fluorescence flow cytometry and cytometry by time of flight (CyTOF) as previously described (Roussel et al. J Leukoc Biol. 2017) to evaluate the impact of STAT1 GOF mutations on T-cell immunophenotype and cytokine signaling.Results: Utilizing cytometric data, we were able to identify similar patterns of T cell distribution on t-distributed stochastic neighbor embedding (t-SNE) plots for both patients with STAT1 GOF that were distinct compared to healthy controls (Fig 1a). In the T-cell compartment, both patients had decreased Th17 and Treg populations and an increased Th1/Th2 ratio compared to healthy donor (Fig 1b). In response to stimulation with IFNg or IL-6, there were also clear patterns with the two patients compared to healthy controls. Levels of p-STAT1 and p-STAT3 were assessed in STAT1 GOF and health donor PBMCs at several times points between 15 and 120 minutes, after stimulation with either IFNg or IL-6. Using fluorescence flow, we found that IL-6 stimulation led to greater than anticipated p-STAT1 response at all timepoints compared to a much more muted response to IFNg. The cell subsets highlighted in the t-SNE after IL-6 stimulation differ from the cell subsets that respond to IFNg stimulation in patients and healthy control (Fig 2a), suggesting that distinct cell populations are driving the response to IL-6. By evaluating these IL-6 responsive subsets in comparison with healthy control by CyTOF, we identified an exaggerated p-STAT1 response to IL-6 in the memory T-cell populations in P2 (Fig 2b).Conclusions: These two unique clinical presentations demonstrate that with similar mutations in the coiled-coil domain of STAT1, yet largely differing clinical presentations, the immune profiling patterns of the patients compared to healthy controls can drive further work on disease characterization and therapeutic interventions. This is relevant for this patient cohort, as treatment recommendations for STAT1 GOF are not well established. Long-term outcomes with JAK inhibition are lacking and transplant survival rates to date have been very poor compared to other immune diseases including familial HLH. With identification of IL-6 signaling playing a potential role in T-cell maturation, further studies will need to be performed to determine if IL-6 modulation could be used as a treatment modality. We conclude that performing deep immunophenotyping of patients with inborn errors of immunity (IEIs) such as STAT1 GOF can point to new disease mechanisms of human immunity and inflammation and lead to improved understanding of the role of cytokine and cellular signaling in normal hematopoiesis and cellular maturation. [Display omitted] DisclosuresRathmell: Sitryx: Consultancy, Current equity holder in publicly-traded company, Research Funding; Caribou: Consultancy, Current equity holder in publicly-traded company, Current holder of stock options in a privately-held company; Nirogy: Consultancy, Current holder of stock options in a privately-held company; Merck: Speakers Bureau; Pfizer: Speakers Bureau; Mitobridge: Consultancy; Incyte: Research Funding; Calithera: Research Funding; Tempest: Research Funding.

STAT1 gain-of-function heterozygous cell models reveal diverse interferon-signature gene transcriptional responses

Signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) is an autosomal dominant immune disorder marked by wide infectious predisposition, autoimmunity, vascular disease, and malignancy. Its molecular hallmark, elevated phospho-STAT1 (pSTAT1) following interferon (IFN) stimulation, is seen consistently in all patients and may not fully account for the broad phenotypic spectrum associated with this disorder. While over 100 mutations have been implicated in STAT1 GOF, genotype–phenotype correlation remains limited, and current overexpression models may be of limited use in gene expression studies. We generated heterozygous mutants in diploid HAP1 cells using CRISPR/Cas9 base-editing, targeting the endogenous STAT1 gene. Our models recapitulated the molecular phenotype of elevated pSTAT1, and were used to characterize the expression of five IFN-stimulated genes under a number of conditions. At baseline, transcriptional polarization was evident among mutants compared with wild type, and this was maintained following prolonged serum starvation. This suggests a possible role for unphosphorylated STAT1 in the pathogenesis of STAT1 GOF. Following stimulation with IFNα or IFNγ, differential patterns of gene expression emerged among mutants, including both gain and loss of transcriptional function. This work highlights the importance of modeling heterozygous conditions, and in particular transcription factor-related disorders, in a manner which accurately reflects patient genotype and molecular signature. Furthermore, we propose a complex and multifactorial transcriptional profile associated with various STAT1 mutations, adding to global efforts in establishing STAT1 GOF genotype–phenotype correlation and enhancing our understanding of disease pathogenesis.

Clinical and Immunological Heterogeneity in Japanese Patients with Gain-of-Function Variants in STAT3.

Germline loss-of-function variants in the signal transducer and activator of transcription 3 (STAT3) gene result in autosomal dominant hyper IgE syndrome, whereas somatic gain-of-function (GOF) variants in STAT3 are associated with some malignancies. In addition, germline GOF variants in STAT3 are linked to disorders involving autoimmunity and lymphoproliferation. In this study, we describe five Japanese families with germline GOF variants in STAT3, including three novel variants. We also present the clinical and immunological characteristics of these patients. Eight patients from five families were enrolled in this study. We performed genetic and immunological analyses, and collected the associated clinical information. We identified five heterozygous variants in STAT3 using whole-exome sequencing and target gene sequencing. Two of these (E286G and T716M) were previously reported and three (K348E, E415G, and G618A) were novel. A STAT3 reporter assay revealed that all of the variants were GOF. However, the immunological and clinical characteristics among the patients were highly variable. Patients with STAT3 GOF variants exhibited clinical and immunological heterogeneity with incomplete penetrance.

The pathogenic T387A missense mutation in the gene encoding signal transducer and activator of transcription 1 exhibits a differential gene expression profile

Heterozygous gain-of-function (GOF) mutations in the interferon-driven transcription factor STAT1 (signal transducer and activator of transcription 1) cause chronic mucocutaneous candidiasis (CMC). In this study, we characterized the molecular basis of a CMC-associated missense mutation by introducing a threonine-to-alanine exchange in the STAT1 DNA-binding domain at position 387. This substitution had previously been described in a CMC patient with suppurative eyelid infection and cutaneous abscesses, which are both unusual symptoms in this immunodeficiency. The STAT1-T387A mutant generated was compared to the wild-type protein and, in addition, to the missense mutant in the neighbouring position 386. Our results showed that the T387A mutant displayed distinct properties different from the wild-type molecule, namely elevated levels of tyrosine phosphorylation in conjunction with increased DNA-binding activity, hyperactive transcriptional regulation, and prolonged nuclear accumulation. The elevated tyrosine phosphorylation of the T387A mutant did not result in an increased mRNA production above the level of the wild-type molecule for all transcripts tested, indicating that the transcriptional activity of this mutant is largely gene-dependent. Nonetheless, these data demonstrate that the pathogenic T387A mutation associated with an atypical CMC symptomatology is biochemically similar to other well-characterized GOF mutants, while the H386A mutant was indistinguishable from the wild-type molecule. Our findings are in line with the assumption that the phenotype of this dominant STAT1 GOF mutation probably results from a disturbed shift in the equilibrium between the parallel and antiparallel dimer conformation, which is required for physiological gene activation.

The clinical, immunological and genetic features of 12 Chinese patients with STAT3 mutations

BackgroundLoss-of-function (LOF) mutations in signal transducer and activator of transcription 3 (STAT3) is one of the causes of STAT3 hyperimmunoglobulin E (IgE) syndrome (STAT3-HIES), while gain-of-function (GOF) mutations in STAT3 lead to immune dysregulation diseases. We retrospectively analyzed the age, common clinical symptoms, immunologic and molecular manifestations in 11 patients with LOF STAT3 mutations and 1 patient with a GOF STAT3 mutation.MethodsTwelve patients were enrolled in our study. Serum immunoglobulin measurements, lymphocyte subset detection and whole-exome sequencing were performed.ResultsThe median age at diagnosis of STAT3-HIES patients was 4.74 years. Eczema, recurrent respiratory infections, fevers, abscesses and Staphylococcus aureus infections were the classic manifestations. Elevated serum IgE levels are not always observed in conjunction with high eosinophil counts. A moderate viral DNA load was also measured in peripheral blood mononuclear cells. We noticed that c. 1144C>T was the most common mutation site, followed by c.1311C>A. Additionally, c.1311C>A and c. 1826G>C are two novel mutations. Eight patients achieved notable improvement after receiving intravenous immunoglobulin.ConclusionWe updated the current knowledge of this topic. We found an earlier median age at diagnosis, a higher survival rate, and a general lack of nonimmunological abnormalities; we also described the treatment details and novel mutations involve in STAT3-HIES and compared STAT3 LOF and GOF mutations.

Live Cell Imaging Demonstrates Multiple Routes Toward a STAT1 Gain-of-Function Phenotype.

Signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations result in a primary immunodeficiency (PID) characterized typically by chronic mucocutaneous candidiasis (CMC), but a wider phenotypic range is reported and remains unexplained from a pathophysiological point-of-view. We hypothesized that different STAT1 GOF mutations may result in distinct molecular mechanisms, possibly explaining the variable phenotypes observed in patients. We selected STAT1 GOF mutants (R274W, R321S, T419R, and N574I) that are spread over the protein and studied their dynamic behavior in vitro in U3A and HeLa cell lines. All GOF mutants showed increased STAT1 phosphorylation compared to STAT1 WT. Real-time imaging demonstrated three underlying mechanisms for STAT1 GOF: (i) R274W showed a faster nuclear accumulation, (ii) both R321S and N574I showed a reduced nuclear mobility and slower dephosphorylation, whereas (iii) T419R was near-immobile in the nucleus, potentially due to enhanced binding to chromatin.

Jakinibs for the Treatment of Immune Dysregulation in Patients With Gain–of–Function Signal Transducer and Activator of Transcription 1 (STAT1) or STAT3 Mutations

To investigate the efficacy of jakinib therapy in patients with gain-of-function (GOF) signal transducer and activator of transcription 1 (STAT1) or signal transducer and activator of transcription 3 (STAT3) mutations.The study included 17 total patients with either a STAT1 GOF (n = 11) or STAT3 GOF (n = 6) mutation who were treated with jakinibs (ruxolitinib or tofacitinib). Patients came from 11 international centers.This was a retrospective study to describe disease-related clinical manifestations and determine indication for treatment, dosage, length of treatment, treatment response, and treatment-associated complications. All subjects underwent thorough pre- and posttreatment clinical and laboratory evaluations and follow-up (follow-up period: 1–34 months).Fourteen patients (82%) responded favorably with clinical improvement to jakinib treatment. Observed clinical improvements included resolution of enteropathy leading to total parenteral nutrition independence, better lung function, improved autoimmune cytopenias, decreased arthritis symptoms, and remission of hemophagocytic lymphohistiocytosis. All patients with STAT1 GOF had resolved chronic mucocutaneous candidiasis with treatment. Most patients tolerated the jakinibs well with minimal or transient adverse effects. An increase in herpes zoster infections (none systemic and all cleared with antiviral agents) was observed in some patients. Four patients died despite treatment with a jakinib. The majority of these patients were critically ill with severe invasive infection or progressive lung disease. One patient died due to posttransplant complications.Jakinibs are both safe and effective in the treatment of patients with STAT1 or STAT3 GOF mutations with clinical manifestations of autoimmunity and/or immune dysregulation.Patients with STAT1 and STAT3 GOF mutations often present in early childhood with severe and/or refractory infections, lymphoproliferation, autoinflammation, and autoimmunity. Jakinibs allow for a targeted therapeutic approach to block the cytokine-induced JAK activation in STAT1 and STAT3 GOF diseases. This is the first study to evaluate the use and clinical impact of jakinibs in STAT1 and STAT3 GOF. The results are overwhelmingly encouraging, with the majority of patients having clinical improvement and reduction or resolution of autoimmune manifestations after treatment with a jakinib. Use of jakinibs late in disease progression or when critically ill was associated with mortality, suggesting early initiation may improve efficacy. This study has significant clinical impact in the treatment of STAT1 and STAT3 GOF and reinforces the notion that early genetic diagnosis of primary immunodeficiency diseases may lead to targeted therapeutic options and improved clinical outcomes.

Molecular and Phenotypic Characterization of Nine Patients with STAT1 GOF Mutations in China.

Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that mediates cellular responses to interferons (IFNs) and other cytokines and growth factors in diverse cell types. STAT1 gain-of-function (GOF) mutations result in an unexpectedly wide range of clinical features. It remains unclear why STAT1 GOF mutations result in such a broad spectrum of phenotypes. We analyzed the clinical, molecular, and phenotypic characteristics of nine Chinese patients with STAT1 GOF mutations. This study enrolled nine patients with STAT1 GOF mutations including five novel mutations. We discuss the molecular and phenotypic characterization such as unique Penicillium marneffei lymphadenitis. Patients with STAT1 GOF mutations had defects in both innate and adaptive immunity, including impaired T cell receptor (TCR) diversity; reduced numbers of naïve and effector memory CD4+ T cells, memory B cells, and NK cells; and defects in the production of IL-17A and IFN-γ. In addition, experiments with primary immune cells revealed that enhanced STAT1 phosphorylation resulted from not only lower rates of STAT1 dephosphorylation but also increased total STAT1 expression. Our report provides the first comprehensive overview of the molecular genetics, clinical heterogeneity, and underlying immunological abnormalities of patients with STAT1 GOF mutations in China. In further study, to find the relationship between different STAT1 GOF mutations and clinical phenotype as well as the mechanism of increased total STAT1 expression will be needed.

The activating p.Ser466Arg change in STAT1 causes a peculiar phenotype with features of interferonopathies

Signal Transducer and Activator of Transcription 1 (STAT1) is a DNA-binding signal transducer that regulates transcription of specific genes in response to IFNγ and IFNα/β stimulation. Loss-of-function mutations impairing STAT1 activity are known to confer susceptibility to intracellular bacterial and viral diseases. Conversely, the few known activating mutations of STAT1 allow predisposition to chronic mucocutaneous candidiasis disease, and occur in patients with combined immunodeficiency and defective Th1 and Th17 responses. Here, we report on a de novo gain-of-function (GoF) STAT1 mutation (c.1398C>G, p.Ser466Arg) identified by exome sequencing in an individual with brain calcification, arthritis, recurrent pericarditis, leukopenia, thrombocytopenia and low C3 levels, a phenotype resembling an interferonopathy. The Ser466Arg change affects a highly conserved residue located in the DNA binding domain of the protein and the amino acid substitution was documented to have an activating role both in vitro and in vivo. Altogether, clinical features and functional studies are compatible with hyperactivation of the Interferon pathways, highlighting a role of STAT1 GoF mutation in clinical phenotypes fitting interferonopathies.

Clinical Aspects of STAT3 Gain-of-Function Germline Mutations: A Systematic Review

Signal transducer and activator of transcription 3 (STAT3) gain-of-function (GOF) germline mutations have been recently described. A comprehensive overview of this early-onset multiorgan autoimmune and lymphoproliferative disease has not yet been compiled. We have conducted a systematic review of published STAT3 GOF cases to describe clinical, diagnostic, and therapeutic aspects of the disease. A systematic review including articles published before October 10, 2018, in PubMed, Web of Science, and Cochrane Central Register of Controlled Trials databases was performed. We described cases of patients with STAT3 GOF germline mutations with genetic analysis and a concordant phenotype if functional analyses were not performed for the mutation. The search identified 18 publications describing 42 unique patients. Twenty-eight different mutations were described. Onset of disease was very early with an average age of 3 (0.5-5) years. The most frequent manifestations were autoimmune cytopenias (28 of 42), lymphoproliferation (27 of 42), enteropathy (24 of 42), interstitial lung disease (15 of 42), thyroiditis (13 of 42), diabetes (10 of 42), and postnatal growth failure (15 of 21). Immunodeficiency was not always a predominant feature. Most patients required significant immunosuppressive therapy. Five patients received hematopoietic stem cell transplantation, and 4 died from complications. Improvement of symptoms was observed for 8 of 9 patients who received targeted biotherapies. STAT3 GOF syndrome is a new clinical entity to consider when confronted with a patient with early-onset polyautoimmunity, lymphoproliferation, and growth failure. At this time, precise therapeutic guidelines are lacking, but use of anti-IL-6 receptor and JAK inhibitor biologics is an attractive possibility.

Ruxolitinib partially reverses functional natural killer cell deficiency in patients with signal transducer and activator of transcription 1 (STAT1) gain-of-function mutations

Natural killer (NK) cells are critical innate effector cells whose development is dependent on the Janus kinase-signal transducer and activator of transcription (STAT) pathway. NK cell deficiency can result in severe or refractory viral infections. Patients with STAT1 gain-of-function (GOF) mutations have increased viral susceptibility. We sought to investigate NK cell function in patients with STAT1 GOF mutations. NK cell phenotype and function were determined in 16 patients with STAT1 GOF mutations. NK cell lines expressing patients' mutations were generated with clustered regularly interspaced short palindromic repeats (CRISPR-Cas9)-mediated gene editing. NK cells from patients with STAT1 GOF mutations were treated invitro with ruxolitinib. Peripheral blood NK cells from patients with STAT1 GOF mutations had impaired terminal maturation. Specifically, patients with STAT1 GOF mutations have immature CD56dim NK cells with decreased expression of CD16, perforin, CD57, and impaired cytolytic function. STAT1 phosphorylation was increased, but STAT5 was aberrantly phosphorylated in response to IL-2 stimulation. Upstream inhibition of STAT1 signaling with the small-molecule Janus kinase 1/2 inhibitor ruxolitinib invitro and invivo restored perforin expression in CD56dim NK cells and partially restored NK cell cytotoxic function. Properly regulated STAT1 signaling is critical for NK cell maturation and function. Modulation of increased STAT1 phosphorylation with ruxolitinib is an important option for therapeutic intervention in patients with STAT1 GOF mutations.

A Novel Heterozygous Mutation in the STAT1 SH2 Domain Causes Chronic Mucocutaneous Candidiasis, Atypically Diverse Infections, Autoimmunity, and Impaired Cytokine Regulation.

Chronic mucocutaneous candidiasis (CMC) is a primary immunodeficiency characterized by persistent or recurrent skin and mucosal surface infections with Candida species. Different gene mutations leading to CMC have been identified. These include various heterozygous gain-of-function (GOF) mutations in signal transducer and activator of transcription 1 (STAT1) that are not only associated with infections but also with autoimmune manifestations. Recently, two STAT1 GOF mutations involving the Src homology 2 (SH2) domain have been reported, while so far, over 50 mutations have been described mainly in the coiled coil and the DNA-binding domains. Here, we present two members of a Dutch family with a novel STAT1 mutation located in the SH2 domain. T lymphocytes of these patients revealed STAT1 hyperphosphorylation and higher expression of STAT1 target genes. The clinical picture of CMC in our patients could be explained by diminished production of interleukin (IL)-17 and IL-22, cytokines important in the protection against fungal infections.

Gain-of-function STAT1 mutations are associated with intracranial aneurysms

Chronic mucocutaneous candidiasis, characterized by persistent or recurrent fungal infections, represents the clinical hallmark in gain-of-function (GOF) signal transducer and activator of transcription 1 (STAT1) mutation carriers. Several cases of intracranial aneurysms have been reported in patients with GOF STAT1 mutation but the paucity of reported cases likely suggested this association still as serendipity. In order to endorse this association, we link the development of intracranial aneurysms with STAT1 GOF mutation by presenting the two different cases of a patient and her mother, and demonstrate upregulated phosphorylated STAT4 and IL-12 receptor β1 upon stimulation in patient's blood cells. We also detected increased transforming growth factor (TGF)-β type 2 receptor expression, particularly in CD14+ cells, and a slightly higher phosphorylation rate of SMAD3. In addition, the mother of the patient developed disseminated bacille Calmette-Guérin disease after vaccination, speculating that GOF STAT1 mutations may confer a predisposition to weakly virulent mycobacteria.

Ruxolitinib reverses dysregulated T helper cell responses and controls autoimmunity caused by a novel signal transducer and activator of transcription 1 (STAT1) gain-of-function mutation

Gain-of-function (GOF) mutations in the human signal transducer and activator of transcription 1 (STAT1) manifest in immunodeficiency and autoimmunity with impaired TH17cell differentiation and exaggerated responsiveness to type I and II interferons. Allogeneic bone marrow transplantation has been attempted in severely affected patients, but outcomes have been poor. We sought to define the effect of increased STAT1 activity on T helper cell polarization and to investigate the therapeutic potential of ruxolitinib in treating autoimmunity secondary to STAT1 GOF mutations. We used invitro polarization assays, as well as phenotypic and functional analysis of STAT1-mutated patient cells. We report a child with a novel mutation in the linker domain of STAT1 who had life-threatening autoimmune cytopenias and chronic mucocutaneous candidiasis. Naive lymphocytes from the affected patient displayed increased TH1 and follicular T helper cell and suppressed TH17cell responses. The mutation augmented cytokine-induced STAT1 phosphorylation without affecting dephosphorylation kinetics. Treatment with the Janus kinase 1/2 inhibitor ruxolitinib reduced hyperresponsiveness to type I and II interferons, normalized TH1 and follicular T helper cell responses, improved TH17 differentiation, cured mucocutaneous candidiasis, and maintained remission of immune-mediated cytopenias. Autoimmunity and infection caused by STAT1 GOF mutations are the result of dysregulated T helper cell responses. Janus kinase inhibitor therapy could represent an effective targeted treatment for long-term disease control in severely affected patients for whom hematopoietic stem cell transplantation is not available.