STAT1 Gain-of-Function Mutations Cause High Total STAT1 Levels With Normal Dephosphorylation

Immunophenotyping and Therapeutic Insights from Chronic Mucocutaneous Candidiasis Cases with STAT1 Gain-of-Function Mutations

PURPOSE

Heterozygous STAT1 Gain-of-Function (GOF) mutations are the most common cause of chronic mucocutaneous candidiasis (CMC) among Inborn Errors of Immunity. Clinically, these mutations manifest as a broad spectrum of immune dysregulation, including autoimmune diseases, vascular disorders, and malignancies. The pathogenic mechanisms of immune dysregulation and its impact on immune cells are not yet fully understood. In treatment, JAK inhibitors have shown therapeutic effectiveness in some patients.

METHODS

We analyzed clinical presentations, cellular phenotypes, and functional impacts in five Taiwanese patients with STAT1 GOF.

RESULTS

We identified two novel GOF mutations in 5 patients from 2 Taiwanese families, presenting with symptoms of CMC, late-onset rosacea, and autoimmunity. The enhanced phosphorylation and delayed dephosphorylation were displayed by the patients' cells. There are alterations in both innate and adaptive immune cells, including expansion of CD38+HLADR +CD8+ T cells, a skewed activated Tfh cells toward Th1, reduction of memory, marginal zone and anergic B cells, all main functional dendritic cell lineages, and a reduction in classical monocyte. Baricitinib showed therapeutic effectiveness without side effects.

CONCLUSION

Our study provides the first comprehensive clinical and molecular characteristics in STAT1 GOF patient in Taiwan and highlights the dysregulated T and B cells subsets which may hinge the autoimmunity in STAT1 GOF patients. It also demonstrated the therapeutic safety and efficacy of baricitinib in pediatric patient. Further research is needed to delineate how the aberrant STAT1 signaling lead to the changes in cellular populations as well as to better link to the clinical manifestations of the disease.

An improved SNAP-ADAR tool enables efficient RNA base editing to interfere with post-translational protein modification

RNA base editing relies on the introduction of adenosine-to-inosine changes into target RNAs in a highly programmable manner in order to repair disease-causing mutations. Here, we propose that RNA base editing could be broadly applied to perturb protein function by removal of regulatory phosphorylation and acetylation sites. We demonstrate the feasibility on more than 70 sites in various signaling proteins and identify key determinants for high editing efficiency and potent down-stream effects. For the JAK/STAT pathway, we demonstrate both, negative and positive regulation. To achieve high editing efficiency over a broad codon scope, we applied an improved version of the SNAP-ADAR tool. The transient nature of RNA base editing enables the comparably fast (hours to days), dose-dependent (thus partial) and reversible manipulation of regulatory sites, which is a key advantage over DNA (base) editing approaches. In summary, PTM interference might become a valuable field of application of RNA base editing.

Retrospective identification of the first cord blood-transplanted severe aplastic anemia in a STAT1-associated chronic mucocutaneous candidiasis family: case report, review of literature and pathophysiologic background

Severe aplastic anemia (SAA) is a life-threatening bone marrow failure syndrome whose development can be triggered by environmental, autoimmune, and/or genetic factors. The latter comprises germ line pathogenic variants in genes that bring about habitually predisposing syndromes as well as immune deficiencies that do so only occasionally. One of these disorders is the autosomal dominant form of chronic mucocutaneous candidiasis (CMC), which is defined by germ line STAT1 gain-of-function (GOF) pathogenic variants. The resultant overexpression and constitutive activation of STAT1 dysregulate the Janus kinase/signal transducer and activator of transcription 1 (STAT) signaling pathway, which normally organizes the development and proper interaction of different components of the immunologic and hematopoietic system. Although SAA is an extremely rare complication in this disorder, it gained a more widespread interest when it became clear that the underlying causative pathomechanism may, in a similar fashion, also be instrumental in at least some of the idiopathic SAA cases. Based on these premises, we present herein what is the historically most likely first cord blood-transplanted SAA case in a CMC family with a documented STAT1 GOF pathogenic variant. In addition, we recapitulate the characteristics of the six CMC SAA cases that have been reported so far and discuss the significance of STAT1 GOF pathogenic variants and other STAT1 signaling derangements in the context of these specific types of bone marrow failure syndromes. Because a constitutively activated STAT1 signaling, be it driven by STAT1 GOF germ line pathogenic variants or any other pathogenic variant-independent events, is apparently important for initiating and maintaining the SAA disease process, we propose to acknowledge that SAA is one of the definite disease manifestations in STAT1-mutated CMC cases. For the same reason, we deem it necessary to also incorporate molecular and functional analyses of STAT1 into the diagnostic work-up of SAA cases.

Targeting mitochondrial damage: shining a new light on immunotherapy

Mitochondrial damage has a particular impact on the immune system and tumor microenvironment, which can trigger cell stress, an inflammatory response, and disrupt immune cell function, thus all of which can accelerate the progression of the tumor. Therefore, it is of essence to comprehend how the immune system function and the tumor microenvironment interact with mitochondrial dysfunction for cancer treatment. Preserving the integrity of mitochondria or regulating the function of immune cells, such as macrophages, may enhance the efficacy of cancer therapy. Future research should concentrate on the interactions among mitochondria, the immune system, and the tumor microenvironment to identify new therapeutic strategies.

Mucocutaneous Candidiasis: Insights Into the Diagnosis and Treatment

Recent progress in the methods of genetic diagnosis of inborn errors of immunity has contributed to a better understanding of the pathogenesis of chronic mucocutaneous candidiasis (CMC) and potential therapeutic options. This review describes the latest advances in the understanding of the pathophysiology, diagnostic strategies, and management of chronic mucocutaneous candidiasis.

Ruxolitinib Improves Immune-Dysregulation Features but not Epigenetic Abnormality in a Patient with STAT1 GOF

PURPOSE

Patients with STAT1 gain-of-function (GOF) mutations often exhibit autoimmune features. The JAK1/2 inhibitor ruxolitinib can be administered to alleviate autoimmune symptoms; however, it is unclear how immune cells are molecularly changed by ruxolitinib treatment. Then, we aimed to investigate the trnscriptional and epigenetic status of immune cells before and after ruxolitinib treatment in a patient with STAT1 GOF.

METHODS

A patient with a heterozygous STAT1 GOF variant (p.Ala267Val), exhibiting autoimmune features, was treated with ruxolitinib, and peripheral blood mononuclear cells (PBMCs) were longitudinally collected. PBMCs were transcriptionally analyzed by single-cell cellular indexing of the transcriptomes and epitopes by sequencing (CITE-seq), and epigenetically analyzed by assay of transposase-accessible chromatin sequencing (ATAC-seq).

RESULTS

CITE-seq analysis revealed that before treatment, the patient's PBMCs exhibited aberrantly activated inflammatory features, especially IFN-related features. In particular, monocytes showed high expression levels of a subset of IFN-stimulated genes (ISGs). Ruxolitinib treatment substantially downregulated aberrantly overexpressed ISGs, and improved autoimmune features. However, epigenetic analysis demonstrated that genetic regions of ISGs-e.g., STAT1, IRF1, MX1, and OAS1-were highly accessible even after ruxolitinib treatment. When ruxolitinib was temporarily discontinued, the patient's autoimmune features were aggravated, which is in line with sustained epigenetic abnormality.

CONCLUSIONS

In a patient with STAT1 GOF, ruxolitinib treatment improved autoimmune features and downregulated aberrantly overexpressed ISGs, but did not correct epigenetic abnormality of ISGs.

Patients with STAT1 Gain-of-function Mutations Display Increased Apoptosis which is Reversed by the JAK Inhibitor Ruxolitinib

INTRODUCTION

The signal transducer and activator of transcription (STAT1) gain-of-function (GOF) syndrome accounts for most cases of chronic mucocutaneous candidiasis but is characterized by a broader clinical phenotype that may include bacterial, viral, or invasive fungal infections, autoimmunity, autoinflammatory manifestations, vascular complications, or malignancies. The severity of lymphopenia may vary and influence the infectious morbidity.

METHODS

In our cohort of seven STAT1-GOF patients, we investigated the mechanisms that may determine T lymphopenia, we characterized the interferon gene signature (IGS) and analyzed the effect of ruxolitinib in reverting the immune dysregulation.

RESULTS

STAT1-GOF patients exhibited increased T lymphocyte apoptosis that was significantly augmented in both resting conditions and following stimulation with mitogens and IFNα, as evaluated by flow cytometry by Annexin V/ Propidium iodide assay. The JAK inhibitor ruxolitinib significantly reduced the IFNα-induced hyperphosphorylation of STAT1 and reverted the stimulation-induced T-cell apoptosis, in vitro. In two adult STAT1-GOF patients, the JAKinib treatment ameliorated chronic mucocutaneous candidiasis and lymphopenia. Most STAT1-GOF patients, particularly those who had autoimmunity, presented increased IGS that significantly decreased in the two patients during ruxolitinib treatment.

CONCLUSION

In STAT1-GOF patients, T lymphocyte apoptosis is increased, and T lymphopenia may determine higher risk of severe infections. The JAKinib target therapy should be evaluated to treat severe chronic candidiasis and lymphopenia, and to downregulate the IFNs in patients with autoinflammatory or autoimmune manifestations.

Human STAT1 gain of function with chronic mucocutaneous candidiasis: A comprehensive review for strengthening the connection between bedside observations and laboratory research

Germline human heterozygous STAT1 gain-of-function (GOF) variants were first discovered a common cause of chronic mucocutaneous candidiasis (CMC) in 2011. Since then, numerous STAT1 GOF variants have been identified. A variety of clinical phenotypes, including fungal, viral, and bacterial infections, endocrine disorders, autoimmunity, malignancy, and aneurysms, have recently been revealed for STAT1 GOF variants, which has led to the expansion of the clinical spectrum associated with STAT1 GOF. Among this broad range of complications, it has been determined that invasive infections, aneurysms, and malignancies are poor prognostic factors for STAT1 GOF. The effectiveness of JAK inhibitors as a therapeutic option has been established, although further investigation of their long-term utility and side effects is needed. In contrast to the advancements in treatment options, the precise molecular mechanism underlying STAT1 GOF remains undetermined. Two primary hypotheses for this mechanism involve impaired STAT1 dephosphorylation and increased STAT1 protein levels, both of which are still controversial. A precise understanding of the molecular mechanism is essential for not only advancing diagnostics but also developing therapeutic interventions. Here, we provide a comprehensive review of STAT1 GOF with the aim of establishing a stronger connection between bedside observations and laboratory research.

JAK/STAT defects and immune dysregulation, and guiding therapeutic choices

Inborn errors of immunity (IEIs) encompass a diverse spectrum of genetic disorders that disrupt the intricate mechanisms of the immune system, leading to a variety of clinical manifestations. Traditionally associated with an increased susceptibility to recurrent infections, IEIs have unveiled a broader clinical landscape, encompassing immune dysregulation disorders characterized by autoimmunity, severe allergy, lymphoproliferation, and even malignancy. This review delves into the intricate interplay between IEIs and the JAK-STAT signaling pathway, a critical regulator of immune homeostasis. Mutations within this pathway can lead to a wide array of clinical presentations, even within the same gene. This heterogeneity poses a significant challenge, necessitating individually tailored therapeutic approaches to effectively manage the diverse manifestations of these disorders. Additionally, JAK-STAT pathway defects can lead to simultaneous susceptibility to both infection and immune dysregulation. JAK inhibitors, with their ability to suppress JAK-STAT signaling, have emerged as powerful tools in controlling immune dysregulation. However, questions remain regarding the optimal selection and dosing regimens for each specific condition. Hematopoietic stem cell transplantation (HSCT) holds promise as a curative therapy for many JAK-STAT pathway disorders, but this procedure carries significant risks. The use of JAK inhibitors as a bridge to HSCT has been proposed as a potential strategy to mitigate these risks.

Signal Transducer and Activator of Transcription Proteins at the Nexus of Immunodeficiency, Autoimmunity and Cancer

The signal transducer and activator of transcription (STAT) family of proteins has been demonstrated to perform pivotal roles downstream of a myriad of cytokines, particularly those that control immune cell production and function. This is highlighted by both gain-of-function (GOF) and loss-of-function (LOF) mutations being implicated in various diseases impacting cells of the immune system. These mutations are typically inherited, although somatic GOF mutations are commonly observed in certain immune cell malignancies. This review details the growing appreciation of STAT proteins as a key node linking immunodeficiency, autoimmunity and cancer.

Inferring gene regulatory network from single-cell transcriptomes with graph autoencoder model

The gene regulatory structure of cells involves not only the regulatory relationship between two genes, but also the cooperative associations of multiple genes. However, most gene regulatory network inference methods for single cell only focus on and infer the regulatory relationships of pairs of genes, ignoring the global regulatory structure which is crucial to identify the regulations in the complex biological systems. Here, we proposed a graph-based Deep learning model for Regulatory networks Inference among Genes (DeepRIG) from single-cell RNA-seq data. To learn the global regulatory structure, DeepRIG builds a prior regulatory graph by transforming the gene expression of data into the co-expression mode. Then it utilizes a graph autoencoder model to embed the global regulatory information contained in the graph into gene latent embeddings and to reconstruct the gene regulatory network. Extensive benchmarking results demonstrate that DeepRIG can accurately reconstruct the gene regulatory networks and outperform existing methods on multiple simulated networks and real-cell regulatory networks. Additionally, we applied DeepRIG to the samples of human peripheral blood mononuclear cells and triple-negative breast cancer, and presented that DeepRIG can provide accurate cell-type-specific gene regulatory networks inference and identify novel regulators of progression and inhibition.

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_H1-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

Introduction

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.

Methods

We generated Stat1T385M/+ mutant mice to model the immune impacts of STAT1 DBD GOF under specific-pathogen free (SPF) conditions.

Results

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.

Discussion

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.

JAKs and STATs from a Clinical Perspective: Loss-of-Function Mutations, Gain-of-Function Mutations, and Their Multidimensional Consequences

The JAK/STAT signaling pathway plays a key role in cytokine signaling and is involved in development, immunity, and tumorigenesis for nearly any cell. At first glance, the JAK/STAT signaling pathway appears to be straightforward. However, on closer examination, the factors influencing the JAK/STAT signaling activity, such as cytokine diversity, receptor profile, overlapping JAK and STAT specificity among non-redundant functions of the JAK/STAT complexes, positive regulators (e.g., cooperating transcription factors), and negative regulators (e.g., SOCS, PIAS, PTP), demonstrate the complexity of the pathway's architecture, which can be quickly disturbed by mutations. The JAK/STAT signaling pathway has been, and still is, subject of basic research and offers an enormous potential for the development of new methods of personalized medicine and thus the translation of basic molecular research into clinical practice beyond the use of JAK inhibitors. Gain-of-function and loss-of-function mutations in the three immunologically particularly relevant signal transducers STAT1, STAT3, and STAT6 as well as JAK1 and JAK3 present themselves through individual phenotypic clinical pictures. The established, traditional paradigm of loss-of-function mutations leading to immunodeficiency and gain-of-function mutation leading to autoimmunity breaks down and a more differentiated picture of disease patterns evolve. This review is intended to provide an overview of these specific syndromes from a clinical perspective and to summarize current findings on pathomechanism, symptoms, immunological features, and therapeutic options of STAT1, STAT3, STAT6, JAK1, and JAK3 loss-of-function and gain-of-function diseases.

The ups and downs of STAT3 function: too much, too little and human immune dysregulation

The STAT3 story has almost 30 years of evolving history. First identified in 1994 as a pro-inflammatory transcription factor, Signal Transducer and Activator of Transcription 3 (STAT3) has continued to be revealed as a quintessential pleiotropic signalling module spanning fields including infectious diseases, autoimmunity, vaccine responses, metabolism, and malignancy. In 2007, germline heterozygous dominant-negative loss-of-function variants in STAT3 were discovered as the most common cause for a triad of eczematoid dermatitis with recurrent skin and pulmonary infections, first described in 1966. This finding established that STAT3 plays a critical non-redundant role in immunity against some pathogens, as well as in the connective tissue, dental and musculoskeletal systems. Several years later, in 2014, heterozygous activating gain of function germline STAT3 variants were found to be causal for cases of early-onset multiorgan autoimmunity, thereby underpinning the notion that STAT3 function needed to be regulated to maintain immune homeostasis. As we and others continue to interrogate biochemical and cellular perturbations due to inborn errors in STAT3, we will review our current understanding of STAT3 function, mechanisms of disease pathogenesis, and future directions in this dynamic field.

Inborn errors of immunity with loss- and gain-of-function germline mutations in STAT1

STAT1 dysfunction causes a wide range of immune dysregulation phenotypes, which have been classified into four disease types, namely, (i) autosomal recessive (AR) complete STAT1 deficiency, (ii) AR partial STAT1 deficiency, (iii) autosomal dominant (AD) STAT1 deficiency, and (iv) AD STAT1 gain of function (GOF), based on their mode of inheritance and function. Disease types (i, ii, and iii) are caused by STAT1 loss-of-function (LOF) mutations, whereas disease type (iv) is caused by STAT1 GOF mutations. Therefore, the functional analysis of mutations is necessary for the precise diagnosis.

Inborn Errors of Immunity Causing Pediatric Susceptibility to Fungal Diseases

Inborn errors of immunity are a heterogeneous group of genetically determined disorders that compromise the immune system, predisposing patients to infections, autoinflammatory/autoimmunity syndromes, atopy/allergies, lymphoproliferative disorders, and/or malignancies. An emerging manifestation is susceptibility to fungal disease, caused by yeasts or moulds, in a superficial or invasive fashion. In this review, we describe recent advances in the field of inborn errors of immunity associated with increased susceptibility to fungal disease.

Unusual Talaromyces marneffei and Pneumocystis jirovecii coinfection in a child with a STAT1 mutation: A case report and literature review

Talaromyces marneffei and Pneumocystis jirovecii are the common opportunistic pathogens in immunodeficient patients. There have been no reports of T. marneffei and P. jirovecii coinfection in immunodeficient children. Signal transducer and activator of transcription 1 (STAT1) is a key transcription factor in immune responses. STAT1 mutations are predominately associated with chronic mucocutaneous candidiasis and invasive mycosis. We report a 1-year-2-month-old boy diagnosed with severe laryngitis and pneumonia caused by T. marneffei and P. jirovecii coinfection, which was confirmed by smear, culture, polymerase chain reaction and metagenome next-generation sequencing of bronchoalveolar lavage fluid. He has a known STAT1 mutation at amino acid 274 in the coiled-coil domain of STAT1 according to whole exome sequencing. Based on the pathogen results, itraconazole and trimethoprim-sulfamethoxazole were administered. This patient's condition improved, and he was discharged after two weeks of targeted therapy. In the one-year follow-up, the boy remained symptom-free without recurrence.

Tip of the iceberg: A comprehensive review of liver disease in Inborn errors of immunity

Inborn errors of immunity (IEIs) consist of numerous rare, inherited defects of the immune system that affect about 500,000 people in the United States. As advancements in diagnosis through genetic testing and treatment with targeted immunotherapy and bone marrow transplant emerge, increasing numbers of patients survive into adulthood posing fresh clinical challenges. A large spectrum of hepatobiliary diseases now present in those with immunodeficiency diseases, leading to morbidity and mortality in this population. Awareness of these hepatobiliary diseases has lagged the improved management of the underlying disorders, leading to missed opportunities to improve clinical outcomes. This review article provides a detailed description of specific liver diseases occurring in various inborn errors of immunity. A generalized approach to diagnosis and management of hepatic complications is provided, and collaboration with hepatologists, immunologists, and pathologists is emphasized as a requirement for optimizing management and outcomes.

Case report: A STAT1 gain-of-function mutation causes a syndrome of combined immunodeficiency, autoimmunity and pure red cell aplasia

Inherited autosomal dominant gain-of-function (GOF) mutations of signal transducer and activator of transcription 1 (STAT1) cause a wide range of symptoms affecting multiple systems, including chronic mucocutaneous candidiasis (CMC), infections, and autoimmune disorders. We describe a rare case of STAT1 mutation with recurrent CMC, lung infections, and anemia. According to the whole-exome sequencing (WES), the patient was genetically mutated in STAT1 GOF (c.854A>G, p.Q285R), and bone marrow biopsy suggested pure red cell aplasia (PRCA). As a functional verification, STAT1 levels and phosphorylation (p-STAT1) of peripheral blood mononuclear cells (PBMCs) following IFN-γ stimulation in STAT1 GOF patient was higher than in the healthy control. Combination therapy of blood transfusion, antimicrobials, intravenous immunoglobulin, methylprednisolone, and the Janus Kinase (JAK) specific inhibitor ruxolitinib was used during treatment of patients. The patient also received a hematopoietic stem cell transplant (HSCT) to help with infections and anemia. This is the first reported case of STAT1 GOF disease complicated with PRCA. This complication might be attributed to immune disorders caused by STAT1 GOF. Furthermore, ruxolitinib may be a viable therapeutic option before HSCT to improve disease management.

Detection of Neutralizing Anti-Type 1 Interferon Autoantibodies

Autoantibodies (autoAbs) that neutralize type 1 interferons (T1IFNs) are a major risk factor associated with developing critical COVID-19 disease and are most commonly found in individuals over age 70 and in patients with genetic or acquired thymic defects. Swift identification of autoAb-positive individuals may allow targeted interventions to prevent critical COVID-19 disease. Herein, we provide a workflow and protocols aimed at rapidly identifying individuals who are autoAb positive from a large cohort. Basic Protocol 1 describes a multiplex particle-based assay to screen large cohorts of individuals for binding levels of anti-T1IFN autoAbs, and Basic Protocol 2 describes a functional assay to test if autoAbs in patient plasma can block T1IFN-induced JAK/STAT signaling. © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Multiplex particle-based bead assay to screen for binding levels of anti-type 1 interferon autoantibodies Alternate Protocol: Multiplex particle-based bead assay to screen for binding levels of anti-type 1 interferon immunoglobulin subtypes and isotypes Support Protocol: Coupling type 1 interferons (IFN-α, IFN-β, and IFN-ω) to magnetic beads Basic Protocol 2: pSTAT1 functional assay to test for neutralization activity of anti-type 1 interferon autoantibodies.

Impact of JAK Inhibitors in Pediatric Patients with STAT1 Gain of Function (GOF) Mutations-10 Children and Review of the Literature

INTRODUCTION

Since the first description of gain of function (GOF) mutations in signal transducer and activator of transcription (STAT) 1, more than 300 patients have been described with a broad clinical phenotype including infections and severe immune dysregulation. Whilst Jak inhibitors (JAKinibs) have demonstrated benefits in several reported cases, their indications, dosing, and monitoring remain to be established.

METHODS

A retrospective, multicenter study recruiting pediatric patients with STAT1 GOF under JAKinib treatment was performed and, when applicable, compared with the available reports from the literature.

RESULTS

Ten children (median age 8.5 years (3-18), receiving JAKinibs (ruxolitinib (n = 9) and baricitinib (n = 1)) with a median follow-up of 18 months (2-42) from 6 inborn errors of immunity (IEI) reference centers were included. Clinical profile and JAKinib indications in our series were similar to the previously published 14 pediatric patients. 9/10 (our cohort) and 14/14 patients (previous reports) showed partial or complete responses. The median immune deficiency and dysregulation activity scores were 15.99 (5.2-40) pre and 7.55 (3-14.1) under therapy (p = 0.0078). Infection, considered a likely adverse event of JAKinib therapy, was observed in 1/10 patients; JAKinibs were stopped in 3/10 children, due to hepatotoxicity, pre-HSCT, and absence of response.

CONCLUSIONS

Our study supports the potentially beneficial use of JAKinibs in patients with STAT1 GOF, in line with previously published data. However, consensus regarding their indications and timing, dosing, treatment duration, and monitoring, as well as defining biomarkers to monitor clinical and immunological responses, remains to be determined, in form of international prospective multicenter studies using established IEI registries.

Ex vivo effect of JAK inhibition on JAK-STAT1 pathway hyperactivation in patients with dominant-negative STAT3 mutations

PURPOSE

STAT1 gain-of-function (GOF) and dominant-negative (DN) STAT3 syndromes share clinical manifestations including infectious and inflammatory manifestations. Targeted treatment with Janus-kinase (JAK) inhibitors shows promising results in treating STAT1 GOF-associated symptoms while management of DN STAT3 patients has been largely supportive. We here assessed the impact of ruxolitinib on the JAK-STAT1/3 pathway in DN STAT3 patients' cells.

METHODS

Using flow cytometry, immunoblot, qPCR, and ELISA techniques, we examined the levels of basal STAT1 and phosphorylated STAT1 (pSTAT1) of cells obtained from DN STAT3, STAT1 GOF patients, and healthy donors following stimulation with type I/II interferons (IFNs) or interleukin (IL)-6. We also describe the impact of ruxolitinib on cytokine-induced STAT1 signaling in these patients.

RESULTS

DN STAT3 and STAT1 GOF resulted in a similar phenotype characterized by increased STAT1 and pSTAT1 levels in response to IFNα (CD3⁺ cells) and IFNγ (CD14⁺ monocytes). STAT1-downstream gene expression and C-X-C motif chemokine 10 secretion were higher in most DN STAT3 patients upon stimulation compared to healthy controls. Ex vivo treatment with the JAK1/2-inhibitor ruxolitinib reduced cytokine responsiveness and normalized STAT1 phosphorylation in DN STAT3 and STAT1 GOF patient' cells. In addition, ex vivo treatment was effective in modulating STAT1 downstream signaling in DN STAT3 patients.

CONCLUSION

In the absence of effective targeted treatment options for AD-HIES at present, modulation of the JAK/STAT1 pathway with JAK inhibitors may be further explored particularly in those AD-HIES patients with autoimmune and/or autoinflammatory manifestations.

JAK inhibition in a patient with a STAT1 gain-of-function variant reveals STAT1 dysregulation as a common feature of aplastic anemia

BACKGROUND

Idiopathic aplastic anemia is a potentially lethal disease, characterized by T cell-mediated autoimmune attack of bone marrow hematopoietic stem cells. Standard of care therapies (stem cell transplantation or immunosuppression) are effective but associated with a risk of serious toxicities.

METHODS

An 18-year-old man presented with aplastic anemia in the context of a germline gain-of-function variant in STAT1. Treatment with the JAK1 inhibitor itacitinib resulted in a rapid resolution of aplastic anemia and a sustained recovery of hematopoiesis. Peripheral blood and bone marrow samples were compared before and after JAK1 inhibitor therapy.

FINDINGS

Following therapy, samples showed a decrease in the plasma concentration of interferon-γ, a decrease in PD1-positive exhausted CD8⁺ T cell population, and a decrease in an interferon responsive myeloid population. Single-cell analysis of chromatin accessibility showed decreased accessibility of STAT1 across CD4⁺ and CD8⁺ T cells, as well as CD14⁺ monocytes. To query whether other cases of aplastic anemia share a similar STAT1-mediated pathophysiology, we examined a cohort of 9 patients with idiopathic aplastic anemia. Bone marrow from six of nine patients also displayed abnormal STAT1 hyper-activation.

CONCLUSIONS

These findings raise the possibility that STAT1 hyperactivition defines a subset of idiopathic aplastic anemia patients for whom JAK inhibition may be an efficacious therapy.

FUNDING

Funding was provided by the Massachusetts General Hospital Department of Medicine Pathways Program and NIH T32 AI007387. A trial registration is at https://clinicaltrials.gov/ct2/show/NCT03906318.

DNA-Binding domain mutations confer severe outcome at an early age among STAT1 gain-of-function patients

BACKGROUND

STAT1 gain-of-function (GOF) is an immune dysregulatory disorder with poorly studied genotype-phenotype correlation, impeding prognostication and early intervention. Given previous mechanistic studies, as well as anecdotal clinical reports, we sought to systematically determine whether DNA-binding domain (DBD) mutations in STAT1 result in a different phenotype than mutations in other gene domains.

METHODS

Negative prognostic features previously identified by the International STAT1 GOF Study Group (invasive infections, intracranial aneurysms, and malignancy), as well as other clinical features and mortality, were compared within a cohort of 30 patients with STAT1 GOF diagnosed at our center, consisting of 9 patients with DBD mutations and 21 patients with non-DBD mutations. We subsequently re-analyzed mortality data from a large, previously-published 274-patient cohort by the International STAT1 GOF Study Group.

RESULTS

While no differences were noted with respect to malignancy or symptomatic aneurysms, invasive /opportunistic infections were substantially more common among DBD patients, as were sinopulmonary infections, bronchiectasis, enteropathy, endocrinopathies, lymphoproliferative manifestations, and recurrent fevers/HLH. DBD patients also had a lower probability of survival and younger age of mortality compared with non-DBD patients. Our re-evaluation of the published data from the International STAT1 GOF Study Group revealed a similar finding of earlier mortality among patients harboring DBD mutations.

CONCLUSION

We report that STAT1 GOF patients with DBD mutations may be regarded as a unique subgroup, impacted more by early-onset profound combined immunodeficiency and with earlier mortality. These findings may impact clinical decision making with respect to early intervention, and in particular hematopoietic stem cell transplant considerations, in such patients.

Chronic oral mucocutaneous candidiasis, recurrent respiratory infection, hepatosplenomegaly, and autoimmune diabetes mellitus: A case report of a gain-of-function mutation of STAT1 in a Chinese boy

BACKGROUND

Signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations are characterized by chronic mucocutaneous candidiasis and autoimmune diseases. Type 1 diabetes mellitus is one of the well-characterized autoimmune conditions.

CASE PRESENTATION

We reported a 5-year-old boy who presented with polydipsia and polyuria, with a medical history of chronic oral mucocutaneous candidiasis, recurrent respiratory infection, hepatosplenomegaly, and abnormal liver function. Genetic analysis identified a heterozygous GOF mutation (c.866A > G, p.Y289C) in STAT1.

RESULTS

Various medicines were given to the boy during the follow-up, including insulin to keep blood glucose stable, intravenous immunoglobulin and antifungal agents for recurrent infections, and antituberculosis drugs (isoniazid, rifampicin) to combat tuberculosis infection. He did not show recurrent infection, but chronic oral mucocutaneous candidiasis still occurred twice per month. The blood glucose level was well controlled.

CONCLUSION

This article illustrates that early diagnosis and identification of STAT1 mutation are essential for assessing the severity of the disease and determining reasonable treatment options.

Biallelic TRAF3IP2 variants causing chronic mucocutaneous candidiasis in a child harboring a STAT1 variant

BACKGROUND

Inherited chronic mucocutaneous candidiasis (CMC) is often caused by inborn errors of immunity, impairing the response to, or the production of IL-17A and IL-17F. About half of the cases carry STAT1 gain-of-function (GOF) mutations. Only few patients have been reported with mutations of TRAF3IP2, a gene encoding the adaptor ACT1 essential for IL-17 receptor(R) signaling. We investigated a 10-year-old girl with CMC, carrying a heterozygous variant of STAT1 and compound heterozygous variants of TRAF3IP2.

METHODS

By flow cytometry, STAT1 levels and phosphorylation (CD14+) as well as IL-17A, IL-22, IFN-γ, and IL-4 production (memory CD4⁺ T cells) were determined. ACT1 expression and binding to IL-17RA were assessed by Western blot and co-immunoprecipitation in HEK-293T cells transfected with plasmids encoding wild-type or mutant HA-tagged ACT1 and Flag-IL-17RA. We evaluated IL-17A responses by measuring luciferase induction under a NF-κB-driven reporter system in HEK-293T cells and Gro-α secretion in fibroblasts.

RESULTS

A STAT1 variant (c.1363G>A/p.V455I) was identified by next-generation sequencing and classified as likely non-pathogenic as functional testing revealed normal STAT1 expression and phosphorylation upon IFN-γ. We also found compound heterozygous variants (c.1325A>G/p.D451G and c.1335delA/p.K454fs11*) of TRAF3IP2. By overexpression, despite normal protein expression, and impaired (K454fs11*) or normal (D451G) interaction with IL-17RA, both mutant alleles resulted in impaired NF-κB activation. Patient's fibroblasts displayed abolished GRO-α secretion upon IL-17A stimulation. Finally, ex vivo CD4⁺ T cells showed increased IL-17A, IL-22, and IL-4 and normal low IFN-γ expression upon stimulation.

CONCLUSION

We identify novel compound heterozygous variants of TRAFP3IP2 causing autosomal recessive ACT1 deficiency in a child with CMC and provide a review of the current literature.

Functional analysis of two STAT1 gain-of-function mutations in two Iranian families with autosomal dominant chronic mucocutaneous candidiasis

Candidiasis is characterized by susceptibility to recurrent or persistent infections caused by Candida spp., typically Candida albicans, of cutaneous and mucosal surfaces. In this report, function and frequency of Th17 cells as well as genetics of patients susceptible to mucocutaneous candidiasis were studied. For patients, T-cell proliferation tests in response to Candida antigen, Th17 cell proportions, and STAT1 phosphorylation were evaluated through flow cytometry. Expression of IL17A, IL17F and IL22 genes were measured by real-time quantitative PCR. At the same time, whole exome sequencing was performed for all patients. We identified two heterozygous substitutions, one: c.821G > A (p. R274Q) was found in a multiplex family with three individuals affected, the second one: c.812A > C (p. Q271P) was found in a sporadic case. Both mutations are located in the coiled-coil domain (CCD) of STAT1. The frequency of Th17 cells, IL17A, IL17F, and IL22 gene expression in patients' peripheral blood mononuclear cells (PBMCs), and T-cell proliferation to Candida antigens were significantly reduced in the patients as compared to healthy controls. An increased STAT1 phosphorylation was observed in patients' PBMCs upon interferon (IFN)-γ stimulation as compared to healthy controls. We report two different but neighboring heterozygous mutations, located in exon 10 of the STAT1 gene, in four Iranian patients with CMC, one of whom also had hypothyroidism. These mutations were associated with impaired T cell proliferation to Candida antigen, low Th17 cell proportions, and increased STAT1 phosphorylation upon IFN-γ. We suggest that interfering with STAT1 phosphorylation might be a promising way for potential therapeutic measurements for such patients.

The New "Wholly Trinity" in the Diagnosis and Management of Inborn Errors of Immunity

The field of immunology has a rich and diverse history, and the study of inborn errors of immunity (IEIs) represents both the "cake" and the "icing on top of the cake," as it has enabled significant advances in our understanding of the human immune system. This explosion of knowledge has been facilitated by a unique partnership, a triumvirate formed by the physician who gathers detailed immunological and clinical phenotypic information from, and shares results with, the patient; the laboratory scientist/immunologist who performs diagnostic testing, as well as advanced functional correlative studies; and the genomics scientist/genetic counselor, who conducts and interprets varied genetic analyses, all of which are essential for dissecting constitutional genetic disorders. Although the basic principles of clinical care have not changed in recent years, the practice of clinical immunology has changed to reflect the prodigious advances in diagnostics, genomics, and therapeutics. An "omic/tics"-centric approach to IEI reflects the tremendous strides made in the field in the new millennium with recognition of new disorders, characterization of the molecular underpinnings, and development and implementation of personalized treatment strategies. This review brings renewed attention to bear on the indispensable "trinity" of phenotypic, genomic, and immunological analyses in the diagnosis, management, and treatment of IEIs.

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.

A Translational Investigation of IFN-α and STAT1 Signaling in Endothelial Cells during Septic Shock Provides Therapeutic Perspectives

Septic shock and disseminated intravascular coagulation (DIC) are known to be characterized by an endothelial cell dysfunction. The molecular mechanisms underlying this relationship are, however, poorly understood. In this work, we aimed to investigate human circulating IFN-α in patients with septic shock-induced DIC and tested the potential role of endothelial Stat1 (signal transducer and activator of transcription 1) as a therapeutic target in a mouse model of sepsis. For this, circulating type I, type II, and type III IFNs and procoagulant microvesicles were quantified in a prospective cohort of patients with septic shock. Next, we used a septic shock model induced by cecal ligation and puncture in wild-type mice, in Ifnar1 (type I IFN receptor subunit 1)-knockout mice, and in Stat1 conditional knockout mice. In human samples, we observed higher concentrations of circulating IFN-α and IFN-α1 in patients with DIC compared with patients without DIC, whereas concentrations of IFN-β, IFN-γ, IFN-λ1, IFN-λ2, and IFN-λ3 were not different. IFN-α concentration was positively correlated with CD105 microvesicle concentrations, reflecting endothelial injury. In Ifnar1^-/- mice, cecal ligation and puncture did not induce septic shock and was characterized by lesser endothelial cell injury, with lower aortic inflammatory cytokine expression, endothelial inflammatory-related gene expression, and fibrinolysis. In mice in which Stat1 was specifically ablated in endothelial cells, a marked protection against sepsis was also observed, suggesting the relevance of an endothelium-targeted strategy. Our work highlights the key roles of type I IFNs as pathogenic players in septic shock-induced DIC and the potential pertinence of endothelial STAT1 as a therapeutic target.

Chronic Mucocutaneous Candidiasis in Early Life: Insights Into Immune Mechanisms and Novel Targeted Therapies

Children with chronic mucocutaneous candidiasis (CMC) experience recurrent infections with Candida spp. Moreover, immune dysregulation in the early life of these patients induces various autoimmune diseases and affects normal growth and development. The adaptive and innate immune system components play a significant role in anti-fungal response. This response is mediated through IL-17 production by T helper cells. Inborn errors in IL-17-mediated pathways or Candida spp. sensing molecules are known to cause CMC. In this review, we describe underlying immune mechanisms of monogenic primary immune deficiency disorders known to cause CMC. We will explore insights into current management of these patients and novel available therapies.

Human STAT1 Gain-of-Function Heterozygous Mutations: Chronic Mucocutaneous Candidiasis and Type I Interferonopathy

Heterozygous gain-of-function (GOF) mutations in STAT1 in patients with chronic mucocutaneous candidiasis (CMC) and hypothyroidism were discovered in 2011. CMC is the recurrent or persistent mucocutaneous infection by Candida fungi, and hypothyroidism results from autoimmune thyroiditis. Patients with these diseases develop other infectious diseases, including viral, bacterial, and fungal diseases, and other autoimmune manifestations, including enterocolitis, immune cytopenia, endocrinopathies, and systemic lupus erythematosus. STAT1-GOF mutations are highly penetrant with a median age at onset of 1 year and often underlie an autosomal dominant trait. As many as 105 mutations at 72 residues, including 65 recurrent mutations, have already been reported in more than 400 patients worldwide. The GOF mechanism involves impaired dephosphorylation of STAT1 in the nucleus. Patient cells show enhanced STAT1-dependent responses to type I and II interferons (IFNs) and IL-27. This impairs Th17 cell development, which accounts for CMC. The pathogenesis of autoimmunity likely involves enhanced type I IFN responses, as in other type I interferonopathies. The pathogenesis of other infections, especially those caused by intramacrophagic bacteria and fungi, which are otherwise seen in patients with diminished type II IFN immunity, has remained mysterious. The cumulative survival rates of patients with and without severe disease (invasive infection, cancer, and/or symptomatic aneurysm) at 60 years of age are 31% and 87%, respectively. Severe autoimmunity also worsens the prognosis. The treatment of patients with STAT1-GOF mutations who suffer from severe infectious and autoimmune manifestations relies on hematopoietic stem cell transplantation and/or oral JAK inhibitors.

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.

Novel Gain-of-Function Mutation in Stat1 Sumoylation Site Leads to CMC/CID Phenotype Responsive to Ruxolitinib

Mutations in the coiled-coil and DNA-binding domains of STAT1 lead to delayed STAT1 dephosphorylation and subsequently gain-of-function. The associated clinical phenotype is broad and can include chronic mucocutaneous candidiasis (CMC) and/or combined immunodeficiency (CID). We report a case of CMC/CID in a 10-year-old boy due to a novel mutation in the small ubiquitin molecule (SUMO) consensus site at the C-terminal region of STAT1 leading to gain-of-function by impaired sumoylation. Immunodysregulatory features of disease improved after Janus kinase inhibitor (jakinib) treatment. Functional testing after treatment confirmed reversal of the STAT1 hyper-phosphorylation and downstream transcriptional activity. IL-17 and IL-22 production was, however, not restored with jakinib therapy (ruxolitinib), and the patient remained susceptible to opportunistic infection. In conclusion, a mutation in the SUMO consensus site of STAT1 can lead to gain-of-function that is reversible with jakinib treatment. However, full immunocompetence was not restored, suggesting that this treatment strategy might serve well as a bridge to definitive therapy such as hematopoietic stem cell transplant rather than a long-term treatment option.