Chronic mucocutaneous candidiasis caused by a gain-of-function mutation in the STAT1 DNA-binding domain

Therapy of traditional Chinese medicine in Candida spp. and Candida associated infections: A comprehensive review

Candida spp. are commonly a group of opportunistic dimorphic fungi, frequently causing diverse fungal infections in immunocompromised or immunosuppressant patients from mucosal disturbs (oropharyngeal candidiasis and vulvovaginal candidiasis) to disseminated infections (systemic candidiasis) with high morbidity and mortality. Importantly, several Candida species can be isolated from diseased individuals with digestive, neuropathic, respiratory, metabolic and autoimmune diseases. Due to increased resistance to conventional antifungal agents, the arsenal for antifungal purpose is in urgent need. Traditional Chinese Medicines (TCMs) are a huge treasury that can be used as promising candidates for antimycotic applications. In this review, we make a short survey of microbiological (morphology and virulence) and pathological (candidiasis and Candida related infections) features of and host immune response (innate and adaptive immunity) to Candida spp.. Based on the chemical structures and well-studied antifungal mechanisms, the monomers, extracts, decoctions, essential oils and other preparations of TCMs that are reported to have fair antifungal activities or immunomodulatory effects for anticandidal purpose are comprehensively reviewed. We also emphasize the importance of combination and drug pair of TCMs as useful anticandidal strategies, as well as network pharmacology and molecular docking as beneficial complements to current experimental approaches. This review construct a therapeutic module that can be helpful to guide in-future experimental and preclinical studies in the combat against fungal threats aroused by C. albicans and non-albicans Candida species.

STAT1 Mutations in Chronic Mucocutaneous Candidiasis Diagnosed in an Adult

A 30-year-old man presented with oral candidiasis and a history of lung abscess. He experienced recurring oral and skin candidiasis in childhood but spent long periods without any infections. Therefore, immunodeficiency was suspected. T and B lymphocyte and natural killer cell counts as well as immunoglobulin levels were normal. Human immunodeficiency virus test results were negative. Therefore, we suspected chronic mucocutaneous candidiasis (CMC). The signal transducer and activator of transcription (STAT) mutation, the leading cause of CMC, was detected by exome sequencing. Most cases of STAT1 mutations are diagnosed in childhood, but a few are diagnosed in adulthood because Candida infections may not be severe.

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.

Inborn Errors of Immunity and Cytokine Storm Syndromes

Inborn errors of immunity (IEI) are a diverse and growing category of more than 430 chronic disorders that share susceptibilities to infections. Whether the result of a genetic lesion that causes defective granule-dependent cytotoxicity, excessive lymphoproliferation, or an overwhelming infection represents a unique antigenic challenge, IEIs can display a proclivity for cytokine storm syndrome (CSS) development. This chapter provides an overview of CSS pathophysiology as it relates to IEIs. For each IEI, the immunologic defect and how it promotes or discourages CSS phenomena are reviewed. The IEI-associated molecular defects in pathways that are postulated to be critical to CSS physiology (i.e., toll-like receptors, T regulatory cells, the IL-12/IFNγ axis, IL-6) and, whenever possible, review strategies for treating CSS in IEI patients with molecularly directed therapies are highlighted.

Next generation sequencing (NGS)-based approach to diagnosing Algerian patients with suspected inborn errors of immunity (IEIs)

The advent of next-generation sequencing (NGS) technologies has greatly expanded our understanding of both the clinical spectra and genetic landscape of inborn errors of immunity (IEIs). Endogamous populations may be enriched for unique, ancestry-specific disease-causing variants, a consideration that significantly impacts molecular testing and analysis strategies. Herein, we report on the application of a 2-step NGS-based testing approach beginning with targeted gene panels (TGPs) tailored to specific IEI subtypes and reflexing to whole exome sequencing (WES) if negative for Northwest Algerian patients with suspected IEIs. Our overall diagnostic yield of 57% is comparable to others broadly applying short-read NGS to IEI detection, but data from our localized cohort show some similarities and differences from NGS studies performed on larger regional IEI cohorts. This suggests the importance of tailoring diagnostic strategies to local demographics and needs, but also highlights ongoing concerns inherent to the application of genomics for clinical IEI diagnostics.

A novel interface between the N-terminal and coiled-coil domain of STAT1 functions in an auto-inhibitory manner

BACKGROUND

STAT1 is an intracellular signaling molecule that is crucially involved in the regulation of the innate immune system by activation of defense mechanisms against microbial pathogens. Phosphorylation-dependent activation of the STAT1 transcription factor is associated with a conversion from an antiparallel to parallel dimer configuration, which after nuclear import binds to DNA. However, not much is known about the specific intermolecular interactions that stabilize unphosphorylated, antiparallel STAT1 complexes prior to activation.

RESULTS

In this study, we identified a previously unknown interdimeric interaction site, which is involved in the termination of STAT1 signaling. Introduction of the glutamic acid-to-alanine point mutation E169A in the coiled-coil domain (CCD) by site-directed mutagenesis led to increased tyrosine phosphorylation as well as accelerated and prolonged nuclear accumulation in transiently transfected cells. In addition, DNA-binding affinity and transcriptional activity were strongly enhanced in the substitution mutant compared to the wild-type (WT) protein. Furthermore, we have demonstrated that the E169 residue in the CCD mediates the release of the dimer from the DNA in an auto-inhibitory manner.

CONCLUSION

Based on these findings, we propose a novel mechanism for the inactivation of the STAT1 signaling pathway, assigning the interface with the glutamic acid residue 169 in the CCD a crucial role in this process. Video Abstract.

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.

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.

Fungal diseases: Oral dysbiosis in susceptible hosts

The oral cavity is colonized by a large number of microorganisms that are referred to collectively as the oral microbiota. These indigenous microorganisms have evolved in symbiotic relationships with the oral mucosal immune system and are involved in maintaining homeostasis in the oral cavity. Although Candida species are commonly found in the healthy oral cavity without causing infection, these fungi can become pathogenic. Recents advances indicate that the development of oral candidiasis is driven both by Candida albicans overgrowth in a dysbiotic microbiome and by disturbances in the host's immune system. Perturbation of the oral microbiota triggered by host-extrinsic (ie, medications), host-intrinsic (ie, host genetics), and microbiome-intrinsic (ie, microbial interactions) factors may increase the risk of oral candidiasis. In this review, we provide an overview of the oral mycobiome, with a particular focus on the interactions of Candida albicans with some of the most common oral bacteria and the oral mucosal immune system. Also, we present a summary of our current knowledge of the host-intrinsic and host-extrinsic factors that can predispose to oral candidiasis.

Genetic Analysis of a Cohort of 275 Patients with Hyper-IgE Syndromes and/or Chronic Mucocutaneous Candidiasis

Hyper-IgE syndromes and chronic mucocutaneous candidiasis constitute rare primary immunodeficiency syndromes with an overlapping clinical phenotype. In recent years, a growing number of underlying genetic defects have been identified. To characterize the underlying genetic defects in a large international cohort of 275 patients, of whom 211 had been clinically diagnosed with hyper-IgE syndrome and 64 with chronic mucocutaneous candidiasis, targeted panel sequencing was performed, relying on Agilent HaloPlex and Illumina MiSeq technologies. The targeted panel sequencing approach allowed us to identify 87 (32 novel and 55 previously described) mutations in 78 patients, which generated a diagnostic success rate of 28.4%. Specifically, mutations in DOCK8 (26 patients), STAT3 (21), STAT1 (15), CARD9 (6), AIRE (3), IL17RA (2), SPINK5 (3), ZNF341 (2), CARMIL2/RLTPR (1), IL12RB1 (1), and WAS (1) have been detected. The most common clinical findings in this cohort were elevated IgE (81.5%), eczema (71.7%), and eosinophilia (62.9%). Regarding infections, 54.7% of patients had a history of radiologically proven pneumonia, and 28.3% have had other serious infections. History of fungal infection was noted in 53% of cases and skin abscesses in 52.9%. Skeletal or dental abnormalities were observed in 46.2% of patients with a characteristic face being the most commonly reported feature (23.1%), followed by retained primary teeth in 18.9% of patients. Targeted panel sequencing provides a cost-effective first-line genetic screening method which allows for the identification of mutations also in patients with atypical clinical presentations and should be routinely implemented in referral centers.

Inborn errors of STAT1 immunity

Signal transducer and activator of transcription 1 (STAT1) is a latent cytoplasmic transcription factor that is activated by multiple stimuli, including type I, II, and III interferons and interleukin-27. Inborn errors of human STAT1 immunity underlie 4 distinct disorders: autosomal recessive (AR) complete STAT1 deficiency, AR partial STAT1 deficiency, autosomal dominant (AD) STAT1 deficiency, and AD STAT1 gain-of-function. Each disease presents distinct clinical manifestations, excluding the difference in two AR STAT1 deficiencies, which are mainly explained by severity. This observation reflects the multiple and complex roles of STAT1 and how STAT1-mediated signaling is finely tuned in host immune systems.

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.

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.

Clinical, Immunological, and Genetic Features in Patients with Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) and IPEX-like Syndrome

BACKGROUND

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inborn error of immunity caused by mutations in the forkhead box P3 (FOXP3) gene.

OBJECTIVE

In this study, we conducted a systematic review of patients with IPEX and IPEX-like syndrome to delineate differences in these 2 major groups.

METHODS

The literature search was performed in PubMed, Web of Science, and Scopus databases, and demographic, clinical, immunologic, and molecular data were compared between the IPEX and IPEX-like groups.

RESULTS

A total of 459 patients were reported in 148 eligible articles. Major clinical differences between patients with IPEX and IPEX-like syndrome were observed in rates of pneumonia (11% vs 31%, P < .001), bronchiectasis (0.3% vs 14%, P < .001), diarrhea (56% vs 42%, P = .020), and organomegaly (10% vs 23%, P = .001), respectively. Eosinophilia (95% vs 100%), low regulatory T-cell count (68% vs 50%), and elevated IgE (87% vs 61%) were the most prominent laboratory findings in patients with IPEX and IPEX-like syndrome, respectively. In the IPEX group, a lower mortality rate was observed among patients receiving hematopoietic stem cell transplantation (HSCT) (24%) compared with other patients (43%), P = .008; however, in the IPEX-like group, it was not significant (P = .189).

CONCLUSIONS

Patients with IPEX syndrome generally suffer from enteropathy, autoimmunity, dermatitis, eosinophilia, and elevated serum IgE. Despite similarities in their clinical presentations, patients with IPEX-like syndrome are more likely to present common variable immunodeficiency-like phenotype such as respiratory tract infections, bronchiectasis, and organomegaly. HSCT is currently the only curative therapy for both IPEX and IPEX-like syndrome and may result in favorable outcome.

Cryptococcal pneumonia in an adolescent with a gain-of-function variant in signal transduction and activator of transcription 1 (STAT1)

An adolescent male with a history of autoimmune enteropathy, autoimmune hypothyroidism, aphthous stomatitis and recurrent oral Candida infections only in the setting of curative antibiotic courses presented with cryptococcal pneumonia and perihilar adenitis, which was successfully treated with antifungal therapy. The patient had a complex history with several immunological anomalies. Whole exome sequencing revealed a known STAT1 pathogenic variant, associated with gain of function (GOF). This case expands our understanding of the broad clinical phenotype manifested by STAT1 GOF and emphasises the importance of consideration of this diagnosis in patients presenting with opportunistic infections and autoimmunity.

Gene analysis of seven cases of primary immunodeficiency

BACKGROUND

Primary immune deficiency diseases (PID) are a group of potentially serious disorders in which inherited defects in the immune system lead to increased infections. This paper explores the clinical characteristics and pathogenic gene mutation of PID.

METHODS

The clinical data, clinical manifestations, and gene sequencing results of seven children were analyzed.

RESULTS

Among the seven children, six were male, and one was female, aged from 4 months to 13 years old. All of them had a history of repeated infection and pneumonia. High throughput sequencing (NGS) showed that the BTK gene of case 1 had c.1921c > t mutation; the BTK gene of case 2 had c.906-908del splice site mutation; the BTK gene of case 3 had c.718delg mutation; the cybb gene of case 4 had c.469c > t mutation; the IL2RG gene of case 5 had c.202g > A mutation; the STAT1 gene of case 6 had c.854a > G mutation; the case 7 had c.718delg mutation. There was c.1154c > t mutation in the STAT1 gene. Cases 1, 3, 6 and 7 were new mutations, and cases 2, 4, and 5 were inherited from mothers.

CONCLUSIONS

In clinical cases of children with recurrent infection, the immunologic index is abnormal, so we need to be highly aware of the possibility of PID, and timely high-throughput sequencing is helpful for the diagnosis.

Molecular mechanism of azoles resistant Candida albicans in a patient with chronic mucocutaneous candidiasis

BACKGROUND

More and more azole-resistant strains emerged through the development of acquired resistance and an epidemiological shift towards inherently less susceptible species. The mechanisms of azoles resistance of Candida albicans is very complicated. In this study, we aim to investigate the mechanism of azole-resistant C. albicans isolated from the oral cavity of a patient with chronic mucocutaneous candidiasis (CMC).

CASE PRESENTATION

CMC diagnosis was given based on clinical manifestations, laboratory test findings and gene sequencing technique. Minimum inhibitory concentration (MIC) of the fungal isolate, obtained from oral cavity termed as CA-R, was obtained by in vitro anti-fungal drugs susceptibility test. To further investigate the resistant mechanisms, we verified the mutations of drug target genes (i.e. ERG11 and ERG3) by Sanger sequencing, and verified the over-expression of ERG11 and drug efflux genes (i.e. CDR1 and CDR2) by RT-PCR. A heterozygous mutation of c.1162A > G resulting in p.K388E was detected in STAT1 of the patient. The expression of CDR1 and CDR2 in CA-R was 4.28-fold and 5.25-fold higher than that of type strain SC5314, respectively.

CONCLUSIONS

Up-regulation of CDR1 and CDR2 was mainly responsible for the resistance of CA-R. For CMC or other immunodeficiency patients, drug resistance monitoring is necessary.

Human gain-of-function STAT1 mutation disturbs IL-17 immunity in mice

Gain-of-function (GOF) mutations in the gene for signal transducer and activator of transcription 1 (STAT1) account for approximately one-half of patients with chronic mucocutaneous candidiasis (CMC) disease. Patients with GOF-STAT1 mutations display a broad variety of infectious and autoimmune manifestations in addition to CMC, and those with severe infections and/or autoimmunity have a poor prognosis. The establishment of safe and effective treatments based on a precise understanding of the molecular mechanisms of this disorder is required to improve patient care. To tackle this problem, we introduced the human R274Q GOF mutation into mice [GOF-Stat1 knock-in (GOF-Stat1R274Q)]. To investigate the immune responses, we focused on the small intestine (SI), which contains abundant Th17 cells. Stat1R274Q/R274Q mice showed excess phosphorylation of STAT1 in CD4+ T cells upon IFN-γ stimulation, consistent with the human phenotype in patients with the R274Q mutation. We identified two subpopulations of CD4+ T cells, those with ‘normal’ or ‘high’ level of basal STAT1 protein in Stat1R274Q/R274Q mice. Upon IFN-γ stimulation, the ‘normal’ level CD4+ T cells were more efficiently phosphorylated than those from WT mice, whereas the ‘high’ level CD4+ T cells were not, suggesting that the level of STAT1 protein does not directly correlate with the level of pSTAT1 in the SI. Inoculation of Stat1R274Q/R274Q mice with Candida albicans elicited decreased IL-17-producing CD4+RORγt+ cells. Stat1R274Q/R274Q mice also excreted larger amounts of C. albicans DNA in their feces than control mice. Under these conditions, there was up-regulation of T-bet in CD4+ T cells. GOF-Stat1R274Q mice thus should be a valuable model for functional analysis of this disorder.

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.

A Human STAT1 Gain-of-Function Mutation Impairs CD8+ T Cell Responses against Gammaherpesvirus 68

Autosomal dominant STAT1 mutations in humans have been associated with chronic mucocutaneous candidiasis (CMC), as well as with increased susceptibility to herpesvirus infections. Prior studies have focused on mucosal and Th17-mediated immunity against Candida, but mechanisms of impaired antiviral immunity have not previously been examined. To begin to explore the mechanisms of STAT1-associated immunodeficiency against herpesviruses, we generated heterozygous STAT1 R274W knock-in mice that have a frequently reported STAT1 mutation associated in humans with susceptibility to herpesvirus infections. In primary macrophages and fibroblasts, we found that STAT1 R274W had no appreciable effect on cell-intrinsic immunity against herpes simplex virus 1 (HSV-1) or gammaherpesvirus 68 (γHV68) infection. However, intraperitoneal inoculation of mice with γHV68 was associated with impaired control of infection at day 14 in STAT1 R274W mice compared with that in wild-type (WT) littermate control animals. Infection of STAT1 R274W mice was associated with paradoxically decreased expression of IFN-stimulated genes (ISGs) and gamma interferon (IFN-γ), likely secondary to defective CD4⁺ and CD8⁺ T cell responses, including diminished numbers of antigen-specific CD8⁺ T cells. Viral pathogenesis studies in WT and STAT1 R274W mixed bone marrow chimeric mice revealed that the presence of WT leukocytes was sufficient to limit infection and that antigen-specific STAT1 R274W CD8⁺ T cell responses were impaired even in the presence of WT leukocytes. Thus, in addition to regulating Th17 responses against Candida, a STAT1 gain-of-function mutant impedes antigen-specific T cell responses against a common gammaherpesvirus in mice.IMPORTANCE Mechanisms of immunodeficiency related to STAT1 gain of function have not been previously studied in an animal model of viral pathogenesis. Using virological and immunological techniques, we examined the immune response to γHV68 in heterozygous mice that have an autosomal dominant mutation in the STAT1 coiled-coil domain (STAT1 R274W). We observed impaired control of infection, which was associated with diminished production of gamma interferon (IFN-γ), fewer effector CD4⁺ and CD8⁺ T cells, and a reduction in the number of antigen-specific CD8⁺ T cells. These findings indicate that a STAT1 gain-of-function mutation limits production of antiviral T cells, likely contributing to immunodeficiency against herpesviruses.

IRF and STAT Transcription Factors - From Basic Biology to Roles in Infection, Protective Immunity, and Primary Immunodeficiencies

The induction and action of type I interferon (IFN) is of fundamental importance in human immune defenses toward microbial pathogens, particularly viruses. Basic discoveries within the molecular and cellular signaling pathways regulating type I IFN induction and downstream actions have shown the essential role of the IFN regulatory factor (IRF) and the signal transducer and activator of transcription (STAT) families, respectively. However, the exact biological and immunological functions of these factors have been most clearly revealed through the study of inborn errors of immunity and the resultant infectious phenotypes in humans. The spectrum of human inborn errors of immunity caused by mutations in IRFs and STATs has proven very diverse. These diseases encompass herpes simplex encephalitis (HSE) and severe influenza in IRF3- and IRF7/IRF9 deficiency, respectively. They also include Mendelian susceptibility to mycobacterial infection (MSMD) in STAT1 deficiency, through disseminated measles infection associated with STAT2 deficiency, and finally staphylococcal abscesses and chronic mucocutaneous candidiasis (CMC) classically described with Hyper-IgE syndrome (HIES) in the case of STAT3 deficiency. More recently, increasing focus has been on aspects of autoimmunity and autoinflammation playing an important part in many primary immunodeficiency diseases (PID)s, as exemplified by STAT1 gain-of-function causing CMC and autoimmune thyroiditis, as well as a recently described autoinflammatory syndrome with hypogammaglobulinemia and lymphoproliferation as a result of STAT3 gain-of-function. Here I review the infectious, inflammatory, and autoimmune disorders arising from mutations in IRF and STAT transcription factors in humans, highlightning the underlying molecular mechanisms and immunopathogenesis as well as the clinical/therapeutic perspectives of these new insights.

Clinical, Immunological, and Molecular Heterogeneity of 173 Patients With the Phenotype of Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-Linked (IPEX) Syndrome

Background: Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) Syndrome is a rare recessive disorder caused by mutations in the FOXP3 gene. In addition, there has been an increasing number of patients with wild-type FOXP3 gene and, in some cases, mutations in other immune regulatory genes. Objective: To molecularly asses a cohort of 173 patients with the IPEX phenotype and to delineate the relationship between the clinical/immunologic phenotypes and the genotypes. Methods: We reviewed the clinical presentation and laboratory characteristics of each patient and compared clinical and laboratory data of FOXP3 mutation-positive (IPEX patients) with those from FOXP3 mutation-negative patients (IPEX-like). A total of 173 affected patients underwent direct sequence analysis of the FOXP3 gene while 85 IPEX-like patients with normal FOXP3 were investigated by a multiplex panel of "Primary Immune Deficiency (PID-related) genes." Results: Forty-four distinct FOXP3 variants were identified in 88 IPEX patients, 9 of which were not previously reported. Among the 85 IPEX-like patients, 19 different disease-associated variants affecting 9 distinct genes were identified. Conclusions: We provide a comprehensive analysis of the clinical features and molecular bases of IPEX and IPEX-like patients. Although we were not able to identify major distinctive clinical features to differentiate IPEX from IPEX-like syndromes, we propose a simple flow-chart to effectively evaluate such patients and to focus on the most likely molecular diagnosis. Given the large number of potential candidate genes and overlapping phenotypes, selecting a panel of PID-related genes will facilitate a molecular diagnosis.

Bacille Calmette-Guerin Complications in Newly Described Primary Immunodeficiency Diseases: 2010-2017

Bacille Calmette–Guerin (BCG) vaccine is widely used as a prevention strategy against tuberculosis. BCG is a live vaccine, usually given early in life in most countries. While safe to most recipients, it poses a risk to immunocompromised patients. Several primary immunodeficiency diseases (PIDD) have been classically associated with complications related to BCG vaccine. However, a number of new inborn errors of immunity have been described lately in which little is known about adverse reactions following BCG vaccination. The aim of this review is to summarize the existing data on BCG-related complications in patients diagnosed with PIDD described since 2010. When BCG vaccination status or complications were not specifically addressed in those manuscripts, we directly contacted the corresponding authors for further clarification. We also analyzed data on other mycobacterial infections in these patients. Based on our analysis, around 8% of patients with gain-of-function mutations in STAT1 had mycobacterial infections, including localized complications in 3 and disseminated disease in 4 out of 19 BCG-vaccinated patients. Localized BCG reactions were also frequent in activated PI3Kδ syndrome type 1 (3/10) and type 2 (2/18) vaccinated children. Also, of note, no BCG-related complications have been described in either CTLA4 or LRBA protein-deficient patients; and not enough information on BCG-vaccinated NFKB1 or NFKB2-deficient patients was available to drive any conclusions about these diseases. Despite the high prevalence of environmental mycobacterial infections in GATA2-deficient patients, only one case of BCG reaction has been reported in a patient who developed disseminated disease. In conclusion, BCG complications could be expected in some particular, recently described PIDD and it remains a preventable risk factor for pediatric PIDD patients.

Chronic mucocutaneous candidiasis due to gain-of-function mutation in STAT1

Chronic mucocutaneous candidiasis (CMC) is a heterogenous group of primary immunodeficiency diseases characterised by susceptibility to chronic or recurrent superficial Candida infection of skin, nails and mucous membranes. Gain-of-function mutations in the STAT1 gene (STAT1-GOF) are the most common genetic aetiology for CMC, and mutation analysis should be considered. These mutations lead to defective responses in Type 1 and Type 17 helper T cells (Th1 and Th17), which, depending on the mutation, also predispose to infection with Staphylococci, Mycobacteria and Herpesviridae. We describe the clinical and genetic findings for three patients with CMC due to gain-of-function mutations in the STAT1 gene.

Disseminated Tuberculosis and Chronic Mucocutaneous Candidiasis in a Patient with a Gain-of-Function Mutation in Signal Transduction and Activator of Transcription 1

In humans, recessive loss-of-function mutations in STAT1 are associated with mycobacterial and viral infections, whereas gain-of-function (GOF) mutations in STAT1 are associated with a type of primary immunodeficiency related mainly, but not exclusively, to chronic mucocutaneous candidiasis (CMC). We studied and established a molecular diagnosis in a pediatric patient with mycobacterial infections, associated with CMC. The patient, daughter of a non-consanguineous mestizo Mexican family, had axillary adenitis secondary to BCG vaccination and was cured with resection of the abscess at 1-year old. At the age of 4 years, she had a supraclavicular abscess with acid-fast-staining bacilli identified in the soft tissue and bone, with clinical signs of disseminated infection and a positive Gene-X-pert test, which responded to anti-mycobacterial drugs. Laboratory tests of the IL-12/interferon gamma (IFN-γ) circuit showed a higher production of IL-12p70 in the whole blood from the patient compared to healthy controls, when stimulated with BCG and BCG + IFN-γ. The whole blood of the patient produced 35% less IFN-γ compared to controls assessed by ELISA and flow cytometry, but IL-17 producing T cells from patient were almost absent in PBMC stimulated with PMA plus ionomycin. Signal transduction and activator of transcription 1 (STAT1) was hyperphosphorylated at tyrosine 701 in response to IFN-γ and -α, as demonstrated by flow cytometry and Western blotting in fresh blood mononuclear cells and in Epstein-Barr virus lymphoblastoid cell lines (EBV-LCLs); phosphorylation of STAT1 in EBV-LCLs from the patient was resistant to inhibition by staurosporine but sensitive to ruxolitinib, a Jak phosphorylation inhibitor. Genomic DNA sequencing showed a de novo mutation in STAT1 in cells from the patient, absent in her parents and brother; a known T385M missense mutation in the DNA-binding domain of the transcription factor was identified, and it is a GOF mutation. Therefore, GOF mutations in STAT1 can induce susceptibility not only to fungal but also to mycobacterial infections by mechanisms to be determined.

Gain-of-Function Mutations in STAT1: A Recently Defined Cause for Chronic Mucocutaneous Candidiasis Disease Mimicking Combined Immunodeficiencies

Chronic Mucocutaneous Candidiasis (CMC) is the chronic, recurrent, noninvasive Candida infections of the skin, mucous membranes, and nails. A 26-month-old girl was admitted with the complaints of recurrent oral Candidiasis, diarrhea, and respiratory infections. Candida albicans grew in oral mucosa swab. CMV and EBV DNA titers were elevated. She had hypergammaglobulinemia; IgE level, percentages of lymphocyte subgroups, and in vitro T-cell proliferation responses were normal. She had parenchymal nodules within the lungs and a calcific nodule in the liver. Chronic-recurrent infections with different pathogens leading to significant morbidity suggested combined immunodeficiency, CMC, or Mendelian susceptibility to mycobacterial diseases. Genetic analysis revealed a predefined heterozygous gain-of-function mutation (GOF) (c.1154 C>T, p.Thr385Met) in the gene coding STAT1 molecule. Hematopoietic stem cell transplantation (HSCT) was planned because of severe recurring infections. Patients with STAT1 GOF mutations may exhibit diverse phenotypes including infectious and noninfectious findings. HSCT should be considered as an early treatment option before permanent organ damage leading to morbidity and mortality develops. This case is presented to prompt clinicians to consider STAT1 GOF mutations in the differential diagnosis of patients with chronic Candidiasis and recurrent infections with multiple organisms, since these mutations are responsible for nearly half of CMC cases reported.

Chronic mucocutaneous candidiasis: what can we conclude about IL-17 antagonism?

PURPOSE

IL-17 antagonists are effective for psoriasis in clinical trials, but long-term safety is not fully characterized. Since chronic mucocutaneous candidiasis (CMC) is caused by defects in the IL-17 pathway, CMC risk data have been touted as providing reassurance about the safety of IL-17 antagonism.

METHODS

We performed a literature review to identify patients with CMC and compared the prevalence of cancer in these patients to the reported 5-year prevalence.

RESULTS

There was a higher prevalence of oropharyngeal (2.5% vs. 0.028%; p < .0001) and esophageal cancer (1.9% vs. 0.013%; p < .0001) in patients with CMC. There were no reports of cancer in 31 patients with CMC caused by an isolated IL-17 deficiency (IL-17F, IL-17RA, IL17RC); however, a study would need over 1000 patients to detect even a 10-fold increase in the most common malignancy of CMC patients.

CONCLUSIONS

There is evidence that some forms of CMC are associated with an increase in cancer. While CMC is heterogeneous, our findings suggest that we cannot use CMC data to reassure patients on the long-term safety of IL-17 antagonists beyond the safety results from clinical trials, and perhaps caution should be taken with the development of candidiasis in patients taking these medications.

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

BACKGROUND

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.

OBJECTIVE

We sought to investigate NK cell function in patients with STAT1 GOF mutations.

METHODS

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 in vitro with ruxolitinib.

RESULTS

Peripheral blood NK cells from patients with STAT1 GOF mutations had impaired terminal maturation. Specifically, patients with STAT1 GOF mutations have immature CD56^dim 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 in vitro and in vivo restored perforin expression in CD56^dim NK cells and partially restored NK cell cytotoxic function.

CONCLUSIONS

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.

T-bet, but not Gata3, overexpression is detrimental in a neurotropic viral infection

Intracerebral Theiler's murine encephalomyelitis virus (TMEV) infection in mice induces inflammatory demyelination in the central nervous system. Although C57BL/6 mice normally resistant to TMEV infection with viral clearance, we have previously demonstrated that RORγt-transgenic (tg) C57BL/6 mice, which have Th17-biased responses due to RORγt overexpression in T cells, became susceptible to TMEV infection with viral persistence. Here, using T-bet-tg C57BL/6 mice and Gata3-tg C57BL/6 mice, we demonstrated that overexpression of T-bet, but not Gata3, in T cells was detrimental in TMEV infection. Unexpectedly, T-bet-tg mice died 2 to 3 weeks after infection due to failure of viral clearance. Here, TMEV infection induced splenic T cell depletion, which was associated with lower anti-viral antibody and T cell responses. In contrast, Gata3-tg mice remained resistant, while Gata3-tg mice had lower IFN-γ and higher IL-4 production with increased anti-viral IgG1 responses. Thus, our data identify how overexpression of T-bet and Gata3 in T cells alters anti-viral immunity and confers susceptibility to TMEV infection.

A gain-of-function mutation of STAT1: A novel genetic factor contributing to chronic mucocutaneous candidiasis

Heterozygous gain-of-function (GOF) mutations in the signal transducer and activator of transcription 1 (STAT1) have increasingly been identified as a genetic cause of autosomal-dominant (AD) chronic mucocutaneous candidiasis (CMC). In this article, we describe a 33-year-old man who experienced chronic refractory candidiasis, recurrent otitis media, and pneumonia resulting in bronchiectasis, severe oral and esophageal candidiases with strictures associated with hypothyroidism and immune hemolytic anemia. His son also suffered from persistent candidiasis, chronic diarrhea, poor weight gain, and pneumonia that resulted in his demise because of sepsis. The immunological workup showed that an inverse CD4/CD8 ratio and serum immunoglobulins were all within normal ranges. The laboratory data revealed failure in response to Candida lymphocyte transformation test. In addition, by Sanger sequencing method, we found a heterozygous mutation, Thr385Met (T385M), located in the DNA-binding domain of STAT1, which was previously shown to be GOF. These findings illustrate the broad and variable clinical phenotype of heterozygous STAT1 GOF mutations. However, more clinical information and phenotype-genotype studies are required to define the clinical phenotype caused by AD STAT1 GOF.

Autosomal dominant gain of function STAT1 mutation and severe bronchiectasis

BACKGROUND

In a substantial number of patients with non-cystic fibrosis (CF) bronchiectasis an etiology cannot be found. Various complex immunodeficiency syndromes account for a significant portion of these patients but the mechanism elucidating the predisposition for suppurative lung disease often remains unknown.

OBJECTIVE

To investigate the cause and mechanism predisposing a patient to severe bronchiectasis.

METHODS

A patient presenting with severe non-CF bronchiectasis was investigated. Whole exome analysis (WES) was performed and complemented by extensive immunophenotyping.

RESULTS

The genetic analysis revealed an autosomal dominant gain-of-function mutation (AD- GOF) in the signal transducer and activator of transcription 1 (STAT1) in the patient. STAT1 phosphorylation studies showed increased phosphorylation of STAT1 after stimulation with interferon γ (IFN-γ). Immunophenotyping showed normal counts of CD4 and CD8 T cells, B and NK cells, but a reduction of all memory B cells especially class switched memory B cells. Minor changes in the CD8 T cell subpopulations were seen.

CONCLUSIONS

Early use of WES in the investigation of non-CF bronchiectasis was highly advantageous. The degree of impairment in class-switched memory B cells may predispose patients with AD- GOF mutations in STAT1 to suppurative sinopulmonary disease.

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

BACKGROUND

Gain-of-function (GOF) mutations in the human signal transducer and activator of transcription 1 (STAT1) manifest in immunodeficiency and autoimmunity with impaired T_H17 cell 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.

OBJECTIVE

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.

METHODS

We used in vitro polarization assays, as well as phenotypic and functional analysis of STAT1-mutated patient cells.

RESULTS

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 T_H1 and follicular T helper cell and suppressed T_H17 cell 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 T_H1 and follicular T helper cell responses, improved T_H17 differentiation, cured mucocutaneous candidiasis, and maintained remission of immune-mediated cytopenias.

CONCLUSIONS

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.

Alanine-scanning mutagenesis of human signal transducer and activator of transcription 1 to estimate loss- or gain-of-function variants

BACKGROUND

Germline heterozygous mutations in human signal transducer and activator of transcription 1 (STAT1) can cause loss of function (LOF), as in patients with Mendelian susceptibility to mycobacterial diseases, or gain of function (GOF), as in patients with chronic mucocutaneous candidiasis. LOF and GOF mutations are equally rare and can affect the same domains of STAT1, especially the coiled-coil domain (CCD) and DNA-binding domain (DBD). Moreover, 6% of patients with chronic mucocutaneous candidiasis with a GOF STAT1 mutation have mycobacterial disease, obscuring the functional significance of the identified STAT1 mutations. Current computational approaches, such as combined annotation-dependent depletion, do not distinguish LOF and GOF variants.

OBJECTIVE

We estimated variations in the CCD/DBD of STAT1.

METHODS

We mutagenized 342 individual wild-type amino acids in the CCD/DBD (45.6% of full-length STAT1) to alanine and tested the mutants for STAT1 transcriptional activity.

RESULTS

Of these 342 mutants, 201 were neutral, 30 were LOF, and 111 were GOF mutations in a luciferase assay. This assay system correctly estimated all previously reported LOF mutations (100%) and slightly fewer GOF mutations (78.1%) in the CCD/DBD of STAT1. We found that GOF alanine mutants occurred at the interface of the antiparallel STAT1 dimer, suggesting that they destabilize this dimer. This assay also precisely predicted the effect of 2 hypomorphic and dominant negative mutations, E157K and G250E, in the CCD of STAT1 that we found in 2 unrelated patients with Mendelian susceptibility to mycobacterial diseases.

CONCLUSION

The systematic alanine-scanning assay is a useful tool to estimate the GOF or LOF status and the effect of heterozygous missense mutations in STAT1 identified in patients with severe infectious diseases, including mycobacterial and fungal diseases.

Genetic, immunological, and clinical features of patients with bacterial and fungal infections due to inherited IL-17RA deficiency

Chronic mucocutaneous candidiasis (CMC) is defined as recurrent or persistent infection of the skin, nails, and/or mucosae with commensal Candida species. The first genetic etiology of isolated CMC-autosomal recessive (AR) IL-17 receptor A (IL-17RA) deficiency-was reported in 2011, in a single patient. We report here 21 patients with complete AR IL-17RA deficiency, including this first patient. Each patient is homozygous for 1 of 12 different IL-17RA alleles, 8 of which create a premature stop codon upstream from the transmembrane domain and have been predicted and/or shown to prevent expression of the receptor on the surface of circulating leukocytes and dermal fibroblasts. Three other mutant alleles create a premature stop codon downstream from the transmembrane domain, one of which encodes a surface-expressed receptor. Finally, the only known missense allele (p.D387N) also encodes a surface-expressed receptor. All of the alleles tested abolish cellular responses to IL-17A and -17F homodimers and heterodimers in fibroblasts and to IL-17E/IL-25 in leukocytes. The patients are currently aged from 2 to 35 y and originate from 12 unrelated kindreds. All had their first CMC episode by 6 mo of age. Fourteen patients presented various forms of staphylococcal skin disease. Eight were also prone to various bacterial infections of the respiratory tract. Human IL-17RA is, thus, essential for mucocutaneous immunity to Candida and Staphylococcus, but otherwise largely redundant. A diagnosis of AR IL-17RA deficiency should be considered in children or adults with CMC, cutaneous staphylococcal disease, or both, even if IL-17RA is detected on the cell surface.

Chronic mucocutaneous candidiasis disease associated with inborn errors of IL-17 immunity

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent infections affecting the nails, skin and oral and genital mucosae caused by Candida spp., mainly Candida albicans. CMC is an infectious phenotype in patients with inherited or acquired T-cell deficiency. Patients with autosomal-dominant (AD) hyper IgE syndrome (HIES), AD signal transducer and activator of transcription 1 (STAT1) gain-of-function, autosomal-recessive (AR) deficiencies in interleukin (IL)-12 receptor β1 (IL-12Rβ1), IL-12p40, caspase recruitment domain-containing protein 9 (CARD9) or retinoic acid-related orphan receptor γT (RORγT) or AR autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) develop CMC as a major infectious phenotype that is categorized as Syndromic CMC. In contrast, CMC disease (CMCD) is typically defined as CMC in patients in the absence of any other prominent clinical signs. This definition is not strict; thus, CMCD is currently used to refer to patients presenting with CMC as the main clinical phenotype. The etiology of CMCD is not related to genes that cause severe combined immunodeficiency or combined immunodeficiency, nor to genes responsible for Syndromic CMC. Four genetic etiologies, AR IL-17 receptor A, IL-17 receptor C and ACT1 deficiencies, and AD IL-17F deficiency, are reported to underlie CMCD. Each of these gene defects directly has an impact on IL-17 signaling, suggesting their nonredundant role in host mucosal immunity to Candida. Here, we review current knowledge focusing on IL-17 signaling and the genetic etiologies responsible for, and associated with, CMC.

A heterozygous dominant-negative mutation in the coiled-coil domain of STAT1 is the cause of autosomal-dominant Mendelian susceptibility to mycobacterial diseases

Heterozygous dominant-negative mutations of STAT1 are responsible for autosomal-dominant Mendelian susceptibility to mycobacterial diseases (AD-MSMD). So far, only 7 mutations have been previously described and are localized to 3 domains: the DNA-binding domain, the SH₂ domain, and the tail segment. In this study, we demonstrated the first coiled-coil domain (CCD) mutation of c.749G>C, p.G250A (G250A) in STAT1 as a genetic cause of AD-MSMD in a patient with mycobacterial multiple osteomyelitis. This de novo heterozygous mutation was shown to have a dominant-negative effect on the gamma-activated sequence (GAS) transcriptional activity following IFN-γ stimulation, which could be attributable to the abolished phosphorylation of STAT1 from the wild-type (WT) allele. The three-dimensional structure of STAT1 revealed the G250 residue was located distant from a cluster of residues affected by gain-of-function mutations responsible for chronic mucocutaneous candidiasis.

Basic Genetics and Immunology of Candida Infections

Candida infections can cause superficial and invasive disease. Several essential mechanisms underlying the pathogenesis of these infections were known for some time, such as neutropenia predisposing to invasive disease, and CD4 lymphopenia causing increased susceptibility to mucosal candidiasis. However, the development of novel genetic screening techniques has led to several new insights in the genetics and immunology of candida infections. This article highlights novel insights in the pathogenesis of mucocutaneous and invasive candidiasis that have been identified in recent years.

Heterozygous STAT1 gain-of-function mutations underlie an unexpectedly broad clinical phenotype

Since their discovery in patients with autosomal dominant (AD) chronic mucocutaneous candidiasis (CMC) in 2011, heterozygous STAT1 gain-of-function (GOF) mutations have increasingly been identified worldwide. The clinical spectrum associated with them needed to be delineated. We enrolled 274 patients from 167 kindreds originating from 40 countries from 5 continents. Demographic data, clinical features, immunological parameters, treatment, and outcome were recorded. The median age of the 274 patients was 22 years (range, 1-71 years); 98% of them had CMC, with a median age at onset of 1 year (range, 0-24 years). Patients often displayed bacterial (74%) infections, mostly because of Staphylococcus aureus (36%), including the respiratory tract and the skin in 47% and 28% of patients, respectively, and viral (38%) infections, mostly because of Herpesviridae (83%) and affecting the skin in 32% of patients. Invasive fungal infections (10%), mostly caused by Candida spp. (29%), and mycobacterial disease (6%) caused by Mycobacterium tuberculosis, environmental mycobacteria, or Bacille Calmette-Guérin vaccines were less common. Many patients had autoimmune manifestations (37%), including hypothyroidism (22%), type 1 diabetes (4%), blood cytopenia (4%), and systemic lupus erythematosus (2%). Invasive infections (25%), cerebral aneurysms (6%), and cancers (6%) were the strongest predictors of poor outcome. CMC persisted in 39% of the 202 patients receiving prolonged antifungal treatment. Circulating interleukin-17A-producing T-cell count was low for most (82%) but not all of the patients tested. STAT1 GOF mutations underlie AD CMC, as well as an unexpectedly wide range of other clinical features, including not only a variety of infectious and autoimmune diseases, but also cerebral aneurysms and carcinomas that confer a poor prognosis.

The Evolving View of IL-17-Mediated Immunity in Defense Against Mucocutaneous Candidiasis in Humans

The discovery of interleukin (IL)-17-mediated immunity has provided a robust framework upon which our current understanding of the mechanism involved in host defense against mucocutaneous candidiasis (CMC) has been built. Studies have shed light on how pattern recognition receptors expressed by innate immune cells recognize various components of Candida cell wall. Inborn errors of immunity affecting IL-17+ T cell differentiation have recently been defined, such as deficiencies of signal transducer and activator of transcription (STAT)3, STAT1, IL-12Rβ1 and IL-12p40, and caspase recruitment domain 9. Impaired receptor-ligand coupling was identified in patients with IL-17F and IL-17 receptor A (IL17RA) deficiency and autoimmune polyendocrine syndrome (APS) type 1. Mutation in the nuclear factor kappa B activator (ACT) 1 was described as a cause of impaired IL-17R-mediated signaling. CMC may be part of a complex clinical phenotype like in patients with deficiencies of STAT3, IL-12Rβ1/IL-12p40 and APS-1 or may be the only or dominant phenotypic manifestation of disease which is referred to as CMC disease. CMCD may result from deficiencies of STAT1, IL-17F, IL-17RA and ACT1. In this review we discuss how recent research on IL-17-mediated immunity shed light on host defense against mucocutaneous infection by Candida and how the discovery of various germ-line mutations and the characterization of associated clinical phenotypes have provided insights into the role of CD4+IL-17+ lymphocytes in the regulation of anticandidal defense of body surfaces.

Heterozygous STAT1 gain-of-function mutations underlie an unexpectedly broad clinical phenotype

Since their discovery in patients with autosomal dominant (AD) chronic mucocutaneous candidiasis (CMC) in 2011, heterozygous STAT1 gain-of-function (GOF) mutations have increasingly been identified worldwide. The clinical spectrum associated with them needed to be delineated. We enrolled 274 patients from 167 kindreds originating from 40 countries from 5 continents. Demographic data, clinical features, immunological parameters, treatment, and outcome were recorded. The median age of the 274 patients was 22 years (range, 1-71 years); 98% of them had CMC, with a median age at onset of 1 year (range, 0-24 years). Patients often displayed bacterial (74%) infections, mostly because of Staphylococcus aureus (36%), including the respiratory tract and the skin in 47% and 28% of patients, respectively, and viral (38%) infections, mostly because of Herpesviridae (83%) and affecting the skin in 32% of patients. Invasive fungal infections (10%), mostly caused by Candida spp. (29%), and mycobacterial disease (6%) caused by Mycobacterium tuberculosis, environmental mycobacteria, or Bacille Calmette-Guérin vaccines were less common. Many patients had autoimmune manifestations (37%), including hypothyroidism (22%), type 1 diabetes (4%), blood cytopenia (4%), and systemic lupus erythematosus (2%). Invasive infections (25%), cerebral aneurysms (6%), and cancers (6%) were the strongest predictors of poor outcome. CMC persisted in 39% of the 202 patients receiving prolonged antifungal treatment. Circulating interleukin-17A-producing T-cell count was low for most (82%) but not all of the patients tested. STAT1 GOF mutations underlie AD CMC, as well as an unexpectedly wide range of other clinical features, including not only a variety of infectious and autoimmune diseases, but also cerebral aneurysms and carcinomas that confer a poor prognosis.

A novel gain-of-function STAT1 mutation resulting in basal phosphorylation of STAT1 and increased distal IFN-γ-mediated responses in chronic mucocutaneous candidiasis

Gain-of-function STAT1 mutations have recently been associated with autosomal dominant chronic mucocutaneous candidiasis (CMC). The purpose of this study was to characterize the three members of a non-consanguineous family, the father and his two sons, who presented with recurrent oral thrush and ocular candidiasis since early childhood. The three patients had reduced levels of IL-17-producing T cells. This reduction affected specifically IL-17(+)IFN-γ(-) T cells, because the levels of IL-17(+)IFN-γ(+) T cells were similar to controls. We found that PBMC (peripheral blood mononuclear cells) from the patients did not respond to Candida albicans ex vivo. Moreover, after polyclonal activation, patients' PBMC produced lower levels of IL-17 and IL-6 and higher levels of IL-4 than healthy controls. Genetic analyses showed that the three patients were heterozygous for a new mutation in STAT1 (c.894A>C, p.K298N) that affects a highly conserved residue of the coiled-coil domain of STAT1. STAT1 phosphorylation levels were significantly higher in patients' cells than in healthy controls, both in basal conditions and after IFN-γ stimulation, suggesting a permanent activation of STAT1. Cells from the patients also presented increased IFN-γ-mediated responses measured as MIG and IP-10 production. In conclusion, we report a novel gain-of-function mutation in the coiled-coil domain of STAT1, which increases STAT1 phosphorylation and impairs IL-17-mediated immunity. The mutation is responsible for CMC in this family with autosomal dominant inheritance of the disease.

Progressive Multifocal Leukoencephalopathy in Primary Immune Deficiencies: Stat1 Gain of Function and Review of the Literature

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) is a rare, severe, otherwise fatal viral infection of the white matter of the brain caused by the polyomavirus JC virus, which typically occurs only in immunocompromised patients. One patient with dominant gain-of-function (GOF) mutation in signal transducer and activator of transcription 1 (STAT1) with chronic mucocutaneous candidiasis and PML was reported previously. We aim to identify the molecular defect in 3 patients with PML and to review the literature on PML in primary immune defects (PIDs).

METHODS

STAT1 was sequenced in 3 patients with PML. U3C cell lines were transfected with STAT1 and assays to search for STAT1 phosphorylation, transcriptional response, and target gene expression were performed.

RESULTS

We identified 3 new unrelated cases of PML in patients with GOF STAT1 mutations, including the novel STAT1 mutation, L400Q. These STAT1 mutations caused delayed STAT1 dephosphorylation and enhanced interferon-gamma-driven responses. In our review of the literature regarding PML in primary immune deficiencies we found 26 cases, only 54% of which were molecularly characterized, the remainder being syndromically diagnosed only.

CONCLUSIONS

The occurrence of PML in 4 cases of STAT1 GOF suggests that STAT1 plays a critical role in the control of JC virus in the central nervous system.

Common variable immunodeficiency, impaired neurological development and reduced numbers of T regulatory cells in a 10-year-old boy with a STAT1 gain-of-function mutation

Recently, gain-of-function (GOF) mutations in the gene encoding signal transducer and activator of transcription 1 (STAT1) have been associated with chronic mucocutaneous candidiasis (CMC). This case report describes a 10-year-old boy presenting with signs of common variable immunodeficiency (CVID), failure to thrive, impaired neurological development, and a history of recurrent mucocutaneous Candida infections. Sequencing of the STAT1 gene identified a heterozygous missense mutation in exon 7 encoding the STAT1 coiled-coil domain (c.514T>C, p.Phe172Leu). In addition to hypogammaglobulinemia with B-cell deficiency, and a low percentage of Th17 cells, immunological analysis of the patient revealed a marked depletion of forkhead-box P3(+)-expressing regulatory T cells (Tregs). In vitro stimulation of T cells from the patient with interferon-α (IFNα) and/or IFNɣ resulted in a significantly increased expression of STAT1-regulated target genes such as MIG1, IRF1, MX1, MCP1/CCL2, IFI-56K, and CXCL10 as compared to IFN-treated cells from a healthy control, while no IFNα/ɣ-mediated up-regulation of the FOXP3 gene was found. These data demonstrate that the STAT1 GOF mutation F172L, which results in impaired stability of the antiparallel STAT1 dimer conformation, is associated with inhibited Treg cell development and neurological symptoms.

Autosomal dominant transmission of signal transduction and activator of transcription 1 (STAT1) mutation (Thr385Met) and extended lifespan

Introduction: Heterozygous mutations in signal transducer and activator of transcription 1 (STAT1) have been associated with selective deficiencies to mycobacterial or fungal infections. Recent reports revealed that patients found to carry de novo heterozygous mutations in STAT1 encoding specific amino acid substitutions can go on to develop progressive combined immunodeficiency, distinct from the limited susceptibilities to infection previously reported for heterozygous STAT1 mutations.

Objectives: We present a case of a mother and her son with chronic mucocutaneous candidiasis and T-cell dysfunction, both of whom lived longer than projected life expectancy with a heterozygous STAT1 mutation. The son lived to the age of 20 years and the mother to the age of 32 years.

Methods: The son's blood sequencing of STAT1 was performed on a pure T-cell lineage at The Hospital for Sick Children and the Canadian Center for Primary Immunodeficiency, Toronto, Ontario.

Results: STAT1 analysis revealed a heterozygous DNA binding domain mutation at Thr385Met. The patient proceeded to develop fulminant progressive multifocal leukoencephalopathy that ultimately led to his death. The patient's mother, although never confirmed to have STAT1 mutation with formal blood sequencing, had multiple comorbidities including progressive lymphopenia, hypogammaglobulinemia, recurrent Pseudomonas pneumonias with associated bronchiectasis, end-stage kidney disease requiring hemodialysis, and ultimately death due to multiple end organ failure associated sepsis.

Conclusion: This is the first autosomal dominant transmission of the STAT1 DNA binding domain Thr385Met mutation with an extended lifespan.

Statement of Novelty: Previous patients found to have heterozygous mutations of STAT1 that were associated with progressive combined immunodeficiency, arose de novo in each case. Presumed autosomal dominant transmission of a heterozygous STAT1 DNA binding domain Thr385Met mutation has not been reported.

The effects of STAT1 dysfunction on the gut

Introduction: Mutations in the signal transducer and activator of transcription1 (STAT1) have been associated with a variety of clinical patterns. Interestingly patients with heterozygous mutations in the DNA binding domain (DBD) of STAT1 suffer acute and chronic colitis.

Methods: To further analyze the role of STAT1 deficiency in intestinal inflammation, we employed protein expression analysis of total and activated STAT1 in intestinal biopsy samples from 2 patients with heterozygous mutations in the DBD of the STAT1 gene.

Results: Both patients showed clinical and histological features of colitis. Total and activated STAT1 were decreased in duodenal and colonic enterocytes, and total STAT1 was found to be mislocalized in aggregates subapically. In addition, intestinal biopsy samples showed decreased numbers of lymphocytes. Patient-derived lymphoblasts demonstrated lack of viability and high susceptibility for cell death.

Conclusion: STAT1 expression and distribution in the gut of patients with mutations in the DBD are abnormal, suggesting a primary role of STAT1 dysfunction in enterocytes in addition to the secondary effect of aberrant inflammation.

Statement of novelty: Colitis associated with STAT1 mutations appears to have unique features distinct from typical inflammatory bowel disease.