A 1-Year-Old Girl with a Gain-of-Function STAT1 Mutation Treated with Hematopoietic Stem Cell Transplantation

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.

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.

Single-cell RNA sequencing combined with whole exome sequencing reveals the landscape of the immune pathogenic response to chronic mucocutaneous candidiasis with STAT1 GOF mutation

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent infections with Candida of the skin, nails, and mucous membranes (e.g., mouth, esophagus, and vagina). Compared with that of other infectious diseases, the immune pathogenic mechanism of CMC is still poorly understood. We identified a signal transducer and activator of transcription 1 gain-of-function (c.Y289C) mutation in a CMC patient. Single-cell transcriptional profiling on peripheral blood mononuclear cells from this patient revealed decreases in immature B cells and monocytes. Further analysis revealed several differentially expressed genes related to immune regulation, including RGS1, TNFAIP3, S100A8/A9, and CTSS. In our review of the literature on signal transducer and activator of transcription 1 gain-of-function (c.Y289C) mutations, we identified seven cases in total. The median age of onset for CMC (n=4, data lacking for three cases) was 10.5 years (range: birth to 11 years), with an average onset age of 8 years. There were no reports linking tumors to the c.Y289C mutation, and the incidence of pre-existing clinical disease in patients with the c.Y289C mutation was similar to previous data.

Main human inborn errors of immunity leading to fungal infections

BACKGROUND

The host molecular and genetic features are essential in providing susceptibility to a broad spectrum of fungal infections; most of these do not cause disease in healthy individuals because of mutual benefits with opportunistic fungi besides the host's capacity to control the infections. In contrast, patients with primary immunodeficiency (PID) can develop mild superficial to life-threatening invasive infections. In the last years, thanks to next-generation sequencing (NGS), several inborn-error variants have been discovered in genes encoding protein acting against fungal infections, contributing to better defining the role of innate and adaptive immunity cooperation during infection resolution. Candida fungal infection, that sometimes-striking healthy subjects, is responsible for the chronic mucocutaneous candidiasis (CMC) that is one of the principal clinical manifestations occurring in several rare PIDs associated with an inborn error of IL17-immunity.

OBJECTIVE

This review aimed to provide an overview of CMC-derived genetic defects, including IL17-deficiencies (IL17A, IL17F, IL17RA, IL17RC), STAT1 gain-of-function (GOF)- deficiency, STAT3-HIES and CARD9-deficiency.

SOURCES

We carried out detailed research work to identify interesting articles, commentaries, and reviews in the PubMed literature to ensure a correct and updated for this narrative review.

CONTENT

We propose an in-depth description and an update of genetic and cellular mechanisms underlying fungal infections, focusing on the IL17-mediated response, a report of clinical manifestations and describe therapeutic options.

IMPLICATION

This narrative review will help clinician to identify the correct management of patients based on molecular and cellular findings underlying pathogenic mechanisms of different IEIs. Moreover achieve the genetic diagnosis will be useful to offer genetic counselling intra- and inter-family and to ensure a personalized treatment of patients.

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.

Autosomal dominant chronic mucocutaneous candidiasis with STAT1 mutation can be associated with chronic active hepatitis: A case report

BACKGROUND

Chronic mucocutaneous candidiasis (CMC) is a heterogeneous primary immunodeficiency disease characterized by chronic or recurrent Candida infections of the skin, nails, and mucosa and is mostly associated with STAT1 gain-of-function (GOF) mutation (GOF-STAT1 mutation).

CASE PRESENTATION

A two-year-old girl was presented with recurrent liver dysfunction, oral candidiasis, acute bronchial pneumonia, and cytomegalovirus infection. Even after a series of treatments, including antifungal voriconazole, nystatin treatment for oral Candida, antibiotics against bacterial infection, and bicyclol to protect the liver, the child still exhibited signs of splenomegaly. Although we performed relevant etiological tests on the child and conducted histopathology and electron microscopic examination of the liver, we could not explain the clinical symptoms. So, a genetic test was conducted to clarify the diagnosis. Since the child suffered recurrent fungal infections, we speculated that she had combined immunodeficiency. Therefore we performed high-precision clinical display PLUS detection and found that the transcription factor STAT1 had a heterozygous GOF mutation (p. R274W) in its coiled-coil domain.

CONCLUSION

The clinical manifestations of chronic mucocutaneous candidiasis caused by GOF-STAT1 mutations are complex and range from mild local fungal infections to severe systemic diseases and are sometimes fatal. Clinicians need to be aware of the possibility of this disease in children with recurrent fungal infections for early diagnosis and treatment.

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.

The Skin as a Window into Primary Immune Deficiency Diseases: Atopic Dermatitis and Chronic Mucocutaneous Candidiasis

Primary immune deficiency diseases characteristically present with recurrent, severe, or unusual infections. These infections may often involve the skin, with mucocutaneous candidal infections seen in a variety of different primary immune deficiencies. Primary immune deficiencies may also present with noninfectious cutaneous complications, of which eczema is the most common. In a patient with suspected primary immune deficiency, the presence of eczema or candidal skin infections offers critical information about the underlying immune defect, either the presence of atopy or defect in the T_H17 pathway, respectively. These skin manifestations also are often early or heralding findings of the underlying immunologic disease. Therefore, awareness of associations between these skin findings and specific immune deficiencies may aide in the early detection and treatment of serious or life-threatening immunologic defects. This review specifically will focus on the primary immune deficiencies commonly associated with eczema or mucocutaneous candidiasis.

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.

Ruxolitinib treatment of a patient with steroid-dependent severe autoimmunity due to STAT1 gain-of-function mutation

Signal transducer and activator of transcription 1 gain-of-function (STAT1 GOF) mutations are the most common cause of chronic mucocutaneous candidiasis (CMC). We report the effect of oral ruxolitinib, an inhibitor of Janus kinase (JAK) family tyrosine kinases, on the clinical and immune status of a 3-year-old male with steroid-dependent severe autoimmunity due to a STAT1 GOF T385M mutation. The patient's susceptibility to infection improved with antimicrobial prophylaxis and immunoglobulin replacement therapy, but he continued to exhibit severely disabling symptoms of autoimmunity. More than one-third of patients with STAT1 GOF mutations present with autoimmune manifestations, and this patient's mutation was reported to cause CMC with autoimmunity. We analyzed the interleukin (IL)-17A and IFN-γ levels and immunophenotype by flow cytometry before and during treatment with ruxolitinib. The peripheral IL-17A level did not increase, but the IFN-γ level decreased after 4 months of therapy. The STAT1 phosphorylation level decreased significantly upon stimulation of patient cells with IFN-γ. Clinically, cytomegalovirus reactivation occurred, but was controlled. No other adverse effect was noted. We report the potential of JAK1/2 inhibition with ruxolitinib for both CMC and steroid-dependent autoimmunity. However, long-term administration is necessary, as the effect is not sustained after treatment is discontinued.

Targeted Therapy with Biologicals and Small Molecules in Primary Immunodeficiencies

Primary immunodeficiencies are disorders resulting from mutations in genes involved in immune defense and immune regulation. These conditions are characterized by various combinations of recurrent infections, autoimmunity, lymphoproliferation, inflammatory manifestations, and malignancy. In the last 20 years, newborn screening programs and next generation sequencing techniques have increased the ability to diagnose primary immunodeficiencies. Furthermore, an advanced understanding of the molecular basis of these inherited disorders has led to the implementation of targeted therapies that utilize small molecules and biologics to modulate the activity of impaired intracellular pathways. This article will discuss selected primary immunodeficiencies, the genetic defects of which have been recently studied and are amenable to targeted therapy as a reflection of the potential of precision medicine in the future.

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.

Inborn Errors of Immunity With Immune Dysregulation: From Bench to Bedside

Inborn errors of immunity are genetic disorders with broad clinical manifestations, ranging from increased susceptibility to infections to significant immune dysregulation, often leading to multiple autoimmune phenomena, lymphoproliferation, and malignancy. The treatment is challenging as it requires careful balancing of immunosuppression in subjects at increased risk of infections. Recently, the improved ability to define inborn errors of immunity pathophysiology at the molecular level has set the basis for the development of targeted therapeutic interventions. Such a "precision medicine" approach is mainly bases on the use of available small molecules and biologics to target a specific cell function. In this article, we summarize the clinical and laboratory features of various recently described inborn errors of immunity associated with immune dysregulation and hyperinflammation in which mechanism-based therapeutic approaches have been implemented.

Hematopoietic Stem Cell Transplantation in Patients with Heterozygous STAT1 Gain-of-Function Mutation

PURPOSE

Human signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations present with a broad range of manifestations ranging from chronic mucocutaneous candidiasis and autoimmunity to combined immunodeficiency (CID). So far, there is very limited experience with hematopoietic stem cell transplantation (HSCT) as a therapeutic modality in this disorder. Here, we describe two patients with heterozygous STAT1 GOF mutations mimicking CID who were treated with HSCT.

METHODS

Data on the HSC sources, conditioning regimen, graft-versus-host disease (GvHD) and antimicrobial prophylaxis, and the post-transplant course including engraftment, GvHD, transplant-related complications, infections, chimerism, and survival were evaluated. Pre- and post-transplant immunological studies included enumeration of circulating interferon gamma (IFN-γ)- and interleukin 17 (IL-17)-expressing CD4⁺ T cells and analysis of IFN-β-induced STAT1 phosphorylation in patient 1 (P1)'s T cells.

RESULTS

P1 was transplanted with cord blood from an HLA-identical sibling, and P2 with bone marrow from a fully matched unrelated donor using a reduced toxicity conditioning regimen. While P1 completely recovered from her disease, P2 suffered from systemic CMV disease and secondary graft failure and died due to severe pulmonary involvement and hemorrhage. The dysregulated IFN-γ production, suppressed IL-17 response, and enhanced STAT1 phosphorylation previously found in the CD4⁺ T cells of P1 were normalized following transplantation.

CONCLUSION

HSCT could be an alternative and curative therapeutic option for selected STAT1 GOF mutant patients with progressive life-threatening disease unresponsive to conventional therapy. Morbidity and mortality-causing complications included secondary graft failure, infections, and bleeding.

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.

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.

Targeted strategies directed at the molecular defect: Toward precision medicine for select primary immunodeficiency disorders

Primary immunodeficiency disorders (PIDs) represent a range of genetically determined diseases that typically have increased susceptibility to infections and in many cases also have evidence of immune dysregulation that often presents as autoimmunity. Most recently, the concept of gain-of-function mutations associated with PIDs has become well recognized and adds a new dimension to the understanding of this group of disorders, moving beyond the more commonly seen loss-of-function mutations. The rapidly expanding genetic defects that have been identified in patients with previously uncharacterized PIDs has opened up the potential for targeted therapy directed at the specific disease-causing abnormality. This has been driven by linking PID-specific genetic defects to the associated unique abnormalities in cellular signaling pathways amenable to directed therapies. These include agents that either block overactive or enhance underresponsive cellular pathways. Selected primary immunodeficiencies were chosen, the genetic defects of which have been recently characterized and are amenable to targeted therapy, as a reflection of the power of precision medicine.

Hematopoietic stem cell transplantation in patients with gain-of-function signal transducer and activator of transcription 1 mutations

BACKGROUND

Gain-of-function (GOF) mutations in signal transducer and activator of transcription 1 (STAT1) cause susceptibility to a range of infections, autoimmunity, immune dysregulation, and combined immunodeficiency. Disease manifestations can be mild or severe and life-threatening. Hematopoietic stem cell transplantation (HSCT) has been used in some patients with more severe symptoms to treat and cure the disorder. However, the outcome of HSCT for this disorder is not well established.

OBJECTIVE

We sought to aggregate the worldwide experience of HSCT in patients with GOF-STAT1 mutations and to assess outcomes, including donor engraftment, overall survival, graft-versus-host disease, and transplant-related complications.

METHODS

Data were collected from an international cohort of 15 patients with GOF-STAT1 mutations who had undergone HSCT using a variety of conditioning regimens and donor sources. Retrospective data collection allowed the outcome of transplantation to be assessed. In vitro functional testing was performed to confirm that each of the identified STAT1 variants was in fact a GOF mutation.

RESULTS

Primary donor engraftment in this cohort of 15 patients with GOF-STAT1 mutations was 74%, and overall survival was only 40%. Secondary graft failure was common (50%), and posttransplantation event-free survival was poor (10% by 100 days). A subset of patients had hemophagocytic lymphohistiocytosis before transplant, contributing to their poor outcomes.

CONCLUSION

Our data indicate that HSCT for patients with GOF-STAT1 mutations is curative but has significant risk of secondary graft failure and death.

Nonclassic Inflammatory Bowel Disease in Young Infants: Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-Linked Syndrome, and Other Disorders

This article discusses non-classical forms of inflammatory bowel disease (IBD) mainly occurs in infants and very young children. Defects in every aspect of the immune system, such as neutrophils, T-cell and B-cell lymphocytes, and macrophages are associated with IBD in infants. Also, non lympho-hematopoietic defects with primary defects in enterocytes can also lead to IBD-like manifestations. Clinical vignettes are presented and the genetic origins and possible management strategies are outlined. Early evaluation of these patients is important because identification of underlying immune defects would facilitate the use of better-targeted therapy for the specific genetic defect.

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.

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.

Severe Early-Onset Combined Immunodeficiency due to Heterozygous Gain-of-Function Mutations in STAT1

PURPOSE

Loss and gain-of-function (GOF) mutations in human signal transducer and activator of transcription 1 (STAT1) lead to distinct phenotypes. Although recurrent infections are common to both types of STAT1 mutations, GOF mutations are distinguished by chronic mucocutaneous candidiasis and autoimmunity. However, the clinical spectra of STAT1 GOF mutations continue to expand. We here describe two patients with STAT1 GOF mutations presenting early in life with combined immunodeficiency (CID).

METHODS

Clinical data and laboratory findings including immunophenotyping, level of interferon (IFN)-γ/IL-17(+) T cells, interferon-induced STAT1 phosphorylation, and JAK inhibitor assays were evaluated. Sequencing of STAT1 gene was performed by Sanger sequencer.

RESULTS

Patient 1 (P1) had persistent oral candidiasis and cytomegalovirus (CMV) infection since 2 months of age and later developed cavitary lung lesions due to Mycobacterium tuberculosis. Patient 2 (P2) presented with oral candidiasis and recurrent pneumonia at 4 months of age and subsequently developed CMV pneumonitis. Both patients suffered heterozygous missense mutations in STAT1, leading to deleterious amino acid substitutions in the DNA binding domain (P1: c.1154C > T; p.T385M; P2. c.971G > T; p.C324F). Circulating CD4(+) T cells of both patients exhibited increased interferon-γ and decreased IL-17 expression as compared to controls. They also exhibited increased IFN-β and -γ-induced STAT1 phosphorylation that was reversed upon treatment with the JAK kinase inhibitor ruxolitinib.

CONCLUSION

STAT1 GOF mutations may present early in life with CID, consistent with the clinical heterogeneity of the disease. JAK kinase inhibitors may potentially be useful in some patients as adjunct therapy pending definitive treatment with bone marrow transplantation.

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.

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.

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.

The Extended Clinical Phenotype of 26 Patients with Chronic Mucocutaneous Candidiasis due to Gain-of-Function Mutations in STAT1

Purpose

Gain-of-function (GOF) mutations in the signal transducer and activator of transcription 1 (STAT1) result in unbalanced STAT signaling and cause immune dysregulation and immunodeficiency. The latter is often characterized by the susceptibility to recurrent Candida infections, resulting in the clinical picture of chronic mucocutaneous candidiasis (CMC). This study aims to assess the frequency of GOF STAT1 mutations in a large international cohort of CMC patients.

Methods

STAT1 was sequenced in genomic DNA from 57 CMC patients and 35 healthy family members. The functional relevance of nine different STAT1 variants was shown by flow cytometric analysis of STAT1 phosphorylation in patients’ peripheral blood cells (PBMC) after stimulation with interferon (IFN)-α, IFN-γ or interleukin-27 respectively. Extended clinical data sets were collected and summarized for 26 patients.

Results

Heterozygous mutations within STAT1 were identified in 35 of 57 CMC patients (61 %). Out of 39 familial cases from 11 families, 26 patients (67 %) from 9 families and out of 18 sporadic cases, 9 patients (50 %) were shown to have heterozygous mutations within STAT1. Thirteen distinct STAT1 mutations are reported in this paper. Eight of these mutations are known to cause CMC (p.M202V, p.A267V, p.R274W, p.R274Q, p.T385M, p.K388E, p.N397D, and p.F404Y). However, five STAT1 variants (p.F172L, p.Y287D, p.P293S, p.T385K and p.S466R) have not been reported before in CMC patients.

Conclusion

STAT1 mutations are frequently observed in patients suffering from CMC. Thus, sequence analysis of STAT1 in CMC patients is advised. Measurement of IFN- or IL-induced STAT1 phosphorylation in PBMC provides a fast and reliable diagnostic tool and should be carried out in addition to genetic testing.

Inherited IL-17RC deficiency in patients with chronic mucocutaneous candidiasis

Autosomal-recessive IL-17RA, IL-17RC, and ACT1 deficiencies and autosomal-dominant IL-17F deficiency in humans underlie susceptibility to chronic mucocutaneous candidiasis.

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent infections of the skin, nail, oral, and genital mucosae with Candida species, mainly C. albicans. Autosomal-recessive (AR) IL-17RA and ACT1 deficiencies and autosomal-dominant IL-17F deficiency, each reported in a single kindred, underlie CMC in otherwise healthy patients. We report three patients from unrelated kindreds, aged 8, 12, and 37 yr with isolated CMC, who display AR IL-17RC deficiency. The patients are homozygous for different nonsense alleles that prevent the expression of IL-17RC on the cell surface. The defect is complete, abolishing cellular responses to IL-17A and IL-17F homo- and heterodimers. However, in contrast to what is observed for the IL-17RA– and ACT1-deficient patients tested, the response to IL-17E (IL-25) is maintained in these IL-17RC–deficient patients. These experiments of nature indicate that human IL-17RC is essential for mucocutaneous immunity to C. albicans but is otherwise largely redundant.

Immunological loss-of-function due to genetic gain-of-function in humans: autosomal dominance of the third kind

All the human primary immunodeficiencies (PIDs) recognized as such in the 1950s were Mendelian traits and, whether autosomal or X-linked, displayed recessive inheritance. The first autosomal dominant (AD) PID, hereditary angioedema, was recognized in 1963. However, since the first identification of autosomal recessive (AR), X-linked recessive (XR) and AD PID-causing genes in 1985 (ADA; severe combined immunodeficiency), 1986 (CYBB, chronic granulomatous disease) and 1989 (SERPING1; hereditary angioedema), respectively, the number of genetically defined AD PIDs has increased more rapidly than that of any other type of PID. AD PIDs now account for 61 of the 260 known conditions (23%). All known AR PIDs are caused by alleles with some loss-of-function (LOF). A single XR PID is caused by gain-of-function (GOF) mutations (WASP-related neutropenia, 2001). In contrast, only 44 of 61 AD defects are caused by LOF alleles, which exert dominance by haploinsufficiency or negative dominance. Since 2003, up to 17 AD disorders of the third kind, due to GOF alleles, have been described. Remarkably, six of the 17 genes concerned also harbor monoallelic (STAT3), biallelic (C3, CFB, CARD11, PIK3R1) or both monoallelic and biallelic (STAT1) LOF alleles in patients with other clinical phenotypes. Most heterozygous GOF alleles result in auto-inflammation, auto-immunity, or both, with a wide range of immunological and clinical forms. Some also underlie infections and, fewer, allergies, by impairing or enhancing immunity to non-self. Malignancies are also rare. The enormous diversity of immunological and clinical phenotypes is thought provoking and mirrors the diversity and pleiotropy of the underlying genotypes. These experiments of nature provide a unique insight into the quantitative regulation of human immunity.

A mutation in the STAT1 DNA-binding domain associated with hemophagocytic lymphohistocytosis

Introduction: The transcription factor Signal Transducer and Activator of Transcription 1 (STAT1) is a key element in many of the signalling cascades involved in immune system function. Different mutations in STAT1 are associated with heterogeneous clinical phenotypes that range from early fatality due to overwhelming infection to limited involvement of the mucus membrane with recurrent Candida infections. Multiple genes related to immune function have been associated with the development of hemophagocytic lymphohistiocytosis (HLH), but the association between STAT1 mutation and HLH has not been described in detail.

Methods: We report the genetic background of a patient with chronic mucocutaneous candidiasis (CMC) as well as an unusual clinical course.

Results: In this study we describe a patient with a mutation in the STAT1 DNA-binding domain and a history of CMC who developed a refractory and fatal case of HLH despite having bone marrow transplantation.

Conclusion: We describe a patient with refractory and fatal HLH who was found to have a mutation in the DNA-binding domain of STAT1.

Statement of novelty: The association of chronic mucocutaneous candidiasis with HLH.

Two novel gain-of-function mutations of STAT1 responsible for chronic mucocutaneous candidiasis disease: impaired production of IL-17A and IL-22, and the presence of anti-IL-17F autoantibody

Heterozygous gain-of-function (GOF) mutations of STAT1 are responsible for chronic mucocutaneous candidiasis disease (CMCD), one of the primary immunodeficiency diseases characterized by susceptibility to mucocutaneous Candida infection. To date, 30 aa changes have been reported: 21 in the coiled-coil domain and 9 in the DNA-binding domain. In this study, we report two novel STAT1 GOF mutations of p.K278E in coiled-coil domain and p.G384D in DNA-binding domain in Japanese CMCD patients. Ectopic expression of these STAT1 mutants in HeLa cells was associated with increased phosphorylation of the mutant and the endogenous wild-type STAT1 due to impaired dephosphorylation, indicating heterodimers of the wild-type and mutant STAT1 cause impaired dephosphorylation, as did homodimers of the mutants. Because IL-17A production was not significantly reduced at least in one of the patients following PMA plus ionomycin stimulation, we further studied Th17-associated cytokines IL-17A, IL-17F, and IL-22 in response to more physiologically relevant stimulations. IL-17A and IL-22 production from PBMCs and CD4(+) cells was significantly reduced in four patients with STAT1 GOF mutations, including the previously reported R274Q in response to anti-CD3 plus anti-CD28 Abs or Candida stimulations. In contrast, IL-17F production was comparable to healthy controls in response to anti-CD3 plus anti-CD28 Abs stimulation. These results indicate impaired production of IL-17A and IL-22 rather than IL-17F was associated with the development of CMCD in these patients. Additionally, only the anti-IL-17F autoantibody was detected in sera from 11 of 17 patients with STAT1 GOF mutations, which may be useful as a marker for this disease.

Mendelian susceptibility to mycobacterial disease: genetic, immunological, and clinical features of inborn errors of IFN-γ immunity

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare condition characterized by predisposition to clinical disease caused by weakly virulent mycobacteria, such as BCG vaccines and environmental mycobacteria, in otherwise healthy individuals with no overt abnormalities in routine hematological and immunological tests. MSMD designation does not recapitulate all the clinical features, as patients are also prone to salmonellosis, candidiasis and tuberculosis, and more rarely to infections with other intramacrophagic bacteria, fungi, or parasites, and even, perhaps, a few viruses. Since 1996, nine MSMD-causing genes, including seven autosomal (IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1, ISG15, and IRF8) and two X-linked (NEMO, and CYBB) genes have been discovered. The high level of allelic heterogeneity has already led to the definition of 18 different disorders. The nine gene products are physiologically related, as all are involved in IFN-γ-dependent immunity. These disorders impair the production of (IL12B, IL12RB1, IRF8, ISG15, NEMO) or the response to (IFNGR1, IFNGR2, STAT1, IRF8, CYBB) IFN-γ. These defects account for only about half the known MSMD cases. Patients with MSMD-causing genetic defects may display other infectious diseases, or even remain asymptomatic. Most of these inborn errors do not show complete clinical penetrance for the case-definition phenotype of MSMD. We review here the genetic, immunological, and clinical features of patients with inborn errors of IFN-γ-dependent immunity.