JAK Inhibitor Therapy in a Child with Inherited USP18 Deficiency

Hypersensitivity to type I interferon as a cause of hydrocephalus development

Ubiquitin specific protease 18 (USP18) serves as a potent inhibitor of Type I interferon (IFN) signaling. Previous studies have shown that Usp18 deficient (homozygous Usp18 gene knockout) mice exhibit hydrocephalus; however, the precise molecular mechanism underlying hydrocephalus development remains elusive. In this study, we demonstrate that mice lacking both type I IFN receptor subunit 1 (Ifnar1) and Usp18 (Ifnar1/Usp18 double knockout mice) are viable and do not display a hydrocephalus phenotype. Moreover, we observed that suppression of USP18 in ependymal cells treated with IFN significantly increased cell death, including pyroptosis, and decreased proliferation. These findings suggest that heightened sensitivity to type I IFN during brain development contributes to the onset of hydrocephalus. Furthermore, they imply that inhibition of IFN signaling may hold promise as a therapeutic strategy for hydrocephalus.

Successful treatment of infantile refractory bullous pemphigoid with baricitinib

Infantile bullous pemphigoid (BP) is a rare autoantibody-mediated skin disorder. We report the effective treatment of a 6-month-old infant with BP using baricitinib, a Janus kinase (JAK) inhibitor, after failure with steroids and intravenous immunoglobulin. The patient achieved full remission and discontinued all medications without any relapses. To our knowledge, this is the first case of baricitinib used in an infant with BP.

Broad-spectrum RNA antiviral inspired by ISG15 -/- deficiency

Type I interferons (IFN-I) are cytokines with potent antiviral and inflammatory capacities. IFN-I signaling drives the expression of hundreds of IFN-I stimulated genes (ISGs), whose aggregate function results in the control of viral infection. A few of these ISGs are tasked with negatively regulating the IFN-I response to prevent overt inflammation. ISG15 is a negative regulator whose absence leads to persistent, low-grade elevation of ISG expression and concurrent, self-resolving mild autoinflammation. The limited breadth and low-grade persistence of ISGs expressed in ISG15 deficiency are sufficient to confer broad-spectrum antiviral resistance. Inspired by ISG15 deficiency, we have identified a nominal collection of 10 ISGs that recapitulate the broad antiviral potential of the IFN-I system. The expression of the 10 ISG collection in an IFN-I non-responsive cell line increased cellular resistance to Zika, Vesicular Stomatitis, Influenza A (IAV), and SARS-CoV-2 viruses. A deliverable prophylactic formulation of this syndicate of 10 ISGs significantly inhibited IAV PR8 replication in vivo in mice and protected hamsters against a lethal SARS-CoV-2 challenge, suggesting its potential as a broad-spectrum antiviral against many current and future emerging viral pathogens.

One-Sentence Summary

Human inborn error of immunity-guided discovery and development of a broad-spectrum RNA antiviral therapy.

Macrocephaly and Finger Changes: A Narrative Review

Macrocephaly, characterized by an abnormally large head circumference, often co-occurs with distinctive finger changes, presenting a diagnostic challenge for clinicians. This review aims to provide a current synthetic overview of the main acquired and genetic etiologies associated with macrocephaly and finger changes. The genetic cause encompasses several categories of diseases, including bone marrow expansion disorders, skeletal dysplasias, ciliopathies, inherited metabolic diseases, RASopathies, and overgrowth syndromes. Furthermore, autoimmune and autoinflammatory diseases are also explored for their potential involvement in macrocephaly and finger changes. The intricate genetic mechanisms involved in the formation of cranial bones and extremities are multifaceted. An excess in growth may stem from disruptions in the intricate interplays among the genetic, epigenetic, and hormonal factors that regulate human growth. Understanding the underlying cellular and molecular mechanisms is important for elucidating the developmental pathways and biological processes that contribute to the observed clinical phenotypes. The review provides a practical approach to delineate causes of macrocephaly and finger changes, facilitate differential diagnosis and guide for the appropriate etiological framework. Early recognition contributes to timely intervention and improved outcomes for affected individuals.

Emerging role of immunogenic cell death in cancer immunotherapy

Cancer immunotherapy, such as immune checkpoint blockade (ICB), has emerged as a groundbreaking approach for effective cancer treatment. Despite its considerable potential, clinical studies have indicated that the current response rate to cancer immunotherapy is suboptimal, primarily attributed to low immunogenicity in certain types of malignant tumors. Immunogenic cell death (ICD) represents a form of regulated cell death (RCD) capable of enhancing tumor immunogenicity and activating tumor-specific innate and adaptive immune responses in immunocompetent hosts. Therefore, gaining a deeper understanding of ICD and its evolution is crucial for developing more effective cancer therapeutic strategies. This review focuses exclusively on both historical and recent discoveries related to ICD modes and their mechanistic insights, particularly within the context of cancer immunotherapy. Our recent findings are also highlighted, revealing a mode of ICD induction facilitated by atypical interferon (IFN)-stimulated genes (ISGs), including polo-like kinase 2 (PLK2), during hyperactive type I IFN signaling. The review concludes by discussing the therapeutic potential of ICD, with special attention to its relevance in both preclinical and clinical settings within the field of cancer immunotherapy.

Type I interferon regulation by USP18 is a key vulnerability in cancer

Precise regulation of Type I interferon signaling is crucial for combating infection and cancer while avoiding autoimmunity. Type I interferon signaling is negatively regulated by USP18. USP18 cleaves ISG15, an interferon-induced ubiquitin-like modification, via its canonical catalytic function, and inhibits Type I interferon receptor activity through its scaffold role. USP18 loss-of-function dramatically impacts immune regulation, pathogen susceptibility, and tumor growth. However, prior studies have reached conflicting conclusions regarding the relative importance of catalytic versus scaffold function. Here, we develop biochemical and cellular methods to systematically define the physiological role of USP18. By comparing a patient-derived mutation impairing scaffold function (I60N) to a mutation disrupting catalytic activity (C64S), we demonstrate that scaffold function is critical for cancer cell vulnerability to Type I interferon. Surprisingly, we discovered that human USP18 exhibits minimal catalytic activity, in stark contrast to mouse USP18. These findings resolve human USP18's mechanism-of-action and enable USP18-targeted therapeutics.

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

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

ISG15-USP18 Dysregulation by Oxidative Stress Promotes IFN-γ Secretion from CD8+ T Cells in Vitiligo

Excessive oxidative stress is thought to play pathologic roles in cellular senescence and autoimmune disorders by inducing inflammation and breaking down immune tolerance. In this study, we sought to identify the factors linking oxidative stress to autoimmunity and cellular senescence in vitiligo, where elevated oxidative stress plays an important role. RNA sequencing analysis of hydrogen peroxide-treated melanocytes revealed upregulation of ISG15. The upregulation of ISG15 was observed in vitiligo skin tissues as well as in the blood of patients with vitiligo, whereas USP18 downregulation was observed in vitiligo melanocytes and vitiligo skin tissues. Oxidative stress induced hypermethylation of the USP18 promoter region in keratinocytes and melanocytes, and USP18 promoter hypermethylation was also confirmed in vitiligo skin tissues. Our results indicate that USP18 promoter hypermethylation caused by oxidative stress increases ISG15 expression in keratinocytes and melanocytes along with senescence changes, leading CD8+ T cells to produce IFN-γ, the main pathogenic cytokine in vitiligo. Therefore, the ISG15-USP18 network may be important in oxidative stress-induced autoimmunity and cellular senescence in vitiligo pathogenesis.

Selectivity, efficacy and safety of JAKinibs: new evidence for a still evolving story

Fundamental insight gained over the last decades led to the discovery of cytokines as pivotal drivers of inflammatory diseases such as rheumatoid arthritis, psoriasis/psoriasis arthritis, inflammatory bowel diseases, atopic dermatitis and spondylarthritis. A deeper understanding of the pro-inflammatory and anti-inflammatory effects of various cytokines has prompted new cytokine-targeting therapies, which revolutionised the treatment options in the last years for patients with inflammatory disorders. Disease-associated immune responses typically involve a complex interplay of multiple cytokines. Therefore, blockade of one single cytokine does not necessarily lead to a persistent remission in all patients with inflammatory disorders and fostered new therapeutic strategies targeting intracellular pathways shared by multiple cytokines. By inhibiting JAK-STAT signalling pathways common to families of cytokines, JAK-inhibitors (JAKinibs) have created a new paradigm for the treatment of inflammatory diseases. Multiple agents have been approved for various disorders and more are being investigated for several new indications. Second-generation selective JAKinibs have been devised with the aim to achieve an increased selectivity and a possible reduced risk of side effects. In the current review, we will summarise the current body of evidence of pan versus selective JAKinibs and the most recent insights on new side effects and indications, including COVID-19.

Interferon-α receptor antisense oligonucleotides reduce neuroinflammation and neuropathology in a mouse model of cerebral interferonopathy

Chronic and elevated levels of the antiviral cytokine IFN-α in the brain are neurotoxic. This is best observed in patients with genetic cerebral interferonopathies such as Aicardi-Goutières syndrome. Cerebral interferonopathies typically manifest in early childhood and lead to debilitating disease and premature death. There is no cure for these diseases with existing treatments largely aimed at managing symptoms. Thus, an effective therapeutic strategy is urgently needed. Here, we investigated the effect of antisense oligonucleotides targeting the murine IFN-α receptor (Ifnar1 ASOs) in a transgenic mouse model of cerebral interferonopathy. Intracerebroventricular injection of Ifnar1 ASOs into transgenic mice with brain-targeted chronic IFN-α production resulted in a blunted cerebral interferon signature, reduced neuroinflammation, restoration of blood-brain barrier integrity, absence of tissue destruction, and lessened neuronal damage. Remarkably, Ifnar1 ASO treatment was also effective when given after the onset of neuropathological changes, as it reversed such disease-related features. We conclude that ASOs targeting the IFN-α receptor halt and reverse progression of IFN-α-mediated neuroinflammation and neurotoxicity, opening what we believe to be a new and promising approach for the treatment of patients with cerebral interferonopathies.

JAK inhibitor treatment for inborn errors of JAK/STAT signaling: An ESID/EBMT-IEWP retrospective study

BACKGROUND

Inborn errors of immunity (IEI) with dysregulated JAK/STAT signaling present with variable manifestations of immune dysregulation and infections. Hematopoietic stem cell transplantation (HSCT) is potentially curative, but initially reported outcomes were poor. JAK inhibitors (JAKi) offer a targeted treatment option that may be an alternative or bridge to HSCT. However, data on their current use, treatment efficacy and adverse events are limited.

OBJECTIVE

We evaluated the current off-label JAKi treatment experience for JAK/STAT inborn errors of immunity (IEI) among European Society for Immunodeficiencies (ESID)/European Society for Blood and Marrow Transplantation (EBMT) Inborn Errors Working Party (IEWP) centers.

METHODS

We conducted a multicenter retrospective study on patients with a genetic disorder of hyperactive JAK/STAT signaling who received JAKi treatment for at least 3 months.

RESULTS

Sixty-nine patients (72% children) were evaluated (45 STAT1 gain of function [GOF], 21 STAT3-GOF, 1 STAT5B-GOF, 1 suppressor of cytokine signaling 1 [aka SOCS1] loss of function, 1 JAK1-GOF). Ruxolitinib was the predominantly prescribed JAKi (80%). Overall, treatment resulted in improvement (partial or complete remission) of clinical symptoms in 87% of STAT1-GOF and in 90% of STAT3-GOF patients. We documented highly heterogeneous dosing and monitoring regimens. The response rate and time to response varied across different diseases and manifestations. Adverse events including infection and weight gain were frequent (38% of patients) but were mild (grade I-II) and transient in most patients. At last follow-up, 52 (74%) of 69 patients were still receiving JAKi treatment, and 11 patients eventually underwent HSCT after receipt of previous JAKi bridging therapy, with 91% overall survival.

CONCLUSIONS

Our study suggests that JAKi may be highly effective to treat symptomatic JAK/STAT IEI patients. Prospective studies to define optimal JAKi dosing for the variable clinical presentations and age ranges should be pursued.

The Impact of Innate Components on Viral Pathogenesis in the Neurotropic Coronavirus Encephalomyelitis Mouse Model

Recognition of viruses invading the central nervous system (CNS) by pattern recognition receptors (PRRs) is crucial to elicit early innate responses that stem dissemination. These innate responses comprise both type I interferon (IFN-I)-mediated defenses as well as signals recruiting leukocytes to control the infection. Focusing on insights from the neurotropic mouse CoV model, this review discusses how early IFN-I, fibroblast, and myeloid signals can influence protective anti-viral adaptive responses. Emphasis is placed on three main areas: the importance of coordinating the distinct capacities of resident CNS cells to induce and respond to IFN-I, the effects of select IFN-stimulated genes (ISGs) on host immune responses versus viral control, and the contribution of fibroblast activation and myeloid cells in aiding the access of T cells to the parenchyma. By unraveling how the dysregulation of early innate components influences adaptive immunity and viral control, this review illustrates the combined effort of resident CNS cells to achieve viral control.

Case Report: ISG15 deficiency caused by novel variants in two families and effective treatment with Janus kinase inhibition

ISG15 deficiency is a rare disease caused by autosomal recessive variants in the ISG15 gene, which encodes the ISG15 protein. The ISG15 protein plays a dual role in both the type I and II interferon (IFN) immune pathways. Extracellularly, the ISG15 protein is essential for IFN-γ-dependent anti-mycobacterial immunity, while intracellularly, ISG15 is necessary for USP18-mediated downregulation of IFN-α/β signalling. Due to this dual role, ISG15 deficiency can present with various clinical phenotypes, ranging from susceptibility to mycobacterial infection to autoinflammation characterised by necrotising skin lesions, intracerebral calcification, and pulmonary involvement. In this report, we describe novel variants found in two different families that result in complete ISG15 deficiency and severe skin ulceration. Whole exome sequencing identified a heterozygous missense p.Q16X ISG15 variant and a heterozygous multigene 1p36.33 deletion in the proband from the first family. In the second family, a homozygous total ISG15 gene deletion was detected in two siblings. We also conducted further analysis, including characterisation of cytokine dysregulation, interferon-stimulated gene expression, and p-STAT1 activation in lymphocytes and lesional tissue. Finally, we demonstrate the complete and rapid resolution of clinical symptoms associated with ISG15 deficiency in one sibling from the second family following treatment with the Janus kinase (JAK) inhibitor baricitinib.

A novel homozygous Y140X mutation of ISG15 causes diverse type I interferonopathies in sibling patients with cutaneous lesions or recurrent parenchymal pneumonia

PURPOSE

Interferon-stimulated gene 15 (ISG15) deficiency, a rare human inborn error of immunity characterized by susceptibility to Bacillus Calmette-Guerin (BCG) diseases, neuropathic and dermatological manifestations.

METHODS

The clinical and immunological features of two siblings with ISG15 deficiency combined with asymptomatic myeloperoxidase (MPO) mutations were analyzed, and their pathogenesis, as well as target therapeutic candidates, were explored.

RESULTS

The manifestation in patient 2 was skin lesions, while those in patient 1 were intracranial calcification and recurrent pneumonia. Whole-exome identified novel, dual mutations in ISG15 and MPO. PBMCs and B cell lines derived from the patients showed hyper-activated JAK/STAT signaling. Normal neutrophil function excluded pathogenicity caused by the MPO mutation. RNA sequencing identified baricitinib as therapeutic candidate.

CONCLUSIONS

We report two sibling patients harboring the same novel ISG15 mutation showing diverse clinical features, and one harbored a rare phenotype of pneumonia. These findings expand the clinical spectrum of ISG15 deficiency and identify baricitinib as therapeutic candidate.

How to Build a Fire: The Genetics of Autoinflammatory Diseases

Systemic autoinflammatory diseases (SAIDs) are a heterogeneous group of disorders caused by excess activation of the innate immune system in an antigen-independent manner. Starting with the discovery of the causal gene for familial Mediterranean fever, more than 50 monogenic SAIDs have been described. These discoveries, paired with advances in immunology and genomics, have allowed our understanding of these diseases to improve drastically in the last decade. The genetic causes of SAIDs are complex and include both germline and somatic pathogenic variants that affect various inflammatory signaling pathways. We provide an overview of the acquired SAIDs from a genetic perspective and summarize the clinical phenotypes and mechanism(s) of inflammation, aiming to provide a comprehensive understanding of the pathogenesis of autoinflammatory diseases.

Type I Interferonopathies: A Clinical Review

This review will discuss when clinicians should consider evaluating for Type I interferonopathies, review clinical phenotypes and molecular defects of Type I interferonopathies, and discuss current treatments.

Deficiencies and Dysregulation of STAT Pathways That Drive Inborn Errors of Immunity: Lessons from Patients and Mouse Models of Disease

The STAT family proteins provide critical signals for immune cell development, differentiation, and proinflammatory and anti-inflammatory responses. Inborn errors of immunity (IEIs) are caused by single gene defects leading to immune deficiency and/or dysregulation, and they have provided opportunities to identify genes important for regulating the human immune response. Studies of patients with IEIs due to altered STAT signaling, and mouse models of these diseases, have helped to shape current understanding of the mechanisms whereby STAT signaling and protein interactions regulate immunity. Although many STAT signaling pathways are shared, clinical and immune phenotypes in patients with monogenic defects of STAT signaling highlight both redundant and nonredundant pathways. In this review, we provide an overview of the shared and unique signaling pathways used by STATs, phenotypes of IEIs with altered STAT signaling, and recent discoveries that have provided insight into the human immune response and treatment of disease.

USP18 is an essential regulator of muscle cell differentiation and maturation

The ubiquitin proteasomal system is a critical regulator of muscle physiology, and impaired UPS is key in many muscle pathologies. Yet, little is known about the function of deubiquitinating enzymes (DUBs) in the muscle cell context. We performed a genetic screen to identify DUBs as potential regulators of muscle cell differentiation. Surprisingly, we observed that the depletion of ubiquitin-specific protease 18 (USP18) affected the differentiation of muscle cells. USP18 depletion first stimulated differentiation initiation. Later, during differentiation, the absence of USP18 expression abrogated myotube maintenance. USP18 enzymatic function typically attenuates the immune response by removing interferon-stimulated gene 15 (ISG15) from protein substrates. However, in muscle cells, we found that USP18, predominantly nuclear, regulates differentiation independent of ISG15 and the ISG response. Exploring the pattern of RNA expression profiles and protein networks whose levels depend on USP18 expression, we found that differentiation initiation was concomitant with reduced expression of the cell-cycle gene network and altered expression of myogenic transcription (co) factors. We show that USP18 depletion altered the calcium channel gene network, resulting in reduced calcium flux in myotubes. Additionally, we show that reduced expression of sarcomeric proteins in the USP18 proteome was consistent with reduced contractile force in an engineered muscle model. Our results revealed nuclear USP18 as a critical regulator of differentiation initiation and maintenance, independent of ISG15 and its role in the ISG response.

Breaking down the cellular responses to type I interferon neurotoxicity in the brain

Since their original discovery, type I interferons (IFN-Is) have been closely associated with antiviral immune responses. However, their biological functions go far beyond this role, with balanced IFN-I activity being critical to maintain cellular and tissue homeostasis. Recent findings have uncovered a darker side of IFN-Is whereby chronically elevated levels induce devastating neuroinflammatory and neurodegenerative pathologies. The underlying causes of these 'interferonopathies' are diverse and include monogenetic syndromes, autoimmune disorders, as well as chronic infections. The prominent involvement of the CNS in these disorders indicates a particular susceptibility of brain cells to IFN-I toxicity. Here we will discuss the current knowledge of how IFN-Is mediate neurotoxicity in the brain by analyzing the cell-type specific responses to IFN-Is in the CNS, and secondly, by exploring the spectrum of neurological disorders arising from increased IFN-Is. Understanding the nature of IFN-I neurotoxicity is a crucial and fundamental step towards development of new therapeutic strategies for interferonopathies.

Unlocking life-threatening COVID-19 through two types of inborn errors of type I IFNs

Since 2003, rare inborn errors of human type I IFN immunity have been discovered, each underlying a few severe viral illnesses. Autoantibodies neutralizing type I IFNs due to rare inborn errors of autoimmune regulator (AIRE)-driven T cell tolerance were discovered in 2006, but not initially linked to any viral disease. These two lines of clinical investigation converged in 2020, with the discovery that inherited and/or autoimmune deficiencies of type I IFN immunity accounted for approximately 15%-20% of cases of critical COVID-19 pneumonia in unvaccinated individuals. Thus, insufficient type I IFN immunity at the onset of SARS-CoV-2 infection may be a general determinant of life-threatening COVID-19. These findings illustrate the unpredictable, but considerable, contribution of the study of rare human genetic diseases to basic biology and public health.

Expansion of interferon inducible gene pool via USP18 inhibition promotes cancer cell pyroptosis

While immunotherapy has emerged as a breakthrough cancer therapy, it is only effective in some patients, indicating the need of alternative therapeutic strategies. Induction of cancer immunogenic cell death (ICD) is one promising way to elicit potent adaptive immune responses against tumor-associated antigens. Type I interferon (IFN) is well known to play important roles in different aspects of immune responses, including modulating ICD in anti-tumor action. However, how to expand IFN effect in promoting ICD responses has not been addressed. Here we show that depletion of ubiquitin specific protease 18 (USP18), a negative regulator of IFN signaling, selectively induces cancer cell ICD. Lower USP18 expression correlates with better survival across human selected cancer types and delays cancer progression in mouse models. Mechanistically, nuclear USP18 controls the enhancer landscape of cancer cells and diminishes STAT2-mediated transcription complex binding to IFN-responsive elements. Consequently, USP18 suppression not only enhances expression of canonical IFN-stimulated genes (ISGs), but also activates the expression of a set of atypical ISGs and NF-κB target genes, including genes such as Polo like kinase 2 (PLK2), that induce cancer pyroptosis. These findings may support the use of targeting USP18 as a potential cancer immunotherapy.

Mendelian susceptibility to mycobacterial disease: an overview

Background

Mycobacteria include ubiquitous species of varying virulence. However, environmental and individual-specific factors, particularly host genetics, play a crucial role in the outcome of exposure to mycobacteria. The first molecular evidence of a monogenic predisposition to mycobacteria came from the study of Mendelian susceptibility to mycobacterial disease (MSMD), a rare inborn error of IFN-γ immunity conferring a selective susceptibility to infections even with low virulent mycobacteria, in patients, mostly children, without recognizable immune defects in routine tests. This article provides a global and updated description of the most important molecular, cellular, and clinical features of all known monogenic defects of MSMD.

Results

Over the last 20 years, 19 genes were found to be mutated in MSMD patients (IFNGR1, IFNGR2, IFNG, IL12RB1, IL12RB2, IL23R, IL12B, ISG15, USP18, ZNFX1, TBX21, STAT1, TYK2, IRF8, CYBB, JAK1, RORC, NEMO, and SPPL2A), and the allelic heterogeneity at these loci has led to the definition of 35 different genetic defects. Despite the clinical and genetic heterogeneity, almost all genetic etiologies of MSMD alter the interferon gamma (IFN-γ)-mediated immunity, by impairing or abolishing IFN-γ production or the response to this cytokine or both. It was proven that the human IFN-γ level is a quantitative trait that defines the outcome of mycobacterial infection.

Conclusion

The study of these monogenic defects contributes to understanding the molecular mechanism of mycobacterial infections in humans and to the development of new diagnostic and therapeutic approaches to improve care and prognosis. These discoveries also bridge the gap between the simple Mendelian inheritance and complex human genetics.

A mixed-method analysis to identify the current focus, trends, and gaps in health science research in Saudi Arabia

Background

The identification of current gaps in high-impact medical research in Saudi Arabia has international significance due to the trend of collaborative research in the field of health and medicine and the focus on knowledge-sharing. The purpose of this study is to assess the current focus, gaps, and priorities in health research in Saudi Arabia.

Methods

We employed a mixed-method research approach to achieve research objectives. (1) a systematic review of scientific research studies that are published between January 2020 to January 2022 in the top fifty Q1 medical science journals (2) a cross-sectional survey collected data from professionals employed in various organizations including the Ministry of Health (MoH), Ministry of Education (MoE), health organizations and universities, and the health industry. The close-ended survey questions inquired about the broad and specific areas of ongoing health research projects by these researchers and organizations in Saudi Arabia.

Results

The literature search on databases identified Science Direct (n = 741), Pub Med (n = 244) and Google Scholar (n = 15,600). After screening, (n = 26) original studies were selected for detailed evaluation and synthesis. Among these (n = 7) studied infectious diseases, (n = 7) cancer, and cardiac disease (n = 5). These studies focused on the etiology, treatment management and therapy outcomes of these health conditions. The survey was completed by (n = 384) respondents from these organizations. Most of the ongoing research projects focus on clinical sciences (27%) followed by basic sciences (24%) and public health research (24%) and a limited number of researchers were involved in healthcare management (2%) and informatics (2%). Most research focused on kidney and liver disorders (80%), obesity (74%), diabetes (74%), hormonal diseases (64%), and infectious disease (66%); it is equally important to design and fund research in some of the neglected areas including reproductive health (3%), physical and mental disabilities (1%).

Conclusion

Findings suggest that current gaps in original research from Saudi Arabia are in healthcare service quality, reproductive health, physical and mental disabilities and health informatics. Researchers and funding agencies and international collaborative projects should prioritize these areas.

CLEC16A interacts with retromer and TRIM27, and its loss impairs endosomal trafficking and neurodevelopment

CLEC16A is a membrane-associated C-type lectin protein that functions as a E3-ubiquitin ligase. CLEC16A regulates autophagy and mitophagy, and reportedly localizes to late endosomes. GWAS studies have associated CLEC16A SNPs to various auto-immune and neurological disorders, including multiple sclerosis and Parkinson disease. Studies in mouse models imply a role for CLEC16A in neurodegeneration. We identified bi-allelic CLEC16A truncating variants in siblings from unrelated families presenting with a severe neurodevelopmental disorder including microcephaly, brain atrophy, corpus callosum dysgenesis, and growth retardation. To understand the function of CLEC16A in neurodevelopment we used in vitro models and zebrafish embryos. We observed CLEC16A localization to early endosomes in HEK293T cells. Mass spectrometry of human CLEC16A showed interaction with endosomal retromer complex subunits and the endosomal ubiquitin ligase TRIM27. Expression of the human variant leading to C-terminal truncated CLEC16A, abolishes both its endosomal localization and interaction with TRIM27, suggesting a loss-of-function effect. CLEC16A knockdown increased TRIM27 adhesion to early endosomes and abnormal accumulation of endosomal F-actin, a sign of disrupted vesicle sorting. Mutagenesis of clec16a by CRISPR-Cas9 in zebrafish embryos resulted in accumulated acidic/phagolysosome compartments, in neurons and microglia, and dysregulated mitophagy. The autophagocytic phenotype was rescued by wild-type human CLEC16A but not the C-terminal truncated CLEC16A. Our results demonstrate that CLEC16A closely interacts with retromer components and regulates endosomal fate by fine-tuning levels of TRIM27 and polymerized F-actin on the endosome surface. Dysregulation of CLEC16A-mediated endosomal sorting is associated with neurodegeneration, but it also causes accumulation of autophagosomes and unhealthy mitochondria during brain development.

ISG15 driven cellular responses to virus infection

One of the hallmarks of antiviral responses to infection is the production of interferons and subsequently of interferon stimulated genes. Interferon stimulated gene 15 (ISG15) is among the earliest and most abundant proteins induced upon interferon signalling, encompassing versatile functions in host immunity. ISG15 is a ubiquitin like modifier that can be conjugated to substrates in a process analogous to ubiquitylation and referred to as ISGylation. The free unconjugated form can either exist intracellularly or be secreted to function as a cytokine. Interestingly, ISG15 has been reported to be both advantageous and detrimental to the development of immunopathology during infection. This review describes recent findings on the role of ISG15 in antiviral responses in human infection models, with a particular emphasis on autophagy, inflammatory responses and cellular metabolism combined with viral strategies of counteracting them. The field of ISGylation has steadily gained momentum; however much of the previous studies of virus infections conducted in mouse models are in sharp contrast with recent findings in human cells, underscoring the need to summarise our current understanding of its potential antiviral function in humans and identify knowledge gaps which need to be addressed in future studies.

Excessive negative regulation of type I interferon disrupts viral control in individuals with Down syndrome

Down syndrome (DS) is typically caused by triplication of chromosome 21. Phenotypically, DS presents with developmental, neurocognitive, and immune features. Epidemiologically, individuals with DS have less frequent viral infection, but when present, these infections lead to more severe disease. The potent antiviral cytokine type I Interferon (IFN-I) receptor subunits IFNAR1 and IFNAR2 are located on chromosome 21. While increased IFNAR1/2 expression initially caused hypersensitivity to IFN-I, it triggered excessive negative feedback. This led to a hypo-response to subsequent IFN-I stimuli and an ensuing viral susceptibility in DS compared to control cells. Upregulation of IFNAR2 expression phenocopied the DS IFN-I dynamics independent of trisomy 21. CD14+ monocytes from individuals with DS exhibited markers of prior IFN-I exposure and had muted responsiveness to ex vivo IFN-I stimulation. Our findings unveil oscillations of hyper- and hypo-response to IFN-I in DS, predisposing individuals to both lower incidence of viral disease and increased infection-related morbidity and mortality.

The DUB Club: Deubiquitinating Enzymes and Neurodevelopmental Disorders

Protein ubiquitination is a widespread, multifunctional, posttranslational protein modification, best known for its ability to direct protein degradation via the ubiquitin proteasome system (UPS). Ubiquitination is also reversible, and the human genome encodes over 90 deubiquitinating enzymes (DUBs), many of which appear to target specific subsets of ubiquitinated proteins. This review focuses on the roles of DUBs in neurodevelopmental disorders (NDDs). We present the current genetic evidence connecting 12 DUBs to a range of NDDs and the functional studies implicating at least 19 additional DUBs as candidate NDD genes. We highlight how the study of DUBs in NDDs offers critical insights into the role of protein degradation during brain development. Because one of the major known functions of a DUB is to antagonize the UPS, loss of function of DUB genes has been shown to culminate in loss of abundance of its protein substrates. The identification and study of NDD DUB substrates in the developing brain is revealing that they regulate networks of proteins that themselves are encoded by NDD genes. We describe the new technologies that are enabling the full resolution of DUB protein networks in the developing brain, with the view that this knowledge can direct the development of new therapeutic paradigms. The fact that the abundance of many NDD proteins is regulated by the UPS presents an exciting opportunity to combat NDDs caused by haploinsufficiency, because the loss of abundance of NDD proteins can be potentially rectified by antagonizing their UPS-based degradation.

The JAK-STAT pathway at 30: Much learned, much more to do

The discovery of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway arose from investigations of how cells respond to interferons (IFNs), revealing a paradigm in cell signaling conserved from slime molds to mammals. These discoveries revealed mechanisms underlying rapid gene expression mediated by a wide variety of extracellular polypeptides including cytokines, interleukins, and related factors. This knowledge has provided numerous insights into human disease, from immune deficiencies to cancer, and was rapidly translated to new drugs for autoimmune, allergic, and infectious diseases, including COVID-19. Despite these advances, major challenges and opportunities remain.

E3 ubiquitin ligase MID1 ubiquitinates and degrades type-I interferon receptor 2

Type I interferon (IFN-I) is a common biological molecule used for the treatment of viral diseases. However, the clinical antiviral efficacy of IFN-I needs to be greatly improved. In this study, IFN-I receptor 2 (IFNAR2) was revealed to undergo degradation at the protein level in cells treated with IFN-I for long periods of time. Further studies found a physical interaction between the E3 ubiquitin ligase Midline-1 (MID1) and IFNAR2. As a consequence, MID1 induced both K48-linked and K63-linked polyubiquitination of IFNAR2, which promoted IFNAR2 protein degradation in a lysosome-dependent manner. Conversely, knockdown of MID1 largely restricted IFN-I-induced degradation of IFNAR2. Importantly, MID1 regulated the strength of IFN-I signaling and IFN-I-induced antiviral activity. These findings reveal a regulatory mechanism of IFNAR2 ubiquitination and protein stability in IFN-I signaling, which could provide a potential target for improving the antiviral efficacy of IFN-I.

A partial form of inherited human USP18 deficiency underlies infection and inflammation

Human USP18 is an interferon (IFN)-stimulated gene product and a negative regulator of type I IFN (IFN-I) signaling. It also removes covalently linked ISG15 from proteins, in a process called deISGylation. In turn, ISG15 prevents USP18 from being degraded by the proteasome. Autosomal recessive complete USP18 deficiency is life-threatening in infancy owing to uncontrolled IFN-I–mediated autoinflammation. We report three Moroccan siblings with autoinflammation and mycobacterial disease who are homozygous for a new USP18 variant. We demonstrate that the mutant USP18 (p.I60N) is normally stabilized by ISG15 and efficient for deISGylation but interacts poorly with the receptor-anchoring STAT2 and is impaired in negative regulation of IFN-I signaling. We also show that IFN-γ–dependent induction of IL-12 and IL-23 is reduced owing to IFN-I–mediated impairment of myeloid cells to produce both cytokines. Thus, insufficient negative regulation of IFN-I signaling by USP18-I60N underlies a specific type I interferonopathy, which impairs IL-12 and IL-23 production by myeloid cells, thereby explaining predisposition to mycobacterial disease.

[When to consider type I interferonopathy in adulthood?]

Type I interferonopathies (IP1) are a heterogeneous group of Mendelian diseases characterized by overactivation of the type I interferon (IFN) pathway. They are caused by monogenic (rarely digenic) mutations of proteins involved in this key pathway of innate immunity. IP1 transmission can be dominant, recessive or X-linked and penetrance differs from one IP1 to another. The clinical spectrum is broad and mainly includes central nervous system involvement with calcifications of the basal ganglia, skin disorders such as cutaneous vasculitis that can be mutilating. Joint disorders including non-destructive deforming arthropathy, pulmonary involvement such as intra-alveolar haemorrhage or interstitial lung disease, and haematological symptoms with cytopenia and/or immune deficiency are also seen. The clinical manifestations vary from one IP1 to another and their spectrum is constantly expanding along with the description of new IP1s and patients. The inflammatory syndrome is generally mild and autoimmune stigmata are frequently found. Almost all patients display overexpression of the type I IFN pathway detected, for instance, by the evaluation of IFN-stimulated genes expression, referred as "interferon signature". The related morbidity and mortality are high. However, the beneficial effect on certain symptoms of targeted therapies inhibiting type I IFN, such as JAK inhibitors, has led to a promising improvement in the management of these patients.

Neuroinflammation Associated With Inborn Errors of Immunity

The advent of high-throughput sequencing has facilitated genotype-phenotype correlations in congenital diseases. This has provided molecular diagnosis and benefited patient management but has also revealed substantial phenotypic heterogeneity. Although distinct neuroinflammatory diseases are scarce among the several thousands of established congenital diseases, elements of neuroinflammation are increasingly recognized in a substantial proportion of inborn errors of immunity, where it may even dominate the clinical picture at initial presentation. Although each disease entity is rare, they collectively can constitute a significant proportion of neuropediatric patients in tertiary care and may occasionally also explain adult neurology patients. We focus this review on the signs and symptoms of neuroinflammation that have been reported in association with established pathogenic variants in immune genes and suggest the following subdivision based on proposed underlying mechanisms: autoinflammatory disorders, tolerance defects, and immunodeficiency disorders. The large group of autoinflammatory disorders is further subdivided into IL-1β-mediated disorders, NF-κB dysregulation, type I interferonopathies, and hemophagocytic syndromes. We delineate emerging pathogenic themes underlying neuroinflammation in monogenic diseases and describe the breadth of the clinical spectrum to support decisions to screen for a genetic diagnosis and encourage further research on a neglected phenomenon.

Case Report: Generalised Panniculitis as a Post-COVID-19 Presentation in Aicardi-Goutières Syndrome Treated With Ruxolitinib

Aicardi-Goutières syndrome (AGS) is a rare hereditary early-onset encephalopathy. The syndrome was first described in 1984, and is characterised by upregulation of the type I interferon (IFN) pathway, which is involved in the host immune response against viral infections, including SARS-CoV-2. Whilst defects in type I IFN pathways have been described in association with severe coronavirus disease 2019 (COVID-19), less is known about the outcomes of upregulation. We describe an unusual case of generalised panniculitis as a post-COVID-19 phenomenon in a child with AGS. Our patient was initially managed with systemic steroid therapy, but due to relapse of symptoms on weaning, an alternative therapy was sought. In this case, a novel use of ruxolitinib, a JAK inhibitor, has resulted in lasting remission without complications. We discuss the probable protective role of IFN upregulation following COVID-19 infection in AGS and possible immunological mechanisms driving the panniculitis and therapeutic response in our case.

Spectrum of Neuroradiologic Findings Associated with Monogenic Interferonopathies

The genetic interferonopathies are a heterogeneous group of disorders thought to be caused by the dysregulated expression of interferons and are now commonly considered in the differential diagnosis of children presenting with recurrent or persistent inflammatory phenotypes. With emerging therapeutic options, recognition of these disorders is increasingly important, and neuroimaging plays a vital role. In this article, we discuss the wide spectrum of neuroradiologic features associated with monogenic interferonopathies by reviewing the literature and illustrate these with cases from our institutions. These cases include intracerebral calcifications, white matter T2 hyperintensities, deep WM cysts, cerebral atrophy, large cerebral artery disease, bilateral striatal necrosis, and masslike lesions. A better understanding of the breadth of the neuroimaging phenotypes in conjunction with clinical and laboratory findings will enable earlier diagnosis and direct therapeutic strategies.

The type I interferonopathies: 10 years on

As brutally demonstrated by the COVID-19 pandemic, an effective immune system is essential for survival. Developed over evolutionary time, viral nucleic acid detection is a central pillar in the defensive armamentarium used to combat foreign microbial invasion. To ensure cellular homeostasis, such a strategy necessitates the efficient discrimination of pathogen-derived DNA and RNA from that of the host. In 2011, it was suggested that an upregulation of type I interferon signalling might serve as a defining feature of a novel set of Mendelian inborn errors of immunity, where antiviral sensors are triggered by host nucleic acids due to a failure of self versus non-self discrimination. These rare disorders have played a surprisingly significant role in informing our understanding of innate immunity and the relevance of type I interferon signalling for human health and disease. Here we consider what we have learned in this time, and how the field may develop in the future.

Novel Genetic Discoveries in Primary Immunodeficiency Disorders

The field of Immunology is one that has undergone great expansion in recent years. With the advent of new diagnostic modalities including a variety of genetic tests (discussed elsewhere in this journal), the ability to diagnose a patient with a primary immunodeficiency disorder (PIDD) has become a more streamlined process. With increased availability of genetic testing for those with suspected or known PIDD, there has been a significant increase in the number of genes associated with this group of disorders. This is of great importance as a misdiagnosis of these rare diseases can lead to a delay in what can be critical treatment options. At times, those options can include life-saving medications or procedures. Presentation of patients with PIDD can vary greatly based on the specific genetic defect and the part(s) of the immune system that is affected by the variation. PIDD disorders lead to varying levels of increased risk of infection ranging from a mild increase such as with selective IgA deficiency to a profound risk with severe combined immunodeficiency. These diseases can also cause a variety of other clinical findings including autoimmunity and gastrointestinal disease.

Congenital deficiency reveals critical role of ISG15 in skin homeostasis

Ulcerating skin lesions are manifestations of human ISG15 deficiency, a type I interferonopathy. However, chronic inflammation may not be their exclusive cause. We describe two siblings with recurrent skin ulcers that healed with scar formation upon corticosteroid treatment. Both had a homozygous nonsense mutation in the ISG15 gene, leading to unstable ISG15 protein lacking the functional domain. We characterized ISG15^–/– dermal fibroblasts, HaCaT keratinocytes, and human induced pluripotent stem cell–derived vascular endothelial cells. ISG15-deficient cells exhibited the expected hyperinflammatory phenotype, but also dysregulated expression of molecules critical for connective tissue and epidermis integrity, including reduced collagens and adhesion molecules, but increased matrix metalloproteinases. ISG15^–/– fibroblasts exhibited elevated ROS levels and reduced ROS scavenger expression. As opposed to hyperinflammation, defective collagen and integrin synthesis was not rescued by conjugation-deficient ISG15. Cell migration was retarded in ISG15^–/– fibroblasts and HaCaT keratinocytes, but normalized under ruxolitinib treatment. Desmosome density was reduced in an ISG15^–/– 3D epidermis model. Additionally, there were loose architecture and reduced collagen and desmoglein expression, which could be reversed by treatment with ruxolitinib/doxycycline/TGF-β1. These results reveal critical roles of ISG15 in maintaining cell migration and epidermis and connective tissue homeostasis, whereby the latter likely requires its conjugation to yet unidentified targets.

An Integrated View of Deubiquitinating Enzymes Involved in Type I Interferon Signaling, Host Defense and Antiviral Activities

Viral infectious diseases pose a great challenge to human health around the world. Type I interferons (IFN-Is) function as the first line of host defense and thus play critical roles during virus infection by mediating the transcriptional induction of hundreds of genes. Nevertheless, overactive cytokine immune responses also cause autoimmune diseases, and thus, tight regulation of the innate immune response is needed to achieve viral clearance without causing excessive immune responses. Emerging studies have recently uncovered that the ubiquitin system, particularly deubiquitinating enzymes (DUBs), plays a critical role in regulating innate immune responses. In this review, we highlight recent advances on the diverse mechanisms of human DUBs implicated in IFN-I signaling. These DUBs function dynamically to calibrate host defenses against various virus infections by targeting hub proteins in the IFN-I signaling transduction pathway. We also present a future perspective on the roles of DUB-substrate interaction networks in innate antiviral activities, discuss the promises and challenges of DUB-based drug development, and identify the open questions that remain to be clarified. Our review provides a comprehensive description of DUBs, particularly their differential mechanisms that have evolved in the host to regulate IFN-I-signaling-mediated antiviral responses.

JAK-STAT signaling in human disease: From genetic syndromes to clinical inhibition

Since its discovery, the Janus kinase-signal transduction and activation of transcription (JAK-STAT) pathway has become recognized as a central mediator of widespread and varied human physiological processes. The field of JAK-STAT biology, particularly its clinical relevance, continues to be shaped by 2 important advances. First, the increased use of genomic sequencing has led to the discovery of novel clinical syndromes caused by mutations in JAK and STAT genes. This has provided insights regarding the consequences of aberrant JAK-STAT signaling for immunity, lymphoproliferation, and malignancy. In addition, since the approval of ruxolitinib and tofacitinib, the therapeutic use of JAK inhibitors (jakinibs) has expanded to include a large spectrum of diseases. Efficacy and safety data from over a decade of clinical studies have provided additional mechanistic insights while improving the care of patients with inflammatory and neoplastic conditions. This review discusses major advances in the field, focusing on updates in genetic diseases and in studies of clinical jakinibs in human disease.

The JAK2 inhibitor TG101209 exhibits anti-tumor and chemotherapeutic sensitizing effects on Burkitt lymphoma cells by inhibiting the JAK2/STAT3/c-MYB signaling axis

Constitutive activation of JAK2/STAT3 is a major oncogenic signaling event involved in the development of Burkitt lymphoma (BL). In the present study, we investigated the antilymphoma activity of TG101209, a specific JAK2 inhibitor, on EBV-positive and EBV-negative Burkitt lymphoma cell lines and primary BL cells. The results showed that TG101209 had a significant antilymphoma effect by inhibiting BL cell growth and inducing apoptosis along with cell differentiation toward mature B cells in vitro. We also found that TG101209 displayed significant synergistic action and a sensitizing effect on the anti-Burkitt lymphoma activity of doxorubicin. In vivo experiments indicated that TG101209 could suppress tumor growth and prolong the overall survival of BL cell-bearing mice. The mechanistic study indicated that TG101209, by suppressing the JAK2/STAT3/c-MYB signaling axis and crosstalk between the downstream signaling pathways, plays an antilymphoma role. These data suggested that TG101209 may be a promising agent or alternative choice for the treatment of BL.

Emerging Place of JAK Inhibitors in the Treatment of Inborn Errors of Immunity

Among inborn errors of immunity (IEIs), some conditions are characterized by inflammation and autoimmunity at the front line and are particularly challenging to treat. Monogenic diseases associated with gain-of-function mutations in genes critical for cytokine signaling through the JAK-STAT pathway belong to this group. These conditions represent good candidates for treatment with JAK inhibitors. Type I interferonopathies, a group of recently identified monogenic auto-inflammatory diseases characterized by excessive secretion of type I IFN, are also good candidates with growing experiences reported in the literature. However, many questions remain regarding the choice of the drug, the dose (in particular in children), the efficacy on the various manifestations, the monitoring of the treatment, and the management of potent side effects in particular in patients with infectious susceptibility. This review will summarize the current experiences reported and will highlight the unmet needs.

Human Disease Phenotypes Associated with Loss and Gain of Function Mutations in STAT2: Viral Susceptibility and Type I Interferonopathy

STAT2 is distinguished from other STAT family members by its exclusive involvement in type I and III interferon (IFN-I/III) signaling pathways, and its unique behavior as both positive and negative regulator of IFN-I signaling. The clinical relevance of these opposing STAT2 functions is exemplified by monogenic diseases of STAT2. Autosomal recessive STAT2 deficiency results in heightened susceptibility to severe and/or recurrent viral disease, whereas homozygous missense substitution of the STAT2-R148 residue is associated with severe type I interferonopathy due to loss of STAT2 negative regulation. Here we review the clinical presentation, pathogenesis, and management of these disorders of STAT2.

BRD9 is a druggable component of interferon-stimulated gene expression and antiviral activity

Interferon (IFN) induction of IFN-stimulated genes (ISGs) creates a formidable protective antiviral state. However, loss of appropriate control mechanisms can result in constitutive pathogenic ISG upregulation. Here, we used genome-scale loss-of-function screening to establish genes critical for IFN-induced transcription, identifying all expected members of the JAK-STAT signaling pathway and a previously unappreciated epigenetic reader, bromodomain-containing protein 9 (BRD9), the defining subunit of non-canonical BAF (ncBAF) chromatin-remodeling complexes. Genetic knockout or small-molecule-mediated degradation of BRD9 limits IFN-induced expression of a subset of ISGs in multiple cell types and prevents IFN from exerting full antiviral activity against several RNA and DNA viruses, including influenza virus, human immunodeficiency virus (HIV1), and herpes simplex virus (HSV1). Mechanistically, BRD9 acts at the level of transcription, and its IFN-triggered proximal association with the ISG transcriptional activator, STAT2, suggests a functional localization at selected ISG promoters. Furthermore, BRD9 relies on its intact acetyl-binding bromodomain and unique ncBAF scaffolding interaction with GLTSCR1/1L to promote IFN action. Given its druggability, BRD9 is an attractive target for dampening ISG expression under certain autoinflammatory conditions.

Type I Interferons in the Pathogenesis and Treatment of Autoimmune Diseases

Type I interferons (IFN-Is) are a very important group of cytokines that are produced by innate immune cells but also act on adaptive immune cells. IFN-Is possess antiviral, antitumor, and anti-proliferative effects, as well are associated with the initiation and maintenance of autoimmune disorders. Studies have shown that aberrantly expressed IFN-Is and/or type I IFN-inducible gene signatures in the serum or tissues of patients with autoimmune disorders are linked to their pathogenesis, clinical manifestations, and disease activity. Type I interferonopathies with mutations in genes impacting the type I IFN signaling pathway have shown symptoms and characteristics similar to those of systemic lupus erythematosus (SLE). Furthermore, both interventions in animal models and clinical trials of therapies targeting the type I IFN signaling pathway have shown efficacy in the treatment of autoimmune diseases. Our review aims to summarize the functions and targeted therapies (as well as clinical trials) of IFN-Is in both adult and pediatric autoimmune diseases, such as SLE, pediatric SLE (pSLE), rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), juvenile dermatomyositis (JDM), Sjögren syndrome (SjS), and systemic sclerosis (SSc), discussing the potential abnormal regulation of transcription factors and epigenetic modifications and providing a potential mechanism for pathogenesis and therapeutic strategies for future clinical use.

USP18 positively regulates innate antiviral immunity by promoting K63-linked polyubiquitination of MAVS

Activation of MAVS, an adaptor molecule in Rig-I-like receptor (RLR) signaling, is indispensable for antiviral immunity, yet the molecular mechanisms modulating MAVS activation are not completely understood. Ubiquitination has a central function in regulating the activity of MAVS. Here, we demonstrate that a mitochondria-localized deubiquitinase USP18 specifically interacts with MAVS, promotes K63-linked polyubiquitination and subsequent aggregation of MAVS. USP18 upregulates the expression and production of type I interferon following infection with Sendai virus (SeV) or Encephalomyocarditis virus (EMCV). Mice with a deficiency of USP18 are more susceptible to RNA virus infection. USP18 functions as a scaffold protein to facilitate the re-localization of TRIM31 and enhances the interaction between TRIM31 and MAVS in mitochondria. Our results indicate that USP18 functions as a post-translational modulator of MAVS-mediated antiviral signaling.

Ubiquitination has an important function in the regulation of antiviral immunity involving the signalling molecule MAVS. Here the authors investigate deubiquitinating enzymes and show USP18 regulates MAVS mediated antiviral signalling through modulating the ubiquitination of MAVS via promotion of interaction between MAVS and TRIM31.

Systemic Type I IFN Inflammation in Human ISG15 Deficiency Leads to Necrotizing Skin Lesions

Most monogenic disorders have a primary clinical presentation. Inherited ISG15 deficiency, however, has manifested with two distinct presentations to date: susceptibility to mycobacterial disease and intracranial calcifications from hypomorphic interferon-II (IFN-II) production and excessive IFN-I response, respectively. Accordingly, these patients were managed for their infectious and neurologic complications. Herein, we describe five new patients with six novel ISG15 mutations presenting with skin lesions who were managed for dermatologic disease. Cellularly, we denote striking specificity to the IFN-I response, which was previously assumed to be universal. In peripheral blood, myeloid cells display the most robust IFN-I signatures. In the affected skin, IFN-I signaling is observed in the keratinocytes of the epidermis, endothelia, and the monocytes and macrophages of the dermis. These findings define the specific cells causing circulating and dermatologic inflammation and expand the clinical spectrum of ISG15 deficiency to dermatologic presentations as a third phenotype co-dominant to the infectious and neurologic manifestations.

Martin-Fernandez et al. report on five patients with inherited ISG15 deficiency, a recently discovered syndrome of type I IFN autoinflammation and mycobacterial susceptibility. This study defines an expanded clinical spectrum that now includes dermatologic disease and pinpoints the specific cell types driving inflammation.