Profiling Bacteria in the Lungs of Patients with Severe Influenza Versus COVID-19 with or without Aspergillosis.

RATIONALE: The influence of the lung bacterial microbiome, including potential pathogens, in patients with influenza- or COVID-19-associated pulmonary aspergillosis (IAPA or CAPA) is yet to be explored. OBJECTIVES: To explore the composition of the lung bacterial microbiome and its association with viral and fungal infection, immunity and outcome in severe influenza versus COVID-19 with or without aspergillosis. METHODS: We performed a retrospective study in mechanically ventilated influenza and COVID-19 patients with or without invasive aspergillosis in whom bronchoalveolar lavage (BAL) for bacterial culture (with or without PCR) was obtained within two weeks after ICU admission. Additionally, 16S rRNA gene sequencing data and viral and bacterial load of BAL samples from a subset of these patients, and of patients requiring non-invasive ventilation, were analyzed. We integrated 16S rRNA gene sequencing data with existing immune parameter datasets. MEASUREMENTS AND MAIN RESULTS: Potential bacterial pathogens were detected in 20% (28/142) of influenza and 37% (104/281) of COVID-19 patients, while aspergillosis was detected in 38% (54/142) of influenza and 31% (86/281) of COVID-19 patients. A significant association between bacterial pathogens in BAL and 90-day mortality was found only in influenza patients, particularly IAPA patients. COVID-19 but not influenza patients showed increased pro-inflammatory pulmonary cytokine responses to bacterial pathogens. CONCLUSIONS: Aspergillosis is more frequently detected in lungs of severe influenza patients than bacterial pathogens. Detection of bacterial pathogens associates with worse outcome in influenza patients, particularly in those with IAPA, but not in COVID-19 patients. The immunological dynamics of tripartite viral-fungal-bacterial interactions deserve further investigation. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

OTULIN haploinsufficiency predisposes to environmentally directed inflammation.

Recently, OTULIN haploinsufficiency was linked to enhanced susceptibility to Staphylococcus aureus infections accompanied by local necrosis and systemic inflammation. The pathogenesis observed in haploinsufficient patients differs from the hyperinflammation seen in classical OTULIN-related autoinflammatory syndrome (ORAS) patients and is characterized by increased susceptibility of dermal fibroblasts to S. aureus alpha toxin-inflicted cytotoxic damage. Immunological abnormalities were not observed in OTULIN haploinsufficient patients, suggesting a non-hematopoietic basis. In this research report, we investigated an Otulin+/- mouse model after in vivo provocation with lipopolysaccharide (LPS) to explore the potential role of hematopoietic-driven inflammation in OTULIN haploinsufficiency. We observed a hyperinflammatory signature in LPS-provoked Otulin+/- mice, which was driven by CD64+ monocytes and macrophages. Bone marrow-derived macrophages (BMDMs) of Otulin+/- mice demonstrated higher proinflammatory cytokine secretion after in vitro stimulation with LPS or polyinosinic:polycytidylic acid (Poly(I:C)). Our experiments in full and mixed bone marrow chimeric mice suggest that, in contrast to humans, the observed inflammation was mainly driven by the hematopoietic compartment with cell-extrinsic effects likely contributing to inflammatory outcomes. Using an OTULIN haploinsufficient mouse model, we validated the role of OTULIN in the regulation of environmentally directed inflammation.

A Pathology-based Case Series of Influenza- and COVID-19-associated Pulmonary Aspergillosis: The Proof Is in the Tissue.

Rationale: Invasive pulmonary aspergillosis has emerged as a frequent coinfection in severe coronavirus disease (COVID-19), similarly to influenza, yet the clinical invasiveness is more debated. Objectives: We investigated the invasive nature of pulmonary aspergillosis in histology specimens of influenza and COVID-19 ICU fatalities in a tertiary care center. Methods: In this monocentric, descriptive, retrospective case series, we included adult ICU patients with PCR-proven influenza/COVID-19 respiratory failure who underwent postmortem examination and/or tracheobronchial biopsy during ICU admission from September 2009 until June 2021. Diagnosis of probable/proven viral-associated pulmonary aspergillosis (VAPA) was made based on the Intensive Care Medicine influenza-associated pulmonary aspergillosis and the European Confederation of Medical Mycology (ECMM) and the International Society for Human and Animal Mycology (ISHAM) COVID-19-associated pulmonary aspergillosis consensus criteria. All respiratory tissues were independently reviewed by two experienced pathologists. Measurements and Main Results: In the 44 patients of the autopsy-verified cohort, 6 proven influenza-associated and 6 proven COVID-19-associated pulmonary aspergillosis diagnoses were identified. Fungal disease was identified as a missed diagnosis upon autopsy in 8% of proven cases (n = 1/12), yet it was most frequently found as confirmation of a probable antemortem diagnosis (n = 11/21, 52%) despite receiving antifungal treatment. Bronchoalveolar lavage galactomannan testing showed the highest sensitivity for VAPA diagnosis. Among both viral entities, an impeded fungal growth was the predominant histologic pattern of pulmonary aspergillosis. Fungal tracheobronchitis was histologically indistinguishable in influenza (n = 3) and COVID-19 (n = 3) cases, yet macroscopically more extensive at bronchoscopy in influenza setting. Conclusions: A proven invasive pulmonary aspergillosis diagnosis was found regularly and with a similar histological pattern in influenza and in COVID-19 ICU case fatalities. Our findings highlight an important need for VAPA awareness, with an emphasis on mycological bronchoscopic work-up.

A Multimodal Imaging-Supported Down Syndrome Mouse Model of RSV Infection.

Individuals with Down syndrome (DS) are more prone to develop severe respiratory tract infections. Although a RSV infection has a high clinical impact and severe outcome in individuals with DS, no vaccine nor effective therapeutics are available. Any research into infection pathophysiology or prophylactic and therapeutic antiviral strategies in the specific context of DS would greatly benefit this patient population, but currently such relevant animal models are lacking. This study aimed to develop and characterize the first mouse model of RSV infection in a DS-specific context. Ts65Dn mice and wild type littermates were inoculated with a bioluminescence imaging-enabled recombinant human RSV to longitudinally track viral replication in host cells throughout infection progression. This resulted in an active infection in the upper airways and lungs with similar viral load in Ts65Dn mice and euploid mice. Flow cytometric analysis of leukocytes in lungs and spleen demonstrated immune alterations with lower CD8+ T cells and B-cells in Ts65Dn mice. Overall, our study presents a novel DS-specific mouse model of hRSV infection and shows that potential in using the Ts65Dn preclinical model to study immune-specific responses of RSV in the context of DS and supports the need for models representing the pathological development.

Lung epithelial and myeloid innate immunity in influenza-associated or COVID-19-associated pulmonary aspergillosis: an observational study.

BACKGROUND: Influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) affect about 15% of critically ill patients with influenza or COVID-19, respectively. These viral-fungal coinfections are difficult to diagnose and are associated with increased mortality, but data on their pathophysiology are scarce. We aimed to explore the role of lung epithelial and myeloid innate immunity in patients with IAPA or CAPA. METHODS: In this observational study, we retrospectively recruited patients who had been admitted to the intensive care unit (ICU) of University Hospitals Leuven, Belgium, requiring non-invasive or invasive ventilation because of severe influenza or COVID-19, with or without aspergillosis, between Jan 1, 2011, and March 31, 2021, whose bronchoalveolar lavage samples were available at the hospital biobank. Additionally, biobanked in vivo tracheobronchial biopsy samples from patients with IAPA or CAPA and invasive Aspergillus tracheobronchitis admitted to ICUs requiring invasive ventilation between the same dates were collected from University Hospitals Leuven, Hospital Network Antwerp (Belgium), and Amiens-Picardie University Hospital (France). We did nCounter gene expression analysis of 755 genes linked to myeloid innate immunity and protein analysis of 47 cytokines, chemokines, and growth factors on the bronchoalveolar lavage samples. Gene expression data were used to infer cell fractions by use of CIBERSORTx, to perform hypergeometric enrichment pathway analysis and gene set enrichment analysis, and to calculate pathway module scores for the IL-1ß, TNF-α, type I IFN, and type II IFN (IFNγ) pathways. We did RNAScope targeting influenza virus or SARS-CoV-2 RNA and GeoMx spatial transcriptomics on the tracheobronchial biopsy samples. FINDINGS: Biobanked bronchoalveolar lavage samples were retrieved from 166 eligible patients, of whom 40 had IAPA, 52 had influenza without aspergillosis, 33 had CAPA, and 41 had COVID-19 without aspergillosis. We did nCounter gene expression analysis on bronchoalveolar lavage samples from 134 patients, protein analysis on samples from 162 patients, and both types of analysis on samples from 130 patients. We performed RNAScope and spatial transcriptomics on the tracheobronchial biopsy samples from two patients with IAPA plus invasive Aspergillus tracheobronchitis and two patients with CAPA plus invasive Aspergillus tracheobronchitis. We observed a downregulation of genes associated with antifungal effector functions in patients with IAPA and, to a lesser extent, in patients with CAPA. We found a downregulated expression of several genes encoding proteins with functions in the opsonisation, recognition, and killing of conidia in patients with IAPA versus influenza only and in patients with CAPA versus COVID-19 only. Several genes related to LC3-associated phagocytosis, autophagy, or both were differentially expressed. Patients with CAPA had significantly lower neutrophil cell fractions than did patients with COVID-19 only. Patients with IAPA or CAPA had downregulated IFNγ signalling compared with patients with influenza only or COVID-19 only, respectively. The concentrations of several fibrosis-related growth factors were significantly elevated in the bronchoalveolar lavage fluid from patients with IAPA versus influenza only and from patients with CAPA versus COVID-19 only. In one patient with CAPA, we visualised an active or very recent SARS-CoV-2 infection disrupting the epithelial barrier, facilitating tissue-invasive aspergillosis. INTERPRETATION: Our results reveal a three-level breach in antifungal immunity in IAPA and CAPA, affecting the integrity of the epithelial barrier, the capacity to phagocytise and kill Aspergillus spores, and the ability to destroy Aspergillus hyphae, which is mainly mediated by neutrophils. The potential of adjuvant IFNγ in the treatment of IAPA and CAPA should be investigated. FUNDING: Research Foundation Flanders, Coronafonds, the Max Planck Society, the Fundação para a Ciência e a Tecnologia, the European Regional Development Fund, "la Caixa" Foundation, and Horizon 2020.

Longitudinal multimodal imaging-compatible mouse model of triazole-sensitive and -resistant invasive pulmonary aspergillosis.

Invasive pulmonary aspergillosis (IPA) caused by the mold Aspergillus fumigatus is one of the most important life-threatening infections in immunocompromised patients. The alarming increase of isolates resistant to the first-line recommended antifungal therapy urges more insights into triazole-resistant A. fumigatus infections. In this study, we systematically optimized a longitudinal multimodal imaging-compatible neutropenic mouse model of IPA. Reproducible rates of pulmonary infection were achieved through immunosuppression (sustained neutropenia) with 150 mg/kg cyclophosphamide at day -4, -1 and 2, and an orotracheal inoculation route in both sexes. Furthermore, increased sensitivity of in vivo bioluminescence imaging for fungal burden detection, as early as the day after infection, was achieved by optimizing luciferin dosing and through engineering isogenic red-shifted bioluminescent A. fumigatus strains, one wild type and two triazole-resistant mutants. We successfully tested appropriate and inappropriate antifungal treatment scenarios in vivo with our optimized multimodal imaging strategy, according to the in vitro susceptibility of our luminescent fungal strains. Therefore, we provide novel essential mouse models with sensitive imaging tools for investigating IPA development and therapy in triazole-susceptible and triazole-resistant scenarios.

Use of Micro-Computed Tomography to Visualize and Quantify COVID-19 Vaccine Efficiency in Free-Breathing Hamsters.

The SARS-CoV-2 pandemic has impacted the health of humanity after the outbreak in Hubei, China in late December 2019. Ever since, it has taken unprecedented proportions and rapidity causing over a million fatal cases. Recently, a robust Syrian golden hamster model recapitulating COVID-19 was developed in search for effective therapeutics and vaccine candidates. However, overt clinical disease symptoms were largely absent despite high levels of virus replication and associated pathology in the respiratory tract. Therefore, we used micro-computed tomography (µCT) to longitudinally visualize lung pathology and to preclinically assess candidate vaccines. µCT proved to be crucial to quantify and noninvasively monitor disease progression, to evaluate candidate vaccine efficacy, and to improve screening efforts by allowing longitudinal data without harming live animals. Here, we give a comprehensive guide on how to use low-dose high-resolution µCT to follow-up SARS-CoV-2-induced disease and test the efficacy of COVID-19 vaccine candidates in hamsters. Our approach can likewise be applied for the preclinical assessment of antiviral and anti-inflammatory drug treatments in vivo.

An affinity-enhanced, broadly neutralizing heavy chain-only antibody protects against SARS-CoV-2 infection in animal models.

Broadly neutralizing antibodies are an important treatment for individuals with coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Antibody-based therapeutics are also essential for pandemic preparedness against future Sarbecovirus outbreaks. Camelid-derived single domain antibodies (VHHs) exhibit potent antimicrobial activity and are being developed as SARS-CoV-2­neutralizing antibody-like therapeutics. Here, we identified VHHs that neutralize both SARS-CoV-1 and SARS-CoV-2, including now circulating variants. We observed that the VHHs bound to a highly conserved epitope in the receptor binding domain of the viral spike protein that is difficult to access for human antibodies. Structure-guided molecular modeling, combined with rapid yeast-based prototyping, resulted in an affinity enhanced VHH-human immunoglobulin G1 Fc fusion molecule with subnanomolar neutralizing activity. This VHH-Fc fusion protein, produced in and purified from cultured Chinese hamster ovary cells, controlled SARS-CoV-2 replication in prophylactic and therapeutic settings in mice expressing human angiotensin converting enzyme 2 and in hamsters infected with SARS-CoV-2. These data led to affinity-enhanced selection of the VHH, XVR011, a stable anti­COVID-19 biologic that is now being evaluated in the clinic.

Early oseltamivir reduces risk for influenza-associated aspergillosis in a double-hit murine model.

Invasive pulmonary aspergillosis (IPA) is a life-threatening fungal infection occurring mainly in immunocompromised patients. We recently identified IPA as an emerging co-infection with high mortality in critically ill, but otherwise immunocompetent influenza patients. The neuraminidase inhibitor oseltamivir is the current standard-of-care treatment in hospitalized influenza patients; however, its efficacy in influenza-associated pulmonary aspergillosis (IAPA) is not known. Therefore, we have established an imaging-supported double-hit mouse model to investigate the therapeutic effect of oseltamivir on the development of IAPA. Immunocompetent mice received intranasal instillation influenza A or PBS followed by orotracheal inoculation with Aspergillus fumigatus 4 days later. Oseltamivir treatment or placebo was started at day 0, day 2, or day 4. Daily monitoring included micro-computed tomography and bioluminescence imaging of pneumonia and fungal burden. Non-invasive biomarkers were complemented with imaging, molecular, immunological, and pathological analysis. Influenza virus-infected immunocompetent mice developed proven airway IPA upon co-infection with Aspergillus fumigatus, whereas non-influenza-infected mice fully cleared Aspergillus, confirming influenza as a risk factor for developing IPA. Longitudinal micro-CT showed pulmonary lesions after influenza infection worsening after Aspergillus co-infection, congruent with bioluminescence imaging and histology confirming Aspergillus pneumonia. Early oseltamivir treatment prevented severe influenza pneumonia and mitigated the development of IPA and associated mortality. A time-dependent treatment effect was consistently observed with imaging, molecular, and pathological analyses. Hence, our findings underscore the importance of initiating oseltamivir as soon as possible, to suppress influenza infection and mitigate the risk of potentially lethal IAPA disease.

Comparing infectivity and virulence of emerging SARS-CoV-2 variants in Syrian hamsters.

BACKGROUND: Within one year after its emergence, more than 108 million people acquired SARS-CoV-2 and almost 2·4 million succumbed to COVID-19. New SARS-CoV-2 variants of concern (VoC) are emerging all over the world, with the threat of being more readily transmitted, being more virulent, or escaping naturally acquired and vaccine-induced immunity. At least three major prototypic VoC have been identified, i.e. the United Kingdom, UK (B.1.1.7), South African (B.1.351) and Brazilian (B.1.1.28.1) variants. These are replacing formerly dominant strains and sparking new COVID-19 epidemics. METHODS: We studied the effect of infection with prototypic VoC from both B.1.1.7 and B.1.351 variants in female Syrian golden hamsters to assess their relative infectivity and virulence in direct comparison to two basal SARS-CoV-2 strains isolated in early 2020. FINDINGS: A very efficient infection of the lower respiratory tract of hamsters by these VoC is observed. In line with clinical evidence from patients infected with these VoC, no major differences in disease outcome were observed as compared to the original strains as was quantified by (i) histological scoring, (ii) micro-computed tomography, and (iii) analysis of the expression profiles of selected antiviral and pro-inflammatory cytokine genes. Noteworthy however, in hamsters infected with VoC B.1.1.7, a particularly strong elevation of proinflammatory cytokines was detected. INTERPRETATION: We established relevant preclinical infection models that will be pivotal to assess the efficacy of current and future vaccine(s) (candidates) as well as therapeutics (small molecules and antibodies) against two important SARS-CoV-2 VoC. FUNDING: Stated in the acknowledgment.

Lung Functioning and Inflammation in a Mouse Model of Systemic Juvenile Idiopathic Arthritis.

Systemic juvenile idiopathic arthritis (sJIA) is an immune disorder characterized by fever, skin rash, arthritis and splenomegaly. Recently, increasing number of sJIA patients were reported having lung disease. Here, we explored lung abnormalities in a mouse model for sJIA relying on injection of IFN-γ deficient (IFN-γ KO) mice with complete Freund's adjuvant (CFA). Monitoring of lung changes during development of sJIA using microcomputer tomography revealed a moderate enlargement of lungs, a decrease in aerated and increase in non-aerated lung density. When lung function and airway reactivity to methacholine was assessed, gender differences were seen. While male mice showed an increased tissue hysteresivity, female animals were characterized by an increased airway hyperactivity, mirroring ongoing inflammation. Histologically, lungs of sJIA-like mice showed subpleural and parenchymal cellular infiltrates and formation of small granulomas. Flow cytometric analysis identified immature and mature neutrophils, and activated macrophages as major cell infiltrates. Lung inflammation in sJIA-like mice was accompanied by augmented expression of IL-1ß and IL-6, two target cytokines in the treatment of sJIA. The increased expression of granulocyte colony stimulating factor, a potent inducer of granulopoiesis, in lungs of mice was striking considering the observed neutrophilia in patients. We conclude that development of sJIA in a mouse model is associated with lung inflammation which is distinct to the lung manifestations seen in sJIA patients. Our observations however underscore the importance of monitoring lung disease during systemic inflammation and the model provides a tool to explore the underlying mechanism of lung pathology in an autoinflammatory disease context.

Overcome Double Trouble: Baloxavir Marboxil Suppresses Influenza Thereby Mitigating Secondary Invasive Pulmonary Aspergillosis.

Influenza-associated pulmonary aspergillosis (IAPA) is a global recognized superinfection in critically ill influenza patients. Baloxavir marboxil, a cap-dependent endonuclease inhibitor, is a newly approved anti-influenza therapeutic. Although the benefits as a treatment for influenza are clear, its efficacy against an influenza-A. fumigatus co-infection has yet to be determined. We investigated the therapeutic effect of baloxavir marboxil in a murine model for IAPA. Immunocompetent mice received intranasal instillation of influenza A followed by orotracheal inoculation with Aspergillus fumigatus 4 days later. Administration of baloxavir marboxil or sham was started at day 0, day 2 or day 4. Mice were monitored daily for overall health status, lung pathology with micro-computed tomography (µCT) and fungal burden with bioluminescence imaging (BLI). In vivo imaging was supplemented with virological, mycological and biochemical endpoint investigations. We observed an improved body weight, survival and viral clearance in baloxavir marboxil treated mice. µCT showed less pulmonary lesions and bronchial dilation after influenza and after Aspergillus co-infection in a treatment-dependent pattern. Furthermore, baloxavir marboxil was associated with effective inhibition of fungal invasion. Hence, our results provide evidence that baloxavir marboxil mitigates severe influenza thereby decreasing the susceptibility to a lethal invasive Aspergillus superinfection.

A single-dose live-attenuated YF17D-vectored SARS-CoV-2 vaccine candidate.

The expanding pandemic of coronavirus disease 2019 (COVID-19) requires the development of safe, efficacious and fast-acting vaccines. Several vaccine platforms are being leveraged for a rapid emergency response1. Here we describe the development of a candidate vaccine (YF-S0) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that uses live-attenuated yellow fever 17D (YF17D) vaccine as a vector to express a noncleavable prefusion form of the SARS-CoV-2 spike antigen. We assess vaccine safety, immunogenicity and efficacy in several animal models. YF-S0 has an excellent safety profile and induces high levels of SARS-CoV-2 neutralizing antibodies in hamsters (Mesocricetus auratus), mice (Mus musculus) and cynomolgus macaques (Macaca fascicularis), and-concomitantly-protective immunity against yellow fever virus. Humoral immunity is complemented by a cellular immune response with favourable T helper 1 polarization, as profiled in mice. In a hamster model2 and in macaques, YF-S0 prevents infection with SARS-CoV-2. Moreover, a single dose conferred protection from lung disease in most of the vaccinated hamsters within as little as 10 days. Taken together, the quality of the immune responses triggered and the rapid kinetics by which protective immunity can be attained after a single dose warrant further development of this potent SARS-CoV-2 vaccine candidate.

STAT2 signaling restricts viral dissemination but drives severe pneumonia in SARS-CoV-2 infected hamsters.

Emergence of SARS-CoV-2 causing COVID-19 has resulted in hundreds of thousands of deaths. In search for key targets of effective therapeutics, robust animal models mimicking COVID-19 in humans are urgently needed. Here, we show that Syrian hamsters, in contrast to mice, are highly permissive to SARS-CoV-2 and develop bronchopneumonia and strong inflammatory responses in the lungs with neutrophil infiltration and edema, further confirmed as consolidations visualized by micro-CT alike in clinical practice. Moreover, we identify an exuberant innate immune response as key player in pathogenesis, in which STAT2 signaling plays a dual role, driving severe lung injury on the one hand, yet restricting systemic virus dissemination on the other. Our results reveal the importance of STAT2-dependent interferon responses in the pathogenesis and virus control during SARS-CoV-2 infection and may help rationalizing new strategies for the treatment of COVID-19 patients.

Favipiravir at high doses has potent antiviral activity in SARS-CoV-2-infected hamsters, whereas hydroxychloroquine lacks activity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly spread around the globe after its emergence in Wuhan in December 2019. With no specific therapeutic and prophylactic options available, the virus has infected millions of people of which more than half a million succumbed to the viral disease, COVID-19. The urgent need for an effective treatment together with a lack of small animal infection models has led to clinical trials using repurposed drugs without preclinical evidence of their in vivo efficacy. We established an infection model in Syrian hamsters to evaluate the efficacy of small molecules on both infection and transmission. Treatment of SARS-CoV-2-infected hamsters with a low dose of favipiravir or hydroxychloroquine with(out) azithromycin resulted in, respectively, a mild or no reduction in virus levels. However, high doses of favipiravir significantly reduced infectious virus titers in the lungs and markedly improved lung histopathology. Moreover, a high dose of favipiravir decreased virus transmission by direct contact, whereas hydroxychloroquine failed as prophylaxis. Pharmacokinetic modeling of hydroxychloroquine suggested that the total lung exposure to the drug did not cause the failure. Our data on hydroxychloroquine (together with previous reports in macaques and ferrets) thus provide no scientific basis for the use of this drug in COVID-19 patients. In contrast, the results with favipiravir demonstrate that an antiviral drug at nontoxic doses exhibits a marked protective effect against SARS-CoV-2 in a small animal model. Clinical studies are required to assess whether a similar antiviral effect is achievable in humans without toxic effects.

Defective Sec61α1 underlies a novel cause of autosomal dominant severe congenital neutropenia.

BACKGROUND: The molecular cause of severe congenital neutropenia (SCN) is unknown in 30% to 50% of patients. SEC61A1 encodes the α-subunit of the Sec61 complex, which governs endoplasmic reticulum protein transport and passive calcium leakage. Recently, mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency and glomerulocystic kidney disease. OBJECTIVE: Our aim was to expand the spectrum of SEC61A1-mediated disease to include autosomal dominant SCN. METHODS: Whole exome sequencing findings were validated, and reported mutations were compared by Western blotting, Ca2+ flux assays, differentiation of transduced HL-60 cells, in vitro differentiation of primary CD34 cells, quantitative PCR for unfolded protein response (UPR) genes, and single-cell RNA sequencing on whole bone marrow. RESULTS: We identified a novel de novo missense mutation in SEC61A1 (c.A275G;p.Q92R) in a patient with SCN who was born to nonconsanguineous Belgian parents. The mutation results in diminished protein expression, disturbed protein translocation, and an increase in calcium leakage from the endoplasmic reticulum. In vitro differentiation of CD34+ cells recapitulated the patient's clinical arrest in granulopoiesis. The impact of Q92R-Sec61α1 on neutrophil maturation was validated by using HL-60 cells, in which transduction reduced differentiation into CD11b+CD16+ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response, with single-cell analysis of primary bone marrow revealing perturbed UPR in myeloid precursors and in vitro differentiation of primary CD34+ cells revealing upregulation of CCAAT/enhancer-binding protein homologous protein and immunoglobulin heavy chain binding protein UPR-response genes. CONCLUSION: Specific mutations in SEC61A1 cause SCN through dysregulation of the UPR.