ABSTRACT Juvenile dermatomyositis (JDM) is characterized by a type I interferon (IFN-I) signature associated with disease activity. We previously identified a link between SARS-CoV-2 infection and the onset or relapse of JDM. Here, we show that newly diagnosed JDM patients display an overexpression of IFIH1 (encoding MDA5 protein) at baseline, coupled with an altered response to dsRNA stimulation at proteomic and transcriptomic levels, indicating abnormal activation of this antiviral sensing pathway. Single-cell transcriptomic and chromatin accessibility profiling of peripheral blood mononuclear cells (PBMCs) further revealed myeloid-specific enrichment of interferon-stimulated genes (ISGs) and preferential disruption of this pathway at disease onset, supporting a dysregulated IFN-I state in this cell type. We identified SARS-CoV-2 RNA in muscle biopsies of two Covid-19 pandemic-onset JDM patients, strongly implicating viral infection as a potential trigger of the dysregulated MDA5 immune response. To extend these observations beyond SARS-CoV-2, we screened two independent retrospective cohorts for antibodies against 27 common childhood infections. In our discovery cohort JDM patients showed significantly increased exposure to 4 RNA viruses in line with our immunological findings. Increased exposure to RSV B was confirmed in an independent replication cohort supporting a robust association with JDM pathophysiology. Together, these findings integrate systemic, single-cell, and tissue-level analyses implicating RNA viral infection and biased antiviral sensing in shaping IFN-I responses at JDM onset, providing mechanistic insight into environmentally triggered pathogenesis. One sentence summary Type I interferon dysregulation at juvenile dermatomyositis onset implicates altered dsRNA sensing and RNA viral exposure as potential disease triggers.

TBK1 kinase is a central regulator of type I IFN production. Upon activation of the IFN-β induction pathway, TBK1-adaptor proteins (NAP1, SINTBAD, TANK) form liquid condensates. We show that NAP1 condensates concentrate TBK1. Using NAP1KO cell lines, we demonstrate that NAP1 exerts a dual effect on TBK1 activity. Initially, NAP1 binds TBK1 and increases its activity, promoting IFN pathway activation. Subsequently, TBK1-mediated phosphorylation of NAP1 induces the formation of condensates. These NAP1 condensates concentrate both TBK1 and the phosphatase PP2A, which dephosphorylates and consequently deactivates TBK1, thus limiting IFN induction. Additionally, in patients with lupus or interferonopathies, we identify NAP1 variants unable to form condensates upon danger signal exposure, which sustain TBK1 activation without limiting its activity. This study reveals a mode of regulating a signaling pathway through condensate formation and provides a potential molecular explanation for immune dysregulation associated with NAP1 variants in certain patients with interferonopathies. TBK1 kinase is a key regulator of type I interferon production and upon activation the TBK1adaptor proteins are known to form liquid condensates. Here the authors show NAP1 is a rheostat, switching from activator to limiter of interferon via the sequestration of TBK1 within condensates.

Neurodegeneration (ND) is a severe complication of Langerhans cell histiocytosis (LCH), often leading to progressive neurological decline. We evaluated the usefulness of using plasma and cerebrospinal fluid neurofilament light chain (p- and CSF-NFL) levels as biomarkers to identify and monitor ND-LCH. NFL levels were measured using the single-molecule array for a subset of patients from the French National LCH Registry. NFL levels in 692 plasma and 115 CSF samples from 273 registry-enrolled children were analysed. Based on 84 paired plasma and CSF samples from 67 patients, p- and CSF-NFL levels were strongly correlated (p < 0.0001). The areas under the receiver operating characteristics curves for ND-LCH were 72% (95% confidence interval [CI], 64%-78%) for p-NFL and 94% (95% CI, 88%-98%) for CSF-NFL. The highest p-NFL (13.7 vs. 7.2 pg/mL; z-score 2.3 vs. 0.6) and CSF-NFL (436.9 vs. 65.2 pg/mL) levels were significantly higher for ND-LCH than in no-ND-LCH patients, respectively (p < 0.0001). Plasma NFL levels were not elevated at LCH diagnosis. At LCH diagnosis, p-NFL was not predictive of ND, but it may serve as a minimally invasive screening tool for ND in LCH, although optimal timing remains to be determined.

IKKα, encoded by CHUK, is crucial in the non-canonical NF-κB pathway and part of the IKK complex activating the canonical pathway alongside IKKβ. The absence of IKKα causes fetal encasement syndrome in humans, fatal in utero, while an impaired IKKα-NIK interaction was reported in a single patient and causes combined immunodeficiency. Here, we describe compound heterozygous variants in the kinase domain of IKKα in a female patient with hypogammaglobulinemia, recurrent lung infections, and Hay–Wells syndrome-like features. We showed that both variants were loss-of-function. Non-canonical NF-κB activation was profoundly diminished in stromal and immune cells while the canonical pathway was unexpectedly partially impaired. Reintroducing wt CHUK restored non-canonical NF-κB activation. The patient had neutralizing autoantibodies against type I IFN, akin to non-canonical NF-κB pathway deficiencies. Thus, this is the first case of biallelic CHUK mutations disrupting IKKα kinase function, broadening non-canonical NF-κB defect understanding, and suggesting IKKα’s role in canonical NF-κB target gene expression in humans.

Abstract Characterization of primary immune dysregulations and deficiency disorders caused by hyperactivating variants of the JAK/STAT pathway highlighted its crucial role in immune cell development and response. To systematically evaluate pathogenic JAK1 variants, we developed a structure-based predictive framework adapting AlphaFold2, modeling both the active and inactive conformations of JAK1. Dual-state modeling of 21,926 JAK1 variants enabled discrimination between pathogenic and benign variants based on their impact on regulatory conformation. Applying this approach to a large cohort of patients with suspected primary immune dysregulation and deficiency led to the identification of five novel variants located in key cis-regulatory and catalytic domains, with predicted gain of function activity. Ectopic expression of these variants in cell line resulted in varying levels of hyperactivation of JAK1 and multiple STATs at baseline. Furthermore, treatment of two patients with Tofacitinib suppressed JAK1 hyperactivation, normalized plasma cytokine levels and interferon signatures, and significantly improved clinical symptoms. These findings reveal diverse mechanisms of JAK1 gain of function, expanding the clinical spectrum JAK1 GOF, and underscore the importance of precise variant characterization for effective personalized therapy.

BACKGROUND:Allogenic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) are potentially curative treatments for severe combined immunodeficiency (SCID). Late-onset posttreatment manifestations (such as persistent hepatitis) are not uncommon. OBJECTIVE:We sought to characterize the prevalence and pathophysiology of persistent hepatitis in transplanted SCID patients (SCIDH+) and to evaluate risk factors and treatments. METHODS:We used various techniques (including pathology assessments, metagenomics, single-cell transcriptomics, and cytometry by time of flight) to perform an in-depth study of different tissues from patients in the SCIDH+ group and corresponding asymptomatic similarly transplanted SCID patients without hepatitis (SCIDH-). RESULTS:Eleven patients developed persistent hepatitis (median of 6 years after HSCT or GT). This condition was associated with the chronic detection of enteric viruses (human Aichi virus, norovirus, and sapovirus) in liver and/or stools, which were not found in stools from the SCIDH- group (n = 12). Multiomics analysis identified an expansion of effector memory CD8+ T cells with high type I and II interferon signatures. Hepatitis was associated with absence of myeloablation during conditioning, split chimerism, and defective B-cell function, representing 25% of the 44 patients with SCID having these characteristics. Partially myeloablative retransplantation or GT of patients with this condition (which we have named as "enteric virus infection associated with hepatitis") led to the reconstitution of T- and B-cell immunity and remission of hepatitis in 5 patients, concomitantly with viral clearance. CONCLUSIONS:Enteric virus infection associated with hepatitis is related to chronic enteric viral infection and immune dysregulation and is an important risk for transplanted SCID patients with defective B-cell function.

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regu-lation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a Rho-guanosine triphosphate hydrolases involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but, to the best of our knowledge, has never been described to date. We studied 8 male patients, from 7 unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoim-munity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifes-tations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B-lymphoblastoid cell lines from patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymeri-zation during migration. Knock down of DOCK11 recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells and primary activated T cells from healthy controls. Lastly, in line with the patients' autoim-mune manifestations, we also observed abnormal regulatory T-cell (Treg) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found reduced T-cell proliferation and impaired STAT5B phosphorylation upon interleukin-2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune -related actinopathy leading to impaired CDC42 activity and STAT5 activation, and is associated with abnormal actin cytoskeleton remodeling as well as Treg phenotype, culminating in immune dysregulation and severe early-onset autoimmunity.

SARS-CoV-2 infection in children is generally milder than in adults, yet a proportion of cases result in hyperinflammatory conditions often including myocarditis. To better understand these cases, we applied a multi-parametric approach to the study of blood cells of 56 children hospitalized with suspicion of SARS-CoV-2 infection. The most severe forms of MIS-C (multisystem inflammatory syndrome in children related to SARS-CoV-2), that resulted in myocarditis, were characterized by elevated levels of pro-angiogenesis cytokines and several chemokines. Single-cell transcriptomic analyses identified a unique monocyte/dendritic cell gene signature that correlated with the occurrence of severe myocarditis, characterized by sustained NF-κB activity, TNF-α signaling, associated with decreased gene expression of NF-κB inhibitors. We also found a weak response to type-I and type-II interferons, hyperinflammation and response to oxidative stress related to increased HIF-1α and VEGF signaling. These results provide potential for a better understanding of disease pathophysiology.

AimsWe have shown that extracellular vesicles (EVs) secreted by embryonic stem cell-derived cardiovascular progenitor cells (Pg) recapitulate the therapeutic effects of their parent cells in a mouse model of chronic heart failure (CHF). Our objectives are to investigate whether EV released by more readily available cell sources are therapeutic, whether their effectiveness is influenced by the differentiation state of the secreting cell, and through which mechanisms they act.Methods and resultsThe total EV secreted by human induced pluripotent stem cell-derived cardiovascular progenitors (iPSC-Pg) and human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) were isolated by ultracentrifugation and characterized by Nanoparticle Tracking Analysis, western blot, and cryo-electron microscopy. In vitro bioactivity assays were used to evaluate their cellular effects. Cell and EV microRNA (miRNA) content were assessed by miRNA array. Myocardial infarction was induced in 199 nude mice. Three weeks later, mice with left ventricular ejection fraction (LVEF) ≤ 45% received transcutaneous echo-guided injections of iPSC-CM (1.4 × 106, n = 19), iPSC-Pg (1.4 × 106, n = 17), total EV secreted by 1.4 × 106 iPSC-Pg (n = 19), or phosphate-buffered saline (control, n = 17) into the peri-infarct myocardium. Seven weeks later, hearts were evaluated by echocardiography, histology, and gene expression profiling, blinded to treatment group. In vitro, EV were internalized by target cells, increased cell survival, cell proliferation, and endothelial cell migration in a dose-dependent manner and stimulated tube formation. Extracellular vesicles were rich in miRNAs and most of the 16 highly abundant, evolutionarily conserved miRNAs are associated with tissue-repair pathways. In vivo, EV outperformed cell injections, significantly improving cardiac function through decreased left ventricular volumes (left ventricular end systolic volume: -11%, P < 0.001; left ventricular end diastolic volume: -4%, P = 0.002), and increased LVEF (+14%, P < 0.0001) relative to baseline values. Gene profiling revealed that EV-treated hearts were enriched for tissue reparative pathways.ConclusionExtracellular vesicles secreted by iPSC-Pg are effective in the treatment of CHF, possibly, in part, through their specific miRNA signature and the associated stimulation of distinct cardioprotective pathways. The processing and regulatory advantages of EV could make them effective substitutes for cell transplantation.

INTRODUCTION:Polymorphisms in the type III interferon IFN-λ3 and the killer cell immunoglobulin-like receptor (KIR) genes controlling the activity of natural killer (NK) cells can predict spontaneous resolution of acute hepatitis C virus (HCV) infection. We hypothesized that IFN-λ3 polymorphism may modulate NK cell function during acute HCV. METHODS:We monitored the plasma levels of type III IFNs in relation to the phenotype and the function of NK cells in a cohort of people who inject drugs (PWID) during acute HCV infection with different outcomes. RESULTS:Early acute HCV was associated with high variability in type III IFNs plasma levels and the favorable IFN-λ3 CC genotype was associated with higher viral loads. Reduced expression of Natural Killer Group Protein 2A (NKG2A) was associated with lower IFN-λ3 plasma levels and the CC genotype. IFN-γ production by NK cells was higher in individuals with the CC genotype during acute infection but this did not prevent viral persistence. IFN-λ3 plasma levels did not correlate with function of NK cells and IFN-λ3 prestimulation did not affect NK cell activation and function. CONCLUSIONS:These results suggest that IFN-λ3 polymorphism indirectly influences NK cell phenotype and function during acute HCV but other factors may act in concert to determine the outcome of the infection.

Introduction: Extracellular vesicles (EV) seem to mediate the benefits of cell therapy for ischemic heart failure (IHF) but the best cellular source of EV and their mechanism of action remain unresolved. Methods: EV secreted by human induced pluripotent stem cell-derived cardiac progenitors (CPg) were isolated by ultracentrifugation. Myocardial infarction was induced in nude mice (permanent LAD occlusion). Three weeks later, mice with LVEF ≤ 45% received transcutaneous echo-guided injections in the peri-infarct myocardium of CPg (1.4x10 6 , n=17), EV secreted by CPg (same batch) over 48 hr (n=19) or PBS (control, n=17). Six weeks later, hearts were blindly evaluated by echocardiography, histology and gene expression profiling. In parallel, in vitro bio-activity assays were developed to determine if fluorescently labelled EV were internalized in cultured rat cardiomyocytes (CM) and could affect their biology following serum deprivation. CPg and EV miRNA content was also assessed by miR arrays. Results: In contrast to CPg or PBS, EV significantly improved cardiac function, as evidenced by decreased LV volumes (LVESV: -11%, p In vitro, EV were internalized by CM, induced a dose-dependent increase in CM viability and proliferation and partially restored the stress-induced impairment of CM conduction velocity in multielectrode array experiments. Among the 101 most abundant EV-miR, 12 were highly conserved across species, of which 8 targeted pathways similarly endowed with a tissue-repair potential (cell differentiation, survival, proliferation). Conclusions: hiPS-CPg-derived EV are effective in IHF treatment, possibly, in part, through EV-mediated miR transfer fostering endogenous cardiac repair. Their benefits in terms of scale-up and regulation could make them effective substitutes for cell transplantation.