Identification of an IL-1 receptor mutation driving autoinflammation directs IL-1-targeted drug design.

The interleukin 1 (IL-1) pathway signals through IL-1 receptor type 1 (IL-1R1) and emerges as a central mediator for systemic inflammation. Aberrant IL-1 signaling leads to a range of autoinflammatory diseases. Here, we identified a de novo missense variant in IL-1R1 (p.Lys131Glu) in a patient with chronic recurrent multifocal osteomyelitis (CRMO). Patient PBMCs showed strong inflammatory signatures, particularly in monocytes and neutrophils. The p.Lys131Glu substitution affected a critical positively charged amino acid, which disrupted the binding of the antagonist ligand, IL-1Ra, but not IL-1α or IL-1ß. This resulted in unopposed IL-1 signaling. Mice with a homologous mutation exhibited similar hyperinflammation and greater susceptibility to collagen antibody-induced arthritis, accompanied with pathological osteoclastogenesis. Leveraging the biology of the mutation, we designed an IL-1 therapeutic, which traps IL-1ß and IL-1α, but not IL-1Ra. Collectively, this work provides molecular insights and a potential drug for improved potency and specificity in treating IL-1-driven diseases.

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.

A dominant autoinflammatory disease caused by non-cleavable variants of RIPK1.

Activation of RIPK1 controls TNF-mediated apoptosis, necroptosis and inflammatory pathways1. Cleavage of human and mouse RIPK1 after residues D324 and D325, respectively, by caspase-8 separates the RIPK1 kinase domain from the intermediate and death domains. The D325A mutation in mouse RIPK1 leads to embryonic lethality during mouse development2,3. However, the functional importance of blocking caspase-8-mediated cleavage of RIPK1 on RIPK1 activation in humans is unknown. Here we identify two families with variants in RIPK1 (D324V and D324H) that lead to distinct symptoms of recurrent fevers and lymphadenopathy in an autosomal-dominant manner. Impaired cleavage of RIPK1 D324 variants by caspase-8 sensitized patients' peripheral blood mononuclear cells to RIPK1 activation, apoptosis and necroptosis induced by TNF. The patients showed strong RIPK1-dependent activation of inflammatory signalling pathways and overproduction of inflammatory cytokines and chemokines compared with unaffected controls. Furthermore, we show that expression of the RIPK1 mutants D325V or D325H in mouse embryonic fibroblasts confers not only increased sensitivity to RIPK1 activation-mediated apoptosis and necroptosis, but also induction of pro-inflammatory cytokines such as IL-6 and TNF. By contrast, patient-derived fibroblasts showed reduced expression of RIPK1 and downregulated production of reactive oxygen species, resulting in resistance to necroptosis and ferroptosis. Together, these data suggest that human non-cleavable RIPK1 variants promote activation of RIPK1, and lead to an autoinflammatory disease characterized by hypersensitivity to apoptosis and necroptosis and increased inflammatory response in peripheral blood mononuclear cells, as well as a compensatory mechanism to protect against several pro-death stimuli in fibroblasts.

The Multifaceted Immunology of Cytokine Storm Syndrome.

Cytokine storm syndromes (CSSs) are potentially fatal hyperinflammatory states that share the underpinnings of persistent immune cell activation and uninhibited cytokine production. CSSs can be genetically determined by inborn errors of immunity (i.e., familial hemophagocytic lymphohistiocytosis) or develop as a complication of infections, chronic inflammatory diseases (e.g., Still disease), or malignancies (e.g., T cell lymphoma). Therapeutic interventions that activate the immune system such as chimeric Ag receptor T cell therapy and immune checkpoint inhibition can also trigger CSSs in the setting of cancer treatment. In this review, the biology of different types of CSSs is explored, and the current knowledge on the involvement of immune pathways and the contribution of host genetics is discussed. The use of animal models to study CSSs is reviewed, and their relevance for human diseases is discussed. Lastly, treatment approaches for CSSs are discussed with a focus on interventions that target immune cells and cytokines.

IL-4Rα signaling promotes barrier-altering oncostatin M and IL-6 production in aspirin-exacerbated respiratory disease.

BACKGROUND: Aspirin-exacerbated respiratory disease (AERD) is a severe disease involving dysregulated type 2 inflammation. However, the role other inflammatory pathways play in AERD is poorly understood. OBJECTIVE: We sought to broadly define the inflammatory milieu of the upper respiratory tract in AERD and to determine the effects of IL-4Rα inhibition on mediators of nasal inflammation. METHODS: Twenty-two AERD patients treated with dupilumab for 3 months were followed over 3 visits and compared to 10 healthy controls. Nasal fluid was assessed for 45 cytokines and chemokines using Olink Target 48. Blood neutrophils and cultured human mast cells, monocytes/macrophages, and nasal fibroblasts were assessed for response to IL-4/13 stimulation in vitro. RESULTS: Of the nasal fluid cytokines measured, nearly one third were higher in AERD patients compared to healthy controls, including IL-6 and the IL-6 family-related cytokine oncostatin M (OSM), both of which correlated with nasal albumin levels, a marker of epithelial barrier dysregulation. Dupilumab significantly decreased many nasal mediators, including OSM and IL-6. IL-4 stimulation induced OSM production from mast cells and macrophages but not from neutrophils, and OSM and IL-13 stimulation induced IL-6 production from nasal fibroblasts. CONCLUSION: In addition to type 2 inflammation, innate and IL-6-related cytokines are also elevated in the respiratory tract in AERD. Both OSM and IL-6 are locally produced in nasal polyps and likely promote pathology by negatively affecting epithelial barrier function. IL-4Rα blockade, although seemingly directed at type 2 inflammation, also decreases mediators of innate inflammation and epithelial dysregulation, which may contribute to dupilumab's therapeutic efficacy in AERD.

Biologics and JAK inhibitors for the treatment of monogenic systemic autoinflammatory diseases in children.

Systemic autoinflammatory diseases (SAIDs) are caused by aberrant activation of 1 or more inflammatory pathways in an antigen-independent manner. Monogenic forms of SAIDs typically manifest during childhood, and early treatment is essential to minimize morbidity and mortality. On the basis of the mechanism of disease and the dominant cytokine(s) that propagates inflammation, monogenic SAIDs can be grouped into major categories including inflammasomopathies/disorders of IL-1, interferonopathies, and disorders of nuclear factor-κB and/or aberrant TNF activity. This classification scheme has direct therapeutic relevance given the availability of biologic agents and small-molecule inhibitors that specifically target these pathways. Here, we review the experience of using biologics that target IL-1 and TNF as well as using Janus kinase inhibitors for the treatment of monogenic SAIDs in pediatric patients. We provide an evidence-based guide for the use of these medications and discuss their mechanism of action, safety profile, and strategies for therapeutic monitoring.

A gain-of-function variation in PLCG1 causes a new immune dysregulation disease.

BACKGROUND: Phospholipase C (PLC) γ1 is a critical enzyme regulating nuclear factor-κB (NF-κB), extracellular signal-related kinase, mitogen-activated protein kinase, and nuclear factor of activated T cells signaling pathways, yet germline PLCG1 mutation in human disease has not been reported. OBJECTIVE: We aimed to investigate the molecular pathogenesis of a PLCG1 activating variant in a patient with immune dysregulation. METHODS: Whole exome sequencing was used to identify the patient's pathogenic variants. Bulk RNA sequencing, single-cell RNA sequencing, quantitative PCR, cytometry by time of flight, immunoblotting, flow cytometry, luciferase assay, IP-One ELISA, calcium flux assay, and cytokine measurements in patient PBMCs and T cells and COS-7 and Jurkat cell lines were used to define inflammatory signatures and assess the impact of the PLCG1 variant on protein function and immune signaling. RESULTS: We identified a novel and de novo heterozygous PLCG1 variant, p.S1021F, in a patient presenting with early-onset immune dysregulation disease. We demonstrated that the S1021F variant is a gain-of-function variant, leading to increased inositol-1,4,5-trisphosphate production, intracellular Ca2+ release, and increased phosphorylation of extracellular signal-related kinase, p65, and p38. The transcriptome and protein expression at the single-cell level revealed exacerbated inflammatory responses in the patient's T cells and monocytes. The PLCG1 activating variant resulted in enhanced NF-κB and type II interferon pathways in T cells, and hyperactivated NF-κB and type I interferon pathways in monocytes. Treatment with either PLCγ1 inhibitor or Janus kinase inhibitor reversed the upregulated gene expression profile in vitro. CONCLUSIONS: Our study highlights the critical role of PLCγ1 in maintaining immune homeostasis. We illustrate immune dysregulation as a consequence of PLCγ1 activation and provide insight into therapeutic targeting of PLCγ1.

Comparison of disease phenotypes and mechanistic insight on causal variants in patients with DADA2.

BACKGROUND: Deficiency of adenosine deaminase 2 (DADA2) results in heterogeneous manifestations including systemic vasculitis and red cell aplasia. The basis of different disease phenotypes remains incompletely defined. OBJECTIVE: We sought to further delineate disease phenotypes in DADA2 and define the mechanistic basis of ADA2 variants. METHODS: We analyzed the clinical features and ADA2 variants in 33 patients with DADA2. We compared the transcriptomic profile of 14 patients by bulk RNA sequencing. ADA2 variants were expressed experimentally to determine impact on protein production, trafficking, release, and enzymatic function. RESULTS: Transcriptomic analysis of PBMCs from DADA2 patients with the vasculitis phenotype or pure red cell aplasia phenotype exhibited similar upregulation of TNF, type I interferon, and type II interferon signaling pathways compared with healthy controls. These pathways were also activated in 3 asymptomatic individuals with DADA2. Analysis of ADA2 variants, including 7 novel variants, showed different mechanisms of functional disruption including (1) unstable transcript leading to RNA degradation; (2) impairment of ADA2 secretion because of retention in the endoplasmic reticulum; (3) normal expression and secretion of ADA2 that lacks enzymatic function; and (4) disruption of the N-terminal signal peptide leading to cytoplasmic localization of unglycosylated protein. CONCLUSIONS: Transcriptomic signatures of inflammation are observed in patients with different disease phenotypes, including some asymptomatic individuals. Disease-associated ADA2 variants affect protein function by multiple mechanisms, which may contribute to the clinical heterogeneity of DADA2.

A Cohort Study on Deficiency of ADA2 from China.

PURPOSE: Deficiency of adenosine deaminase 2 (DADA2), an autosomal recessive autoinflammatory disorder caused by biallelic loss-of-function variants in adenosine deaminase 2 (ADA2), has not been systemically investigated in Chinese population yet. We aim to further characterize DADA2 cases in China. METHODS: A retrospective analysis of patients with DADA2 identified through whole exome sequencing (WES) at seventeen rheumatology centers across China was conducted. Clinical characteristics, laboratory findings, genotype, and treatment response were analyzed. RESULTS: Thirty patients with DADA2 were enrolled between January 2015 and December 2021. Adenosine deaminase 2 enzymatic activity was low in all tested cases to confirm pathogenicity. Median age of disease presentation was 4.3 years and the median age at diagnosis was 7.8 years. All but one patient presented during childhood and two subjects died from complications of their disease. The patients most commonly presented with systemic inflammation (92.9%), vasculitis (86.7%), and hypogammaglobinemia (73.3%) while one patient presented with bone marrow failure (BMF) with variable cytopenia. Twenty-three (76.7%) patients were treated with TNF inhibitors (TNFi), while two (6.7%) underwent hematopoietic stem cell transplantation (HSCT). They all achieved clinical remission. A total of thirty-nine ADA2 causative variants were identified, six of which were novel. CONCLUSION: To establish early diagnosis and improve clinical outcomes, genetic screening and/or testing of ADA2 enzymatic activity should be performed in patients with suspected clinical features. TNFi is considered as first line treatment for those with vascular phenotypes. HSCT may be beneficial for those with hematological disease or in those who are refractory to TNFi.

In cis "benign" SOCS1 variants linked to enhanced interferon signaling and autoimmunity.

We aimed to characterize the genetic basis of disease in a family with multiple autoimmune manifestations, including systemic lupus erythematosus (SLE), immune thrombocytopenia, and autoimmune thyroiditis. Whole exome sequencing (WES) was conducted to identify candidate variants, which were analyzed by flow cytometry, immunoblotting, immunoprecipitation, and luciferase reporter assay in transfected 293T cells. Gene expression in peripheral blood mononuclear cells (PBMC) was profiled by bulk RNA sequencing and plasma cytokines were measured by proximity extension assay. In two siblings with early-onset SLE and immune thrombocytopenia, WES identified two maternally inherited in cis variants (p. Pro50Leu and p.Ala76Gly) in Suppressor of cytokine signaling 1 (SOCS1), flanking the kinase inhibitory domain that interacts with Janus kinases (JAK). Both variants were predicted to be benign by most in silico algorithms and neither alone affected the ability of SOCS1 to inhibit JAK-STAT1 signaling by functional studies. When both variants were expressed in cis, the mutant SOCS1 protein displayed decreased binding to JAK1 and reduced capacity to inhibit type I interferon (IFN-I) signaling by ∼20-30% compared to the wildtype protein. PBMC from the probands and their mother showed increased expression of interferon-inducible genes compared to healthy controls, supporting defective regulation of IFN-I signaling. Cells from all three subjects displayed heightened sensitivity to IFN-I stimulation, while response to IFN-γ, IL-4, and IL-6 was comparable to healthy controls. Our work illustrates the critical fine-tuning of IFN-I signaling by SOCS1 to prevent autoimmunity. We show that a combination of genetic variants that are individually benign may have deleterious consequences.

Comprehensive analysis of ADA2 genetic variants and estimation of carrier frequency driven by a function-based approach.

BACKGROUND: Deficiency of adenosine deaminase 2 (DADA2) is an autoinflammatory disease caused by deleterious ADA2 variants. The frequency of these variants in the general population, and hence the expected disease prevalence, remain unknown. OBJECTIVE: We aimed to characterize the functional impact and carrier frequency of ADA2 variants. METHODS: We performed functional studies and in silico analysis on 163 ADA2 variants, including DADA2-associated variants and population variants identified in the Genome Aggregation Database. We estimated the carrier rate using the aggregate frequency of deleterious variants. RESULTS: Functional studies of ADA2 variants revealed that 77 (91%) of 85 of DADA2-associated variants reduced ADA2 enzymatic function by >75%. Analysis of 100 ADA2 variants in the database showed a full spectrum of impact on ADA2 function, rather than a dichotomy of benign versus deleterious variants. We found several in silico algorithms that effectively predicted the impact of ADA2 variants with high sensitivity and specificity, and confirmed a correlation between the residual function of ADA2 variants in vitro and the plasma ADA2 activity of individuals carrying these variants (n = 45; r = 0.649; P < .0001). Using <25% residual enzymatic activity as the cutoff to define potential pathogenicity, integration of our results with the database population data revealed an estimated carrier frequency of at least 1 in 236 individuals, corresponding to an expected DADA2 disease prevalence of ~1 in 222,000 individuals. CONCLUSIONS: Functional annotation guides the interpretation of ADA2 variants to create a framework that enables estimation of DADA2 carrier frequency and disease prevalence.

TNF inhibition in vasculitis management in adenosine deaminase 2 deficiency (DADA2).

BACKGROUND: Deficiency of adenosine deaminase 2 (DADA2) is a recessively inherited autoinflammatory disorder caused by a loss of functional ADA2 protein. TNF inhibition (TNFi) has proven to be highly effective in treating inflammatory manifestations. OBJECTIVE: We sought to explore the pathophysiology and the underlying mechanisms of TNF-inhibitor response in these patients. METHODS: We performed Sanger sequencing of the ADA2 gene. We used flow cytometry, intracellular cytokine staining, transcriptome analysis, immunohistochemistry, and cell differentiation experiments to define an inflammatory signature in patients with DADA2 and studied their response to TNF-inhibitor treatment. RESULTS: We demonstrated increased inflammatory signals and overproduction of cytokines mediated by IFN and nuclear factor kappa B pathways in patients' primary cells. Treatment with TNFi led to reduction in inflammation, rescued the skewed differentiation toward the proinflammatory M1 macrophage subset, and restored integrity of endothelial cells in blood vessels. We also report 8 novel disease-associated variants in 7 patients with DADA2. CONCLUSIONS: Our data explore the cellular mechanism underlying effective treatment with TNFi therapies in DADA2. DADA2 vasculitis is strongly related to the presence of activated myeloid cells, and the endothelial cell damage is rescued with anti-TNF treatment.

SOCS1 Haploinsufficiency Presenting as Severe Enthesitis, Bone Marrow Hypocellularity, and Refractory Thrombocytopenia in a Pediatric Patient with Subsequent Response to JAK Inhibition.

Haploinsufficiency of suppressor of cytokine signaling 1 (SOCS1) is a recently discovered autoinflammatory disorder with significant rheumatologic, immunologic, and hematologic manifestations. Here we report a case of SOCS1 haploinsufficiency in a 5-year-old child with profound arthralgias and immune-mediated thrombocytopenia unmasked by SARS-CoV-2 infection. Her clinical manifestations were accompanied by excessive B cell activity, eosinophilia, and elevated IgE levels. Uniquely, this is the first report of SOCS1 haploinsufficiency in the setting of a chromosomal deletion resulting in complete loss of a single SOCS1 gene with additional clinical findings of bone marrow hypocellularity and radiologic evidence of severe enthesitis. Immunologic profiling showed a prominent interferon signature in the patient's peripheral blood mononuclear cells, which were also hypersensitive to stimulation by type I and type II interferons. The patient showed excellent clinical and functional laboratory response to tofacitinib, a Janus kinase inhibitor that disrupts interferon signaling. Our case highlights the need to utilize a multidisciplinary diagnostic approach and consider a comprehensive genetic evaluation for inborn errors of immunity in patients with an atypical immune-mediated thrombocytopenia phenotype.

Low-ratio somatic NLRC4 mutation causes late-onset autoinflammatory disease.

OBJECTIVES: We aim to investigate the genetic basis of a case of late-onset autoinflammatory disease characterised by arthritis, recurrent fever and skin rashes. METHODS: We performed whole-exome/genome sequencing and digital droplet PCR (ddPCR) to identify the pathogenic somatic mutation. We used single-cell RNA sequencing (scRNA-seq), intracellular cytokine staining, quantitative PCR, immunohistochemistry and western blotting to define inflammatory signatures and to explore the pathogenic mechanism. RESULTS: We identified a somatic mutation in NLRC4 (p.His443Gln) with the highest mosaicism ratio in the patient's monocytes (5.69%). The somatic mutation resulted in constitutive NLRC4 activation, spontaneous apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC) aggregation, caspase-1 hyperactivation and increased production of interleukin (IL)-1ß and IL-18. Moreover, we demonstrated effective suppression of inflammatory cytokine production by targeting gasdermin D, an approach that could be considered as a novel treatment strategy for patients with NLRC4-associated autoinflammatory syndrome. CONCLUSIONS: We reported a case of a late-onset autoinflammatory disease caused by a somatic NLRC4 mutation in a small subset of leucocytes. We systemically analysed this condition at a single-cell transcriptomic level and revealed specific enhancement of inflammatory response in myeloid cells.

Coagulation profiles and viscoelastic testing in multisystem inflammatory syndrome in children.

OBJECTIVE: To characterize viscoelastic testing profiles of children with multisystem inflammatory syndrome in children (MIS-C). METHODS: This single-center retrospective review included 30 patients diagnosed with MIS-C from March 1 to September 1, 2020. Thromboelastography (TEG) with platelet mapping was performed in 19 (63%) patients and compared to age- and sex-matched controls prior to cardiac surgery. Relationships between TEG parameters and inflammatory markers were assessed using correlation. RESULTS: Patients with MIS-C had abnormal TEG results compared to controls, including decreased kinetic (K) time (1.1 vs. 1.7 minutes, p < .01), increased alpha angle (75.0° vs. 65.7°, p < .01), increased maximum amplitude (70.8 vs. 58.3 mm, p < .01), and decreased lysis in 30 minutes (Ly30) (1.1% vs. 3.7%, p = .03); consistent with increased clot formation rate and strength, and reduced fibrinolysis. TEG maximum amplitude was moderately correlated with erythrocyte sedimentation rate (ESR) (r = 0.60, p = .02), initial platelet count (r = 0.67, p < .01), and peak platelet count (r = 0.51, p = .03). TEG alpha angle was moderately correlated with peak platelet count (r = 0.54, p = .02). Seventeen (57%) patients received aspirin (ASA) and anticoagulation, five (17%) received only ASA, and three (10%) received only anticoagulation. No patients had a symptomatic thrombotic event. Six (20%) patients had a bleeding event, none of which was major. CONCLUSIONS: Patients with MIS-C had evidence of hypercoagulability on TEG. Increased ESR and platelets were associated with higher clot strength. Patients were prophylactically treated with ASA or anticoagulation with no symptomatic thrombosis or major bleeding. Further multicenter study is required to characterize the rate of thrombosis and optimal thromboprophylaxis algorithm in this patient population.

Monogenic autoinflammatory disorders: Conceptual overview, phenotype, and clinical approach.

Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.

Immune dysregulation and multisystem inflammatory syndrome in children (MIS-C) in individuals with haploinsufficiency of SOCS1.

BACKGROUND: We studied 2 unrelated patients with immune thrombocytopenia and autoimmune hemolytic anemia in the setting of acute infections. One patient developed multisystem inflammatory syndrome in children in the setting of a severe acute respiratory syndrome coronavirus 2 infection. OBJECTIVES: We sought to identify the mechanisms underlying the development of infection-driven autoimmune cytopenias. METHODS: Whole-exome sequencing was performed on both patients, and the impact of the identified variants was validated by functional assays using the patients' PBMCs. RESULTS: Each patient was found to have a unique heterozygous truncation variant in suppressor of cytokine signaling 1 (SOCS1). SOCS1 is an essential negative regulator of type I and type II IFN signaling. The patients' PBMCs showed increased levels of signal transducer and activator of transcription 1 phosphorylation and a transcriptional signature characterized by increased expression of type I and type II IFN-stimulated genes and proapoptotic genes. The enhanced IFN signature exhibited by the patients' unstimulated PBMCs parallels the hyperinflammatory state associated with multisystem inflammatory syndrome in children, suggesting the contributions of SOCS1 in regulating the inflammatory response characteristic of multisystem inflammatory syndrome in children. CONCLUSIONS: Heterozygous loss-of-function SOCS1 mutations are associated with enhanced IFN signaling and increased immune cell activation, thereby predisposing to infection-associated autoimmune cytopenias.

Genotype and functional correlates of disease phenotype in deficiency of adenosine deaminase 2 (DADA2).

BACKGROUND: Deficiency of adenosine deaminase 2 (DADA2) is a syndrome with pleiotropic manifestations including vasculitis and hematologic compromise. A systematic definition of the relationship between adenosine deaminase 2 (ADA2) mutations and clinical phenotype remains unavailable. OBJECTIVE: We sought to test whether the impact of ADA2 mutations on enzyme function correlates with clinical presentation. METHODS: Patients with DADA2 with severe hematologic manifestations were compared with vasculitis-predominant patients. Enzymatic activity was assessed using expression constructs reflecting all 53 missense, nonsense, insertion, and deletion genotypes from 152 patients across the DADA2 spectrum. RESULTS: We identified patients with DADA2 presenting with pure red cell aplasia (n = 5) or bone marrow failure (BMF, n = 10) syndrome. Most patients did not exhibit features of vasculitis. Recurrent infection, hepatosplenomegaly, and gingivitis were common in patients with BMF, of whom half died from infection. Unlike patients with DADA2 with vasculitis, patients with pure red cell aplasia and BMF proved largely refractory to TNF inhibitors. ADA2 variants associated with vasculitis predominantly reflected missense mutations with at least 3% residual enzymatic activity. In contrast, pure red cell aplasia and BMF were associated with missense mutations with minimal residual enzyme activity, nonsense variants, and insertions/deletions resulting in complete loss of function. CONCLUSIONS: Functional interrogation of ADA2 mutations reveals an association of subtotal function loss with vasculitis, typically responsive to TNF blockade, whereas more extensive loss is observed in hematologic disease, which may be refractory to treatment. These findings establish a genotype-phenotype spectrum in DADA2.

Polyarteritis nodosa and deficiency of adenosine deaminase 2 - Shared genealogy, generations apart.

Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis that predominantly affects medium-sized arteries. With the establishment and refinement of vasculitis nomenclature and diagnostic criteria, clinical findings of PAN and distinguishing features from other vasculitides are now well characterized. Although PAN typically manifests in adulthood, cohort studies in paediatric patients have shaped our understanding of childhood-onset PAN. The paradigm of childhood-onset PAN changed considerably with the landmark discovery of deficiency of ADA2 (DADA2), a monogenic cause of vasculitis that is often indistinguishable from PAN. Testing for DADA2 has provided an explanation to numerous challenging cases of familial PAN and early-onset PAN around the world. The ability to distinguish DADA2 from classic PAN have important therapeutic implications as tumor necrosis factor inhibitors have demonstrated remarkable efficacy in the treatment of DADA2. In this review, we will discuss our current understanding of PAN and DADA2 and highlight similarities and differences between these vasculitides.

Adenosine deaminase 2 as a biomarker of macrophage activation syndrome in systemic juvenile idiopathic arthritis.

OBJECTIVE: Macrophage activation syndrome (MAS) is a life-threatening complication of systemic juvenile idiopathic arthritis (sJIA) characterised by a vicious cycle of immune amplification that can culminate in overwhelming inflammation and multiorgan failure. The clinical features of MAS overlap with those of active sJIA, complicating early diagnosis and treatment. We evaluated adenosine deaminase 2 (ADA2), a protein of unknown function released principally by monocytes and macrophages, as a novel biomarker of MAS. METHODS: We established age-based normal ranges of peripheral blood ADA2 activity in 324 healthy children and adults. We compared these ranges with 173 children with inflammatory and immune-mediated diseases, including systemic and non-systemic JIA, Kawasaki disease, paediatric systemic lupus erythematosus and juvenile dermatomyositis. RESULTS: ADA2 elevation beyond the upper limit of normal in children was largely restricted to sJIA with concomitant MAS, a finding confirmed in a validation cohort of sJIA patients with inactive disease, active sJIA without MAS or sJIA with MAS. ADA2 activity strongly correlated with MAS biomarkers including ferritin, interleukin (IL)-18 and the interferon (IFN)-γ-inducible chemokine CXCL9 but displayed minimal association with the inflammatory markers C reactive protein and erythrocyte sedimentation rate. Correspondingly, ADA2 paralleled disease activity based on serial measurements in patients with recurrent MAS episodes. IL-18 and IFN-γ elicited ADA2 production by peripheral blood mononuclear cells, and ADA2 was abundant in MAS haemophagocytes. CONCLUSIONS: These findings collectively identify the utility of plasma ADA2 activity as a biomarker of MAS and lend further support to a pivotal role of macrophage activation in this condition.