Monogenic autoimmunity.

Monogenic autoimmune syndromes provide a rare yet powerful glimpse into the fundamental mechanisms of immunologic tolerance. Such syndromes reveal not only the contribution of an individual breakpoint in tolerance but also patterns in the pathogenesis of autoimmunity. Disturbances in innate immunity, a system built for ubiquitous sensing of danger signals, tend to generate systemic autoimmunity. For example, defects in the clearance of self-antigens and chronic stimulation of type 1 interferons lead to the systemic autoimmunity seen in C1q deficiency, SPENCDI, and AGS. In contrast, disturbances of adaptive immunity, which is built for antigen specificity, tend to produce organ-specific autoimmunity. Thus, the loss of lymphocyte homeostasis, whether through defects in apoptosis, suppression, or negative selection, leads to organ-specific autoimmunity in ALPS, IPEX, and APS1. We discuss the unique mechanisms of disease in these prominent syndromes as well as how they contribute to the spectrum of organ-specific or systemic autoimmunity. The continued study of rare variants in autoimmune disease will inform future investigations and treatments directed at rare and common autoimmune diseases alike.

Glucagon receptor antagonist volagidemab in type 1 diabetes: a 12-week, randomized, double-blind, phase 2 trial.

Hyperglucagonemia contributes to hyperglycemia in patients with type 1 diabetes (T1D); however, novel therapeutics that block glucagon action could improve glycemic control. This phase 2 study evaluated the safety and efficacy of volagidemab, an antagonistic monoclonal glucagon receptor (GCGR) antibody, as an adjunct to insulin therapy in adults with T1D. The primary endpoint was change in daily insulin use at week 12. Secondary endpoints included changes in hemoglobin A1c (HbA1c) at week 13, in average daily blood glucose concentration and time within target range as assessed by continuous blood glucose monitoring (CGM) and seven-point glucose profile at week 12, incidence of hypoglycemic events, the proportion of subjects who achieve HbA1c reduction of ≥0.4%, volagidemab drug concentrations and incidence of anti-drug antibodies. Eligible participants (n = 79) were randomized to receive weekly subcutaneous injections of placebo, 35 mg volagidemab or 70 mg volagidemab. Volagidemab produced a reduction in total daily insulin use at week 12 (35 mg volagidemab: -7.59 units (U) (95% confidence interval (CI) -11.79, -3.39; P = 0.040 versus placebo); 70 mg volagidemab: -6.64 U (95% CI -10.99, -2.29; P = 0.084 versus placebo); placebo: -1.27 U (95% CI -5.4, 2.9)) without meeting the prespecified significance level (P < 0.025). At week 13, the placebo-corrected reduction in HbA1c percentage was -0.53 (95% CI -0.89 to -0.17, nominal P = 0.004) in the 35 mg volagidemab group and -0.49 (95% CI -0.85 to -0.12, nominal P = 0.010) in the 70 mg volagidemab group. No increase in hypoglycemia was observed with volagidemab therapy; however, increases in serum transaminases, low-density lipoprotein (LDL)-cholesterol and blood pressure were observed. Although the primary endpoint did not meet the prespecified significance level, we believe that the observed reduction in HbA1c and tolerable safety profile provide a rationale for further randomized studies to define the long-term efficacy and safety of volagidemab in patients with T1D.

Elastase 3B mutation links to familial pancreatitis with diabetes and pancreatic adenocarcinoma.

While improvements in genetic analysis have greatly enhanced our understanding of the mechanisms behind pancreatitis, it continues to afflict many families for whom the hereditary factors remain unknown. Recent evaluation of a patient with a strong family history of pancreatitis sparked us to reexamine a large kindred originally reported over 50 years ago with an autosomal dominant inheritance pattern of chronic pancreatitis, diabetes and pancreatic adenocarcinoma. Whole exome sequencing analysis identified a rare missense mutation in the gene encoding pancreas-specific protease Elastase 3B (CELA3B) that cosegregates with disease. Studies of the mutant protein in vitro, in cell lines and in CRISPR-Cas9 engineered mice indicate that this mutation causes translational upregulation of CELA3B, which upon secretion and activation by trypsin leads to uncontrolled proteolysis and recurrent pancreatitis. Although lesions in several other pancreatitic proteases have been previously linked to hereditary pancreatitis, this is the first known instance of a mutation in CELA3B and a defect in translational control contributing to this disease.

COPA mutations impair ER-Golgi transport and cause hereditary autoimmune-mediated lung disease and arthritis.

Unbiased genetic studies have uncovered surprising molecular mechanisms in human cellular immunity and autoimmunity. We performed whole-exome sequencing and targeted sequencing in five families with an apparent mendelian syndrome of autoimmunity characterized by high-titer autoantibodies, inflammatory arthritis and interstitial lung disease. We identified four unique deleterious variants in the COPA gene (encoding coatomer subunit α) affecting the same functional domain. Hypothesizing that mutant COPA leads to defective intracellular transport via coat protein complex I (COPI), we show that COPA variants impair binding to proteins targeted for retrograde Golgi-to-ER transport. Additionally, expression of mutant COPA results in ER stress and the upregulation of cytokines priming for a T helper type 17 (TH17) response. Patient-derived CD4(+) T cells also demonstrate significant skewing toward a TH17 phenotype that is implicated in autoimmunity. Our findings uncover an unexpected molecular link between a vesicular transport protein and a syndrome of autoimmunity manifested by lung and joint disease.

Insights into type 1 diabetes from the autoimmune polyendocrine syndromes.

PURPOSE OF REVIEW: Advances in human genetics and investigations in animal models of autoimmune disease have allowed insight into the basic mechanisms of immunologic tolerance. These advances allow us to understand the pathogenesis of type 1 diabetes and other autoimmune diseases as never before. Here, we discuss the tolerance mechanisms of the autoimmune polyendocrine syndromes and their relevance to type 1 diabetes. RECENT FINDINGS: Defects in central tolerance with alteration of self-antigen expression levels in the thymus are a potent cause of autoimmunity. Peripheral tolerance defects that alter T-cell activation and signaling also play an important role in the pathogenesis of diabetes and other associated autoimmune disorders, with multiple modest defects working in concert to produce disease. Regulation of the immune response through the action of regulatory T cells is a potent mode of tolerance induction in autoimmunity that is important in type 1 diabetes. SUMMARY: Rare syndromes of autoimmunity provide a valuable window into the breakdown of tolerance and identify multiple checkpoints that are critical for generation of autoimmunity. Understanding the application of these in type 1 diabetes will allow the development of future immunomodulatory therapies in the treatment and prevention of disease.

Protein microarray analysis reveals BAFF-binding autoantibodies in systemic lupus erythematosus.

Autoantibodies against cytokines, chemokines, and growth factors inhibit normal immunity and are implicated in inflammatory autoimmune disease and diseases of immune deficiency. In an effort to evaluate serum from autoimmune and immunodeficient patients for Abs against cytokines, chemokines, and growth factors in a high-throughput and unbiased manner, we constructed a multiplex protein microarray for detection of serum factor-binding Abs and used the microarray to detect autoantibody targets in SLE. We designed a nitrocellulose-surface microarray containing human cytokines, chemokines, and other circulating proteins and demonstrated that the array permitted specific detection of serum factor-binding probes. We used the arrays to detect previously described autoantibodies against cytokines in samples from individuals with autoimmune polyendocrine syndrome type 1 and chronic mycobacterial infection. Serum profiling from individuals with SLE revealed that among several targets, elevated IgG autoantibody reactivity to B cell-activating factor (BAFF) was associated with SLE compared with control samples. BAFF reactivity correlated with the severity of disease-associated features, including IFN-α-driven SLE pathology. Our results showed that serum factor protein microarrays facilitate detection of autoantibody reactivity to serum factors in human samples and that BAFF-reactive autoantibodies may be associated with an elevated inflammatory disease state within the spectrum of SLE.

BPIFB1 is a lung-specific autoantigen associated with interstitial lung disease.

Interstitial lung disease (ILD) is a complex and heterogeneous disorder that is often associated with autoimmune syndromes. Despite the connection between ILD and autoimmunity, it remains unclear whether ILD can develop from an autoimmune response that specifically targets the lung parenchyma. We examined a severe form of autoimmune disease, autoimmune polyglandular syndrome type 1 (APS1), and established a strong link between an autoimmune response to the lung-specific protein BPIFB1 (bactericidal/permeability-increasing fold-containing B1) and clinical ILD. Screening of a large cohort of APS1 patients revealed autoantibodies to BPIFB1 in 9.6% of APS1 subjects overall and in 100% of APS1 subjects with ILD. Further investigation of ILD outside the APS1 disorder revealed BPIFB1 autoantibodies present in 14.6% of patients with connective tissue disease-associated ILD and in 12.0% of patients with idiopathic ILD. The animal model for APS1, Aire⁻/⁻ mice, harbors autoantibodies to a similar lung antigen (BPIFB9); these autoantibodies are a marker for ILD. We found that a defect in thymic tolerance was responsible for the production of BPIFB9 autoantibodies and the development of ILD. We also found that immunoreactivity targeting BPIFB1 independent of a defect in Aire also led to ILD, consistent with our discovery of BPIFB1 autoantibodies in non-APS1 patients. Overall, our results demonstrate that autoimmunity targeting the lung-specific antigen BPIFB1 may contribute to the pathogenesis of ILD in patients with APS1 and in subsets of patients with non-APS1 ILD, demonstrating the role of lung-specific autoimmunity in the genesis of ILD.

Mechanisms and models of immune tolerance breakdown in the ovary.

Ovarian autoimmunity is increasingly implicated in the etiology of primary ovarian insufficiency (POI), previously termed PREMATURE OVARIAN FAILURE or PREMATURE MENOPAUSE. Links to autoimmunity in human POI have long been noted due to the close association of POI with several autoimmune diseases and syndromes such as Addison's disease and Autoimmune polyglandular syndrome 1. However, diagnosis of autoimmune-mediated POI (aPOI) remains challenging because of the lack of sensitive or specific markers of disease. Autoimmunity can arise from the breakdown of immunological tolerance in several ways. How then may we discern what constitutes a relevant target and what represents a downstream phenomenon? The answer lies in the study of pathogenic mechanisms in translational models of disease. From examples in humans and mice, we see that ovarian autoimmunity likely arises from a limited number of antigens targeted in the ovary that are organ specific. These antigens may be conserved but not limited to those seen in animal models of autoimmune ovarian disease. Recent advances in these areas have begun to define the relevant antigens and mechanisms of immune tolerance breakdown in the ovary. Work in translational models continues to provide insight into mechanisms of disease pathogenesis that will allow more accurate diagnosis and, ultimately, improved interventions for women with aPOI.

Autoimmune oophoritis with multiple molecular targets mitigated by transgenic expression of mater.

Primary ovarian insufficiency (POI) resulting from ovarian autoimmunity is a poorly understood clinical condition lacking in effective treatments. Understanding the targets of the autoimmune response and induction of ovarian-specific tolerance would allow development of focused therapies to preserve fertility in an at-risk population. MATER (maternal antigen that embryos require) is a known ovarian autoantigen targeted in autoimmune syndromes of POI. We attempt to induce ovarian-specific tolerance via transgenic expression of the MATER antigen on potentially tolerogenic antigen-presenting cells (APC), which typically present antigen via the major histocompatibility complex (MHC) class II molecule. We hypothesize that expression of MATER in a MHC class II-dependent manner on APC can mediate induction of ovarian tolerance. We utilized a well-characterized murine model of ovarian autoimmunity, whereby oophoritis develops after d 3 neonatal thymectomy (NTx). Wild-type and transgenic mice, carrying an MHC Class II-driven Mater gene (IE-Mater), were subjected to NTx and assessed for evidence of autoimmune oophoritis. After disease induction by NTx, female mice carrying the IE-Mater transgene had significant reductions in histological oophoritis (56%) and circulating ovarian autoantibodies (28%) compared with wild-type females (94% and 82%, respectively). Incidence of other autoimmunity was unaffected as assessed by antinuclear autoantibodies. Transgenic expression of MATER in APC can induce antigen-specific tolerance with a significant reduction in ovarian autoimmunity. Lack of complete disease protection suggests that other antigens may also play a role in autoimmune oophoritis. As a known autoantigen in the human APS1 (autoimmune polyglandular syndrome type 1), which is associated with POI, MATER may represent a relevant target for future diagnostic and therapeutic clinical interventions.

What's new in the Aire?

Unraveling the mechanisms underlying autoimmune disease remains a difficult challenge. Recent lessons learned from the study of AIRE (autoimmune regulator), the gene responsible for the rare monogenic human syndrome APS-1, highlight the power of genetics to reveal disease pathogenesis. With the discovery of AIRE, central tolerance has re-emerged as a crucial check against autoimmunity. Aire-mediated regulation of diverse self-antigens in the thymus serves as a paradigm for the importance of promiscuous gene expression in the prevention of autoimmune disease. Recent characterization of Aire-targeted antigens continues to bear this out. Here, we review the current progress surrounding the role of Aire in central tolerance from a molecular, genetic and developmental basis.