IgA-containing Immune Complexes Research Articles

Effect of Telitacicept on Circulating Gd-IgA1 and IgA-Containing Immune Complexes in IgA Nephropathy

IntroductionTelitacicept, a transmembrane activator and cyclophilin ligand (CAML) interactor (TACI) fusion protein targeting B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL), has proven efficacy in treating Immunoglobulin A (IgA) nephropathy. However, serum biomarkers that could predict the clinical response during the treatment remain unclear. MethodsPlasma samples from 24 participants in the Phase 2 clinical trial were collected at baseline and after 4, 12, and 24 weeks, and 8 participants in the placebo group, 9 in the 160 mg group, and 7 in the 240 mg group. We measured the levels of Galactose deficient-IgA1(Gd-IgA1) , IgA-containing immune complexes, C3a, C5a, and sC5b-9. The association between the changes in these markers and proteinuria reduction was analyzed. ResultsAfter 24 weeks of treatment, Gd-IgA1 decreased by 43.9% (95% CI: 29.8%, 55.1%), IgG-IgA immune complex by 31.7% (14.4%, 45.5%), and poly-IgA immune complex by 41.3% (6.5%, 63.1%) in the 160 mg group; Gd-IgA1 decreased by 50.4% (38.6%, 59.9%), IgG-IgA immune complex decreased by 42.7% (29.5%, 53.4%), and poly-IgA immune complex decreased by 67.2% (48.5%,79.1%) in the 240 mg group. There were no significant changes in the circulatory C3a, C5a, or sC5b-9 levels during telitacicept treatment. Decreases in both plasma Gd-IgA1 and IgG-IgA or poly-IgA immune complexes were associated with proteinuria reduction. In turn, IgG-IgA or poly-IgA immune complexes showed a dose-dependent effect, consistent with proteinuria reduction during telitacicept treatment1. ConclusionTelitacicept lowered both circulating Gd-IgA1 and IgA-containing immune complexes, while IgA immune complex levels were more consistent with decreased proteinuria.

Practical Considerations for the Use of Sparsentan in the Treatment of Patients with IgAN in Clinical Practice.

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. It is characterized by the mesangial deposition of IgA-containing immune complexes, triggering damage to the glomerular filtration barrier that is amplified by the tandem action of endothelin-1 and angiotensin II at their receptors. Proteinuria and progressive glomerular damage cause loss of kidney function in up to 50% of patients within 10-20 years. The risk of progression is strongly associated with persistent proteinuria (>0.75-1 g/day). Current standard of care involves interventions to decrease proteinuria and control blood pressure. Immunosuppressive agents, used in selected patients at high risk for progression, can be associated with significant side effects. Sparsentan, a novel non-immunosuppressive single-molecule Dual Endothelin Angiotensin Receptor Antagonist (DEARA), received FDA accelerated approval based on interim results from the PROTECT trial, which demonstrated that sparsentan-treated patients achieved a significantly greater reduction in proteinuria from baseline versus the active control irbesartan and that sparsentan was generally safe and well tolerated. Sparsentan is the first non-immunosuppressive treatment to be FDA-approved for the reduction of proteinuria in adults with IgAN at high risk of disease progression. We provide practical guidance for the clinical use of sparsentan in adults with IgAN.

Treatment of IgA Nephropathy: A Rapidly Evolving Field.

The pivotal event in the pathophysiology of IgA nephropathy is the binding of circulating IgA-containing immune complexes to mesangial cells, with secondary glomerular and tubulointerstitial inflammation and fibrosis. The paramount difficulty in the management of IgA nephropathy is the heterogeneity in its clinical presentation and prognosis, requiring an individualized treatment approach. Goal-directed supportive care remains the bedrock of therapy for all patients, regardless of risk of progression. Sodium-glucose transporter 2 inhibitors and sparsentan should be integral to contemporary supportive care, particularly in patients with chronic kidney damage. Pending the development of reliable biomarkers, it remains a challenge to identify patients prone to progression due to active disease and most likely to derive a net benefit from immunosuppression. The use of clinical parameters, including the degree of proteinuria, the presence of persistent microscopic hematuria, and the rate of eGFR loss, combined with the mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, crescents score, is currently the best approach. Systemic glucocorticoids are indicated in high-risk patients, but the beneficial effects wane after withdrawal and come at the price of substantial treatment-associated toxicity. Therapies with direct effect on disease pathogenesis are increasingly becoming available. While targeted-release budesonide has garnered the most attention, anti-B-cell strategies and selective complement inhibition will most likely prove their added value. We propose a comprehensive approach that tackles the different targets in the pathophysiology of IgA nephropathy according to their relevance in the individual patient.

EPH40 A Retrospective Cohort Study of Veteran′s Affairs Data: Epidemiology, Treatments, Clinical Outcomes, and Burden of Immunoglobulin a Nephropathy

Immunoglobulin A nephropathy (IgAN), the glomerular accumulation of IgA-containing immune complexes in the kidneys, may lead to damage of the glomerular filtration barrier which results in proteinuria, hematuria, and often kidney failure (KF). This study describes the epidemiology, treatments, clinical outcomes, and resource burden of patients with IgAN using United States Veteran’s Affairs (VA) data.

IgA Nephropathy: Current Understanding and Perspectives on Pathogenesis and Targeted Treatment.

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, with varied clinical and histopathological features between individuals, particularly across races. As an autoimmune disease, IgAN arises from consequences of increased circulating levels of galactose-deficient IgA1 and mesangial deposition of IgA-containing immune complexes, which are recognized as key events in the widely accepted "multi-hit" pathogenesis of IgAN. The emerging evidence further provides insights into the role of genes, environment, mucosal immunity and complement system. These developments are paralleled by the increasing availability of diagnostic tools, potential biomarkers and therapeutic agents. In this review, we summarize current evidence and outline novel findings in the prognosis, clinical trials and translational research from the updated perspectives of IgAN pathogenesis.

FC050: Nefecon® Selectively Modifies the Composition of Circulating Immune Complexes in IGA Nephropathy

Abstract BACKGROUND AND AIMS IgA nephropathy (IgAN) is characterized by the mesangial deposition of IgA-containing immune complexes (IgA-IC). There is, however, no clear association between extent of mesangial IgA-IC deposition and disease severity in IgAN, suggesting that the composition of the IgA-IC, rather than the actual amount, may be critical in determining pathogenic consequences. The NEFIGAN trial (NCT01738035) assessed the safety and efficacy of a novel targeted-release formulation of budesonide (Nefecon®), designed to deliver the drug to the gut-associated lymphoid tissue (GALT)-rich distal ileum in patients with IgAN. The trial comprised a 6-month run-in, a 9-month treatment and a 3-month follow-up phase. A total of 48 patients received Nefecon® 16 mg/day, 51 patients received Nefecon® 8 mg/day and 50 patients received placebo. The key result of the study was that Nefecon® 16 mg/day, added to optimized renin–angiotensin system blockade, reduced proteinuria and stabilized estimated glomerular filtration rate in patients with IgAN. These findings have now been replicated in the NefIgArd study, which released data in 2021. Here, we report the composition of IgA-IC in the serum of patients treated with Nefecon® 16 mg/day or placebo in the NEFIGAN trial, assessed using liquid chromatography with tandem mass spectrometry (LC-MS/MS). This study was supported by a grant from Calliditas Therapeutics AB. METHOD Using Jacalin Agarose and elution with 0.1 M d-galactose, IgA-ICs were affinity-purified from serum of patients who received placebo (n=18) or Nefecon® 16 mg/day (n=18) at the start of treatment (SOT) and end of treatment (EOT). All protein samples were reduced and alkylated prior to digestion with trypsin, dried using a Savant SpeedVac (Thermo Fisher Scientific, UK) and dissolved in 40 µL of 0.1% formic acid. Each sample, spiked with iRT standard peptides (Biognosys, Switzerland), was loaded onto an Evotip (Evosep Biosystems, Denmark) column. Mass spectrometry analyses were performed on the Evosep One (Evosep) platform, coupled to the TIMS TOF Pro (Bruker, US). For protein identification and quantification, raw data were processed with FragPipe (V16), based on at least two peptides per protein. The protein intensities thus generated were Log_2-transformed and internally normalized using IGHA1 protein as standard. For each patient, the normalized protein amount at SOT was subtracted from the amount at EOT. A probabilistic dropout model was applied to the data to estimate fold changes between treatment and placebo groups at EOT. The proteins were ranked using t-statistic, and a gene set enrichment analysis was performed to determine the gene sets significantly affected by Nefecon® 16 mg/day versus placebo. RESULTS Gene ontology analysis revealed that treatment with Nefecon® 16 mg/day led to a significant protein enrichment in IgA-IC associated with pathways driving biological processes involved in the negative regulation of gene expression and transcription, gene silencing and epigenetics. In parallel, treatment with Nefecon® was also associated with an enrichment of proteins associated with extracellular vesicle and exosome formation. CONCLUSION For the first time, we show that it is possible to pharmacologically modify the composition of circulating IgA-IC in IgAN. Treatment with Nefecon® 16 mg/day for 9 months selectively altered the protein composition of IgA-IC in a way that is likely to have significant consequences on the downstream mesangial response to IgA-IC accumulation; this may, in part, explain the antiproteinuric effect of this approach and the longer-term kidney function protection that has been reported in both the NEFIGAN and NefIgArd clinical trials. Studies are ongoing to precisely delineate the impact of these compositional changes on the pathogenicity of IgA-IC in IgAN.

IgA and FcαR are critical components of plasmacytoid DC response to autoantibody-containing immune complexes in SLE.

Abstract Systemic lupus erythematosus (SLE) is a heterogenous autoimmune disease characterized by the presence of circulating autoreactive anti-nuclear antibodies (ANAs). ANAs form immune complexes (ICs) upon binding to nuclear antigens and these ANA-ICs promote a feedforward loop by enhancing immune responses in cells that recognize ANA-ICs via Fc receptors (FcRs). Plasmacytoid dendritic cells (pDCs) are FcR expressing cells that promote SLE pathology. ANA-ICs deliver nucleic acids to endosomal TLR7 and TLR9. These TLRs induce type I IFN secretion and immune activation upon nucleic acid recognition. Type I IFNs, including IFNα, and interferon stimulated genes are correlated with SLE disease activity. IgG isotype facilitated ANA-IC internalization via FcgRIIA has been the most studied antibody-mediated route for IFNα production in pDCs. The importance of IgA isotype ANAs remains under investigated despite these autoantibodies being present in half of SLE patients. We show here the novel result that human pDCs express the IgA-specific FcαR (CD89) by flow cytometry, that pDCs from SLE patients express increased FcαR compared to pDCs from healthy controls, and that increased pDC FcαR expression in SLE correlates with hallmark IFNα gene set. Additionally, we found that IgA autoantibodies were a critical component of pDC ANA-IC activation when these ANA-IC were generated with serum from IgA autoantibody positive SLE donors complexed with smRNP nuclear antigen. Therefore, our study shows that IgA-containing immune complexes and FαRI are important contributors to pDC type I IFN production in SLE. Supported by LRA Lupus Mechanisms and Targets Award (JAH), R21AI154841 (JAH), and ITHS TL1 training grant (HRW).

New Insights and Challenges Associated With IgA Vasculitis and IgA Vasculitis With Nephritis-Is It Time to Change the Paradigm of the Most Common Systemic Vasculitis in Childhood?

What are the challenges ahead and how have we responded so far when it comes to the non-granulomatous systemic vasculitis, characterized mainly by deposits of IgA immune complexes in the endothelium of small blood vessels—IgA vasculitis (IgAV)? That is the question to which we tried to answer. We summarized existing knowledge about epidemiology, pathogenesis, genetics, diagnostic tests and therapy in this somewhat neglected entity in pediatric rheumatology. Since etiopathogenesis of IgA vasculitis is complex, with factors other than galactose-deficient IgA1-containing immune complexes also being important, and may involve numerous interactions between environmental and genetic factors, genomics alone cannot explain the entirety of the risk for the disease. The incidence of IgAV and nephritis varies worldwide and may be a consequence of overlapping genetic and environmental factors. In addition to the role of the HLA class II genes, some studies have pointed to the importance of non-HLA genes, and modern geostatistical research has also indicated a geospatial risk distribution, which may suggest the strong influence of different environmental factors such as climate, pathogen load, and dietary factors. The application of modern geostatistical methods until recently was completely unknown in the study of this disease, but thanks to the latest results it has been shown that they can help us a lot in understanding epidemiology and serve as a guide in generating new hypotheses considering possible environmental risk factors and identification of potential genetic or epigenetic diversity. There is increasing evidence that an integrative approach should be included in the understanding of IgA vasculitis, in terms of the integration of genomics, proteomics, transcriptomics, and epigenetics. This approach could result in the discovery of new pathways important for finding biomarkers that could stratify patients according to the risk of complications, without an invasive kidney biopsy which is still the gold standard to confirm a diagnosis of nephritis, even if biopsy findings interpretation is not uniform in clinical practice. Ultimately, this will allow the development of new therapeutic approaches, especially important in the treatment of nephritis, for which there is still no standardized treatment.

Sialylation of IgG inhibits the formation of galactose-deficient IgA1-containing immune complexes and protects mesangial cells from injury in IgA nephropathy

BackgroundThe addition of sialic acid alters IgG from a pro-inflammatory state to an anti-inflammatory state. However, there is a lack of research on the changes of IgG sialylation in IgA nephropathy (IgAN).MethodsThis study included a total of 184 IgAN patients. The sialylated IgG (SA-IgG), IgG-galactose-deficient IgA1 complex (IgG-Gd-IgA1-IC), IL-6, TNF-α, and TGF-β were detected using commercial ELISA kits. SA-IgG, non-sialylated IgG (NSA-IgG), sialylated IgG-IgA1 complex (SA-IgG-IgA1), and non-sialylated IgG-IgA1 complex (NSA-IgG-IgA1) were purified from IgAN patients and healthy controls (HCs).ResultsThe mean SA-IgG levels in plasma and B lymphocytes in IgAN patients were significantly higher than those of healthy controls. A positive correlation was found between SA-IgG levels in plasma and B lymphocytes. In vitro, the results showed that the release of IgG-Gd-IgA1-IC was significantly decreased in peripheral blood mononuclear cells (PBMCs) cultured with SA-IgG from both IgAN patients and healthy controls. The proliferation ability and the release of IL-6, TNF-α, and TGF-β in human mesangial cells (HMCs) were measured after stimulating with SA-IgG-IgA1-IC and NSA-IgG-IgA1-IC. The mesangial cell proliferation levels induced by NSA-IgG-IgA1-IC derived from IgAN patients were significantly higher than those caused by SA-IgG-IgA1-IC derived from IgAN patients and healthy controls. Compared with NSA-IgG-IgA1 from healthy controls, IgAN-NSA-IgG-IgA1 could significantly upregulate the expression of IL-6 and TNF-α in mesangial cells. The data showed that there weren’t any significant differences in the levels of IL-6, TNF-α, and TGF-β when treated with IgAN-SA-IgG-IgA1 and HC-NSA-IgG-IgA1.ConclusionsThe present study demonstrated that the sialylation of IgG increased in patients with IgA nephropathy. It exerted an inhibitory effect on the formation of Gd-IgA1-containing immune complexes in PBMCs and the proliferation and inflammation activation in mesangial cells.

Molecular insights into the early stage of glomerular injury in IgA nephropathy using single-cell RNA sequencing

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and defined by the presence of IgA-containing immune complexes in the mesangium that induce an inflammation leading to glomerulonephritis. Since we poorly understand early mechanisms of glomerular injury in IgAN we performed single-cell RNA sequencing (scRNA-seq) analysis of glomerulus-associated cells using SMARTseq2-technology at the early stage of IgAN in grouped ddY-mice. Cell-specific molecular signatures unraveled a key role of endothelial cells in the early pathogenesis of IgAN, especially in the recruitment and infiltration of immune cells. Mesangial and podocyte cells demonstrated less molecular changes. Several intra-glomerular paracrine pathways were detected, such as mesangial cell-derived Slit3 potentially activating Robo-receptors in podocyte/endothelial cells. Surprisingly, proximal tubular cells were strongly affected at the early stage and potential glomerulo-tubular cell-cell crosstalk pathways were identified. Importantly, many of the cellular transcriptomic signatures identified in this well-established mouse model were also detected in published bulk transcriptomic data in human IgAN. Moreover, we validated the functionality of key cell-cell crosstalk pathways using cell culture models, such as the effect of the Slit-Robo signalling axis. Thus, our study provides important novel molecular insights into the pathogenesis of early IgAN-associated glomerulopathy.

Collectin11 and Complement Activation in IgA Nephropathy.

IgA nephropathy is the most common primary GN worldwide. Previous research demonstrated that collectin11, an initiator of the complement lectin pathway, was involved in both AKI and chronic tubulointerstitial fibrosis. Here, we investigated the potential role of collectin11 in the pathogenesis of IgA nephropathy. The deposition of collectin11 and other complement proteins was detected in glomeruli of 60 participants with IgA nephropathy by immunofluorescence. In vitro, human mesangial cells were treated with IgA1-containing immune complexes derived from participants with IgA nephropathy. Then, the expression of collectin11 in mesangial cells was examined by quantitative RT-PCR and immunofluorescence. The codeposition of collectin11 with IgA1 or C3 on mesangial cells was detected by immunofluorescence and proximity ligation assays. In total, 37% of participants with IgA nephropathy (22 of 60) showed codeposition of collectin11 with IgA in the glomerular mesangium. Using an injury model of mesangial cells, we demonstrated that IgA1-immune complexes derived from participants with IgA nephropathy increased the secretion of collectin11 in mesangial cells with the subsequent deposition of collectin11 on the cell surface via the interaction with deposited IgA1-immune complexes. In vitro, we found that collectin11 bound to IgA1-immune complexes in a dose-dependent but calcium-independent manner. Furthermore, deposited collectin11 initiated the activation of complement and accelerated the deposition of C3 on mesangial cells. In situ-produced collectin11 by mesangial cells might play an essential role in kidney injury in a subset of patients with IgA nephropathy through the induction of complement activation.

Dermatologic Manifestations of Systemic Diseases in Childhood

Dermatologic Manifestations of Systemic Diseases in Childhood

Elevated Myeloperoxidase-DNA Complex Levels in Sera of Patients with IgA Vasculitis

Introduction: IgA vasculitis is a systemic disease that results from the entrapment of circulating IgA-containing immune complexes in small-vessel walls in the skin, kidneys, and gastrointestinal tract. An excessive formation of neutrophil extracellular traps (NETs) is involved in the pathogenesis of vasculitis, especially in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. This study aimed to clarify whether NETs are implicated in IgA vasculitis. Methods: Twenty-two patients with IgA vasculitis and 4 healthy volunteers were enrolled in this study. Serum levels of myeloperoxidase (MPO)-DNA complex, a fragment derived from NETs, were determined by enzyme-linked immunosorbent assay (ELISA), and the association between MPO-DNA complex levels and clinical parameters was examined. The presence of the ANCA was also assessed by ELISA specific for MPO and proteinase 3 (PR3) and indirect immunofluorescence (IIF), followed by assessing the differences in clinical parameters with and without the ANCA. Results: Serum MPO-DNA complex levels were significantly higher in patients with IgA vasculitis than those in healthy controls. A significant positive correlation between the serum MPO-DNA complex and IgA levels was noted. Interestingly, 63.6% of IgA vasculitis patients were ANCA-positive in IIF with an atypical pattern, whereas neither MPO-ANCA nor PR3-ANCA was detected by ELISA. These findings indicated that some IgA vasculitis patients possessed the so called minor ANCA. Serum IgA and MPO-DNA complex levels and the frequency of hematuria in the minor ANCA-positive group were significantly higher than in the minor ANCA-negative group. Conclusion: The collective findings suggested that NETs are certainly involved in the pathogenesis of IgA vasculitis.

Aberrantly Glycosylated IgA1 in IgA Nephropathy: What We Know and What We Don't Know.

IgA nephropathy (IgAN), the most common primary glomerular disease worldwide, is characterized by glomerular deposition of IgA1-containing immune complexes. The IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine usually with β1,3-linked galactose and variable sialylation. Circulating levels of IgA1 with abnormally O-glycosylated HR, termed galactose-deficient IgA1 (Gd-IgA1), are increased in patients with IgAN. Current evidence suggests that IgAN is induced by multiple sequential pathogenic steps, and production of aberrantly glycosylated IgA1 is considered the initial step. Thus, the mechanisms of biosynthesis of aberrantly glycosylated IgA1 and the involvement of aberrant glycoforms of IgA1 in disease development have been studied. Furthermore, Gd-IgA1 represents an attractive biomarker for IgAN, and its clinical significance is still being evaluated. To elucidate the pathogenesis of IgAN, it is important to deconvolute the biosynthetic origins of Gd-IgA1 and characterize the pathogenic IgA1 HR O-glycoform(s), including the glycan structures and their sites of attachment. These efforts will likely lead to development of new biomarkers. Here, we review the IgA1 HR O-glycosylation in general and the role of aberrantly glycosylated IgA1 in the pathogenesis of IgAN in particular.

A Pilot Study to Predict Risk of IgA Nephropathy Progression Based on miR-204 Expression

IntroductionImmunoglobulin (Ig)A nephropathy (IgAN) is the most frequently diagnosed primary glomerulonephritis worldwide. Despite the common diagnostic feature of mesangial IgA-containing immune complex deposition, the clinical course of the disease is extremely variable, with 30% of patients developing end-stage kidney disease within 20 years of diagnosis. Therefore, identifying which patients are likely to progress is paramount.ResultsIn this pilot study, we found that urinary exosomal miR-204 expression was significantly reduced in IgAN compared with healthy subjects. However, there was no difference in miR-204 expression between IgAN and non-IgAN chronic kidney disease controls. Analysis of miR-204 expression in kidney biopsy cores by next-generation sequencing followed by quantitative polymerase chain reaction validation in independent cohorts demonstrated that expression of miR-204 was significantly lower in IgAN compared with thin-membrane nephropathy but not compared with membranous nephropathy. Patients with IgAN at high risk of future progression had significantly lower expression of miR-204 than those at low risk of progression. Cortical localization indicated that miR-204 was preferentially expressed in the interstitium compared with glomeruli in IgAN nonprogressors and that this distribution was lost in IgAN progressors. Receiver operating characteristic curve analysis between the 2 IgAN cohorts revealed an area under the curve of 0.82. In addition, miR-204 expression correlated with known clinicopathological prognostic risk factors. Importantly, incorporating miR-204 into the International IgAN risk prediction tool improved the diagnostic power of the algorithm to predict risk of progression.ConclusionAdditional large-scale studies are now needed to validate the additive value of miR-204 in improving risk prediction in IgAN and more broadly in chronic kidney disease.

MO148A MULTI-CENTER, RANDOMIZED, DOUBLE-BLIND, PLACEBO CONTROLLED, PARALLEL GROUP, PHASE III STUDY TO EVALUATE THE EFFICACY AND SAFETY OF LNP023 IN PRIMARY IGA NEPHROPATHY PATIENTS

Abstract Background and Aims IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. It is an autoimmune disease characterized by deposits of IgA1-containing immune complexes in the glomerular mesangium leading to local inflammation and subsequent decline in kidney function. Currently, there are no targeted therapies for IgAN. The KDIGO guidelines (2012) recommend optimized long-term supportive care including inhibition of the RAS (ACEi or ARB) as well as lifestyle modification for blood pressure control and proteinuria reduction. Patients who remain at high risk of progressive CKD despite maximal supportive care might be considered for high-dose corticosteroids or immunosuppressants. In recent years, mounting evidence has supported an important role for complement activation in disease onset and progression of IgAN. The alternative complement pathway (AP) and lectin complement pathway (LP) are found to be activated in 75-90% and 17-25% of IgAN patients, respectively (Floege et al 2014, Maillard et al 2015). Factor B (FB) is an essential component of C3- and C5-convertases. Iptacopan (LNP023) is an oral, first-in-class, highly potent selective inhibitor of FB and thereby blocks the activity of AP C3 and C5 convertases, inhibiting the AP as well as the amplification of the classic and lectin complement pathways. Currently, iptacopan is being evaluated in an ongoing adaptive seamless double-blind and placebo-controlled dose-ranging Phase 2 study (CLNP023X2203, Part 1 and Part 2) in patients with biopsy-confirmed IgAN and elevated proteinuria [urine protein to creatinine ratio (UPCR) ≥ 0.75 g/g]. An interim analysis (IA) at 90 days of treatment in the Part 1 study showed that iptacopan administered up to 200 mg b.i.d for 90 days was safe, well tolerated and may be effective in reducing proteinuria. A further IA combining participants in Part 1 and Part 2 will be completed in early 2021 and the pivotal phase 3 trial is to start in early 2021. Aim APPLAUSE-IgAN (NCT04578834; CLNP023A2301) is a multicenter, randomized, double-blind, placebo-controlled parallel-group Phase 3 study which aims to evaluate the efficacy and safety of iptacopan (LNP023) compared with placebo in addition to supportive therapy on proteinuria reduction and slowing kidney disease progression in primary IgAN patients. Method Adult patients diagnosed with primary IgAN (based on kidney biopsy and elevated proteinuria [UPCR ≥ 1 g/day]) will be recruited. A run-in period will ensure that patients have received ACEi/ARB at a maximally tolerated dose for at least 90 days and receive required vaccinations at least 2 weeks prior to first dosing. Patients will be randomized in a 1:1 ratio to either iptacopan 200 mg b.i.d or matching placebo for a 24-month treatment period. The trial will enroll approximately 450 participants, aiming for 430 with eGFR ≥30 mL /min/1.73m2 (main study population). About 20 participants with eGFR 20 to <30 mL/min/1.73m2 (severe renal impairment population) will also be enrolled to explore PK and safety of iptacopan in this group, but will not be included in the efficacy analyses. Primary objectives 1) At IA (when approximately 250 patients have completed the 9 months visit): To demonstrate superiority of iptacopan vs. placebo in the reduction of proteinuria. The IA results may be submitted to support accelerated/conditional approval. 2) At final analysis (when approximately 430 patients have completed 24 months of active treatment): to demonstrate superiority of iptacopan vs. placebo in slowing kidney disease progression measured by the annualized total slope of eGFR decline over 24 months. Results Recruitment will start in Q1 2021. Conclusion This trial will evaluate the efficacy of iptacopan, a promising new therapy for IgAN, in reducing proteinuria and slowing loss of kidney function over 2 years.

Lymphocytes sense antibodies through human FCRL proteins: Emerging roles in mucosal immunity.

Members of the Fc receptor-like (FCRL) family modulate B and T cell responses, yet their functional roles remain enigmatic. Nevertheless, FCRL3 promoter polymorphism that alters gene expression has been associated with autoimmune disease risk, indicating physiologic importance. Providing essential functional context, human FCRL3, FCRL4, and FCRL5 have recently been identified as secretory IgA (SIgA), dimeric IgA, and IgG receptors, respectively, revealing novel ways lymphocytes can interact with antibodies. FCRL3 and FCRL4 are able to distinguish the mucosal and systemic origin of IgA-containing immune complexes, respectively, with clear implications in guiding mucosal responses. SIgA can signal mucosal breach through FCRL3, driving the functional plasticity of regulatory T cells toward inflammatory to help control invading pathogens. Conversely, recognition of dimeric IgA by FCRL4 on memory B cells located in mucosa-associated lymphoid tissues could promote tolerance to commensals. Memory B cells that accumulate under conditions of chronic antigen presence frequently express FCRL4 and FCRL5, and antibody ligands could provide functional feedback to the cells. FCRL5 apparently recognizes the age of the IgG molecule, using deamidation as a molecular clock, conceivably playing regulatory roles in chronic antibody responses. A framework of FCRL3, FCRL4, and FCRL5 operating as sensors of antibodies in immune complexes is proposed. Sensing the spatial origin and age of immune complexes can shape lymphocyte functional attributes and inform their participation in mucosal immune responses. The potential contributions of FCRL3 and SIgA to the pathogenesis of autoimmune diseases are discussed.

POS-370 HUMAN RENAL MESANGIAL CELL ACTIVATION INDUCED BY ENDOTHELIN-1 OR IGA NEPHROPATHY PATIENT-DERIVED IMMUNE COMPLEXES IS BLOCKED BY SELECTIVE ETA ANTAGONIST ATRASENTAN

Mesangial cell activation in response to deposition of pathogenic IgA-containing immune complexes is characterized by cellular proliferation and inflammatory cytokine secretion, and is considered the initiating intra-renal event in the pathogenesis of IgA nephropathy (IgAN). The molecular mechanisms have not been well defined. Endothelin (ET) pathway activation has been observed in kidney biopsies of IgAN patients and may be an important driver of disease progression by promoting proteinuria along with kidney inflammation and fibrosis via ETA receptor activation.

P0347COMPLEMENT FACTOR BB AND FACTOR C4D IN IGA NEPHROPATHY AND IGA VASCULITIS

Abstract Background and Aims IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide. IgAN and IgA Vasculitis with nephritis (IgAVN) are thought to have related pathogenesis characterized by IgA-containing renal immune complexes contributing to chronic kidney disease (CKD) and renal failure. In both diseases, IgA1 immune complexes and complement factors have been shown to be involved, indicating complement activation. However, the individual contribution of the alternative and lectin pathway has of yet not been fully elucidated. Plasma Bb is a marker of the alternative pathway activity and plasma C4d of the mannan-binding lectin pathway. We aimed to investigate the association between circulating plasma Bb and C4d at diagnosis and potential correlates with clinical features, renal histopathology and renal outcome in patients with IgAN and IgAVN. Method A prospective study of 98 patients undergoing renal biopsy was performed. Median age was 43 years, 52% males, 88% were caucasians, Sixty-six patients were diagnosed with IgAN, 15 IgAVN and 17 controls with “non-immunocomplex driven disease including Thin membrane disease, Diabetic Nephropathy, Minimal change disease or renal failure due to hyperfiltration. Blood samples were analyzed for complement factors C4d and Bb (both ELISA, Termo Fisher ScientificTM). Oxford classification of the renal biopsy was done at baseline and creatinine, estimated glomerular filtration rate (eGFR-CKD-EPI formula) were measured annually. Continuous data are expressed as median (25th to 75th percentile) and nominal or ordinal data as percentage. Comparisons between groups were assessed with the non-parametric Wilcoxon test/ Kruskal-Wallis ANOVA-test for continuous variables and Chi-square test for nominal variables. Results Patients with IgAN and IgAVN were significantly younger than the control group. There were no significant differences between the three groups for gender distribution and eGFR. Complement factor Bb for patients with IgAN and IgAVN was significantly increased (figure 1) as compared to the control group, whereas there was was no statistical difference for complement factorsC4d between groups. Estimated GFR decreased significantly only in patients with IgAN after 24 months of follow-up (56.6 ± 3.8 ml/min/1,73m2 as compared to IgAVN 83.8 ± 8.5 and controls 90.2 ± 8.9). Patients with IgAN had more severe histopathological changes in T-score (T-score 0, 1, 2 in IgAN 51 %, 37 % and 12 % respectively) compared to IgAVN. In the IgAN group a more severe T-score was significantly associated with increased levels of complement factor Bb (p=0.005) but did not reach significance for complement factor C4d (p=0.097). No other difference or correlations were found with regards to M, E, S and C % scores. Conclusion Patients with IgAN were younger and had increased levels of complement factor Bb and after 24 months follow-up significantly reduced eGFR. The increase in factor Bb was also associated with more severe histopathological changes in T-score. These findings suggest that the alternative complement pathway contributes to the pathogenesis in IgAN and chronic kidney damage. Our findings should motivate studies in a larger population to further clarify the role of complement activity in IgAN and IgAVN.

Analysis of O-glycoforms of the IgA1 hinge region by sequential deglycosylation

A common renal disease, immunoglobulin A (IgA) nephropathy (IgAN), is associated with glomerular deposition of IgA1-containing immune complexes. IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine with β1,3-linked galactose and variable sialylation. IgA1 glycoforms with some galactose-deficient (Gd) HR O-glycans play a key role in IgAN pathogenesis. The clustered and variable O-glycans make the IgA1 glycomic analysis challenging and better approaches are needed. Here, we report a comprehensive analytical workflow for IgA1 HR O-glycoform analysis. We combined an automated quantitative analysis of the HR O-glycopeptide profiles with sequential deglycosylation to remove all but Gd O-glycans from the HR. The workflow was tested using serum IgA1 from healthy subjects. Twelve variants of glycopeptides corresponding to the HR with three to six O-glycans were detected; nine glycopeptides carried up to three Gd O-glycans. Sites with Gd O-glycans were unambiguously identified by electron-transfer/higher-energy collision dissociation tandem mass spectrometry. Extracted ion chromatograms of isomeric glycoforms enabled quantitative assignment of Gd sites. The most frequent Gd site was T236, followed by S230, T233, T228, and S232. The new workflow for quantitative profiling of IgA1 HR O-glycoforms with site-specific resolution will enable identification of pathogenic IgA1 HR O-glycoforms in IgAN.