A Proliferation Inducing Ligand (APRIL) targeted antibody is a safe and effective treatment of murine IgA nephropathy

Drugs in Development to Treat IgA Nephropathy

IgA nephropathy is a common glomerulonephritis consequent to the autoimmune response to aberrant glycosylated immunoglobulin (Ig) A antibodies. Although it has historically been considered a benign disease, it has since become clear that a substantial percentage of patients reach end-stage kidney failure over the years. Several therapeutic attempts have been proposed, with systemic steroids being the most prevalent, albeit burdened by possible serious adverse events. Thanks to the more in-depth knowledge of the pathogenesis of IgA nephropathy, new treatment targets have been identified and new drugs developed. In this narrative review, we summarise the molecules under clinical development for the treatment of IgA nephropathy. As a search strategy, we used PubMed, Google, ClinicalTrials.gov and abstracts from recent international congresses. TRF budesonide and sparsentan are the two molecules at a more advanced stage, just entering the market. Other promising agents are undergoing phase III clinical development. These include anti-APRIL and anti-BLyS/BAFF antibodies and some complement inhibitors. Other new possible strategies include spleen tyrosine kinase inhibitors, anti-CD40 ligands and anti-CD38 antibodies. In an era increasingly characterised by 'personalised medicine' and 'precision therapy' approaches and considering that the potential therapeutic armamentarium for IgA nephropathy will be very broad in the near future, the identification of biomarkers capable of helping the nephrologist to select the right drug for the right patient should be the focus of future studies.

Sibeprenlimab, which neutralizes A PRoliferation Inducing Ligand (APRIL), as a new approach to treating IgA nephropathy

INTRODUCTION

Immunoglobulin A (IgA) nephropathy is a common immune-mediated kidney disease leading to high blood pressure and may progress to kidney failure. None of the present treatments are disease-modifying or prolong life. The levels of A PRoliferation Inducing Ligand (APRIL) are raised in subjects with IgA nephropathy. Sibeprenlimab is a humanized IgG2 monoclonal antibody that binds to, and neutralizes, APRIL.

AREAS COVERED

A phase 2 clinical trial of intravenous sibeprenlimab (VIS649) in IgA nephropathy: NCT04287985. The primary efficacy endpoint was the change from baseline in 24-h protein-to-creatinine ratio at 12 months, and this was reduced by sibeprenlimab. Sibeprenlimab also caused clinical remission in some subjects, stabilized estimated glomerular filtration rate (eGFR), and reduced galactose deficient IgA1, IgA, IgM, and IgG levels without causing any infections or other adverse events.

EXPERT OPINION

Sibeprenlimab is a promising new approach to treating IgA nephropathy. The pharmaceutical company behind sibeprenlimab is also developing it for subcutaneous use, which would have advantages over intravenous use. As IgA nephropathy is a long-term progressive disease, key questions that need to be answered, over a long-time course, with sibeprenlimab are (i) whether its safety is maintained, and (ii) whether it improves clinical outcomes.

Targeted therapy in glomerular diseases

Targeted therapy has emerged as a more precise approach to treat glomerular diseases, focusing on specific molecular or cellular processes that contribute to disease development or progression. This approach complements or replaces traditional immunosuppressive therapy, optimizes supportive care, and provides a more personalized treatment strategy. In this review, we summarize the evolving understanding of pathogenic mechanisms in immune-mediated glomerular diseases and the developing targeted therapies based on these mechanisms. We begin by discussing pan-B-cell depletion, anti-CD20 rituximab, and targeting B-cell survival signaling through the BAFF/APRIL pathway. We also exam specific plasma cell depletion with anti-CD38 antibody. We then shift our focus to complement activation in glomerular diseases, which is involved in antibody-mediated glomerular diseases, such as IgA nephropathy, membranous nephropathy, ANCA-associated vasculitis, and lupus nephritis. Non-antibody-mediated complement activation occurs in glomerular diseases, including C3 glomerulopathy, complement-mediated atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. We discuss specific inhibition of terminal, lectin, and alternative pathways in different glomerular diseases. Finally, we summarize current clinical trials targeting the final pathways of various glomerular diseases, including kidney fibrosis. We conclude that targeted therapy based on individualized pathogenesis should be the future of treating glomerular diseases.

The role of BAFF and APRIL in IgA nephropathy: pathogenic mechanisms and targeted therapies

Immunoglobulin A nephropathy (IgAN), characterized by mesangial deposition of galactose-deficient-IgA1 (Gd-IgA1), is the most common biopsy-proven primary glomerulonephritis worldwide. Recently, an improved understanding of its underlying pathogenesis and the substantial risk of progression to kidney failure has emerged. The "four-hit hypothesis" of IgAN pathogenesis outlines a process that begins with elevated circulating levels of Gd-IgA1 that trigger autoantibody production. This results in the formation and deposition of immune complexes in the mesangium, leading to inflammation and kidney injury. Key mediators of the production of Gd-IgA1 and its corresponding autoantibodies are B-cell activating factor (BAFF), and A proliferation-inducing ligand (APRIL), each playing essential roles in the survival and maintenance of B cells and humoral immunity. Elevated serum levels of both BAFF and APRIL are observed in patients with IgAN and correlate with disease severity. This review explores the complex pathogenesis of IgAN, highlighting the pivotal roles of BAFF and APRIL in the interplay between mucosal hyper-responsiveness, B-cell activation, and the consequent overproduction of Gd-IgA1 and its autoantibodies that are key features in this disease. Finally, the potential therapeutic benefits of inhibiting BAFF and APRIL in IgAN, and a summary of recent clinical trial data, will be discussed.

A Phase 2 Trial of Sibeprenlimab in Patients with IgA Nephropathy

BACKGROUND

A proliferation-inducing ligand (APRIL) is implicated in the pathogenesis of IgA nephropathy. Sibeprenlimab is a humanized IgG2 monoclonal antibody that binds to and neutralizes APRIL.

METHODS

In this phase 2, multicenter, double-blind, randomized, placebo-controlled, parallel-group trial, we randomly assigned adults with biopsy-confirmed IgA nephropathy who were at high risk for disease progression, despite having received standard-care treatment, in a 1:1:1:1 ratio to receive intravenous sibeprenlimab at a dose of 2, 4, or 8 mg per kilogram of body weight or placebo once monthly for 12 months. The primary end point was the change from baseline in the log-transformed 24-hour urinary protein-to-creatinine ratio at month 12. Secondary end points included the change from baseline in the estimated glomerular filtration rate (eGFR) at month 12. Safety was also assessed.

RESULTS

Among 155 patients who underwent randomization, 38 received sibeprenlimab at a dose of 2 mg per kilogram, 41 received sibeprenlimab at a dose of 4 mg per kilogram, 38 received sibeprenlimab at a dose of 8 mg per kilogram, and 38 received placebo. At 12 months, the geometric mean ratio reduction (±SE) from baseline in the 24-hour urinary protein-to-creatinine ratio was 47.2±8.2%, 58.8±6.1%, 62.0±5.7%, and 20.0±12.6% in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. At 12 months, the least-squares mean (±SE) change from baseline in eGFR was -2.7±1.8, 0.2±1.7, -1.5±1.8, and -7.4±1.8 ml per minute per 1.73 m2 in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. The incidence of adverse events that occurred after the start of administration of sibeprenlimab or placebo was 78.6% in the pooled sibeprenlimab groups and 71.1% in the placebo group.

CONCLUSIONS

In patients with IgA nephropathy, 12 months of treatment with sibeprenlimab resulted in a significantly greater decrease in proteinuria than placebo. (Funded by Visterra; ENVISION ClinicalTrials.gov number, NCT04287985; EudraCT number, 2019-002531-29.).

Safety, Pharmacokinetics, and Pharmacodynamics of Subcutaneous Sibeprenlimab in Healthy Participants

Sibeprenlimab blocks the cytokine "A Proliferation-Inducing Ligand" (APRIL), which may play a key role in immunoglobulin A nephropathy pathogenesis. A phase 1 study of subcutaneous (SC) sibeprenlimab evaluated preliminary safety, tolerability, pharmacokinetics, and pharmacodynamics in healthy participants. This was an open-label, single-ascending-dose study. Twelve participants in each of 4 sequential dosing cohorts received 1 SC dose of sibeprenlimab (200 mg [1×1 mL injection], 400 mg [2×1 mL injections], 400 mg [1×2 mL injection], or 600 mg [1 mL+2 mL injections]) and underwent 16-week follow-up for adverse events, pharmacokinetics, and pharmacodynamics (serum APRIL, immunoglobulin [Ig] levels). Sibeprenlimab in single SC doses of 200-600 mg was slowly absorbed into the systemic circulation, with a median time to maximum serum concentration of approximately 6-10.5 days, and a mean elimination half-life of approximately 8-10 days. Serum APRIL, IgA, IgM, and, to a lesser extent, IgG decreased in a dose-dependent and reversible manner. Maximal reduction in serum IgA was approximately 60% at the 400- and 600-mg doses and 40% at 200 mg. Serum APRIL rapidly decreased to near the lower limit of quantification, and duration of suppression was dose-dependent, with near complete suppression until weeks 4-6 at the 400-mg dose and week 8 at the 600-mg dose. Adverse events occurred in 30/48 (62.5%) participants; none were serious or led to study discontinuation. Sibeprenlimab rapidly and sustainably reduced target APRIL and Ig biomarkers in a dose-dependent and reversible manner, with acceptable preliminary safety and pharmacokinetics.

The contribution of a proliferation-inducing ligand (APRIL) and other TNF superfamily members in pathogenesis and progression of IgA nephropathy

Advances in our understanding of the pathogenesis of immunoglobulin A nephropathy (IgAN) have led to the identification of novel therapeutic targets and potential disease-specific treatments. Specifically, a proliferation-inducing ligand (APRIL) has been implicated in the pathogenesis of IgAN, mediating B-cell dysregulation and overproduction of pathogenic galactose-deficient IgA1 (Gd-IgA1). Animal and clinical studies support the involvement of APRIL in the pathogenesis and progression of IgAN. An elevated level of APRIL is found in IgAN when compared with controls, which correlates with the level of Gd-IgA1 and associates with more severe disease presentation and worse outcomes. Conversely, anti-APRIL therapy reduces pathogenic Gd-IgA1 and IgA immune complex formation and ameliorates the severity of kidney inflammation and injury. Genome-wide association studies in IgAN have identified TNFSF13 and TNFRSF13B, a cytokine ligand-receptor gene pair encoding APRIL and its receptor, respectively, as risk susceptibility loci in IgAN, further supporting the causal role of the APRIL signalling pathway in IgAN. Several novel experimental agents targeting APRIL, including atacicept, telitacicept, zigakibart and sibeprenlimab, are currently under investigation as potential therapies in IgAN. Preliminary results suggest that these agents are well-tolerated, and reduce levels of Gd-IgA1, with corresponding improvement in proteinuria. Further studies are ongoing to confirm the safety and efficacy of anti-APRIL approaches as an effective therapeutic strategy in IgAN.

A PRoliferation-Inducing Ligand (APRIL) in the Pathogenesis of Immunoglobulin A Nephropathy: A Review of the Evidence

A PRoliferation-Inducing Ligand (APRIL), the thirteenth member of the tumor necrosis factor superfamily, plays a key role in the regulation of activated B cells, the survival of long-lived plasma cells, and immunoglobulin (Ig) isotype class switching. Several lines of evidence have implicated APRIL in the pathogenesis of IgA nephropathy (IgAN). Globally, IgAN is the most common primary glomerulonephritis, and it can progress to end-stage kidney disease; yet, disease-modifying treatments for this condition have historically been lacking. The preliminary data in ongoing clinical trials indicate that APRIL inhibition can reduce proteinuria and slow the rate of kidney disease progression by acting at an upstream level in IgAN pathogenesis. In this review, we examine what is known about the physiologic roles of APRIL and evaluate the experimental and epidemiological evidence describing how these normal biologic processes are thought to be subverted in IgAN. The weight of the preclinical, clinical, and genetic data supporting a key role for APRIL in IgAN has galvanized pharmacologic research, and several anti-APRIL drug candidates have now entered clinical development for IgAN. Herein, we present an overview of the clinical results to date. Finally, we explore where more research and evidence are needed to transform potential therapies into clinical benefits for patients with IgAN.

Novel therapeutic approaches in the management of chronic kidney disease: a narrative review

Chronic kidney disease (CKD) remains a pathologic entity with constantly rising incidence and high rates of morbidity and mortality, which are associated with serious cardiovascular complications. Moreover, the incidence of end-stage renal disease tends to increase. The epidemiological trends of CKD warrant the development of novel therapeutic approaches aiming to prevent its development or retard its progression through the control of major risk factors: type 2 diabetes mellitus, arterial hypertension, and dyslipidemia. Contemporary therapeutics such as sodium-glucose cotransporter-2 inhibitors and second-generation mineralocorticoid receptor antagonists are utilized in this direction. Additionally, experimental and clinical studies present novel drug categories that could be employed in managing CKD, such as aldosterone synthesis inhibitors or activators guanylate cyclase, while the role of melatonin should be further tested in the clinical setting. Finally, in this patient population, the use of hypolipidemic agents may provide incremental benefits.

Telitacicept for autoimmune nephropathy

B cells and the humoral immunity are important players in the pathogenesis of autoimmune diseases. BAFF (also known as BLYS) and a proliferation-inducing ligand APRIL are required for the maintenance of the B-cell pool and humoral immunity. BAFF and APRIL can promote B-cell differentiation, maturation, and plasma cell antibody secretion. BAFF/APRIL overexpression has been identified in several autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, IgA nephropathy, etc. Telitacicept, a novel fully human TACI-Fc fusion protein that binds both BAFF and APRIL, was approved in China in March 2021 for the treatment of systemic lupus erythematosus at a recommended dose of 160 mg/w subcutaneously and is in clinical trials for the treatment of multiple indications in other autoimmune diseases. In this review, we explored telitacicept's mechanism of action and clinical data. In addition, the immune features of autoimmune nephropathy were discussed, emphasizing lupus nephritis, IgA nephropathy, and membranous nephropathy.

Identification of IgA autoantibodies targeting mesangial cells redefines the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis, often progressing to renal failure. IgAN is triggered by IgA deposition in the glomerular mesangium by an undefined mechanism. Here, we show that grouped ddY (gddY) mice, a spontaneous IgAN model, produce serum IgA against mesangial antigens, including βII-spectrin. Most patients with IgAN also have serum anti-βII-spectrin IgA. As in patients with IgAN, IgA⁺ plasmablasts accumulate in the kidneys of gddY mice. IgA antibodies cloned from the plasmablasts carry substantial V-region mutations and bind to βII-spectrin and the surface of mesangial cells. These IgAs recognize transfected and endogenous βII-spectrin exposed on the surface of embryonic kidney-derived cells. Last, we demonstrate that the cloned IgA can bind selectively to glomerular mesangial regions in situ. The identification of IgA autoantibody and its antigen in IgAN provides key insights into disease onset and redefines IgAN as a tissue-specific autoimmune disease.

Randomized Phase 2 Trial of Telitacicept in Patients With IgA Nephropathy With Persistent Proteinuria

Introduction

To date, no specific therapies have been approved for immunoglobulin A nephropathy (IgAN) treatment. Telitacicept is a fusion protein composed of transmembrane activator and calcium-modulating cyclophilin ligand interactor and fragment crystallizable portion of immunoglobulin G (IgG), which neutralizes the B lymphocyte stimulator and a proliferation-inducing ligand.

Methods

This phase 2 randomized placebo-controlled trial aimed to evaluate the efficacy and safety of telitacicept in patients with IgAN. Participants with an estimated glomerular filtration rate (eGFR) >35 ml/min per 1.73 m² and proteinuria ≥0.75 g/d despite optimal supportive therapy, were randomized 1:1:1 to receive subcutaneous telitacicept 160 mg, telitacicept 240 mg, or placebo weekly for 24 weeks. The primary end point was the change in 24-hour proteinuria at week 24 from baseline.

Results

Forty-four participants were randomized into placebo (n = 14), telitacicept 160 mg (n = 16), and telitacicept 240 mg (n = 14) groups. Continuous reductions in serum IgA, IgG, and IgM levels were observed in the telitacicept group. Telitacicept 240 mg therapy reduced mean proteinuria by 49% from baseline (change in proteinuria vs. placebo, 0.88; 95% confidence interval, -1.57 to -0.20; P = 0.013), whereas telitacicept 160 mg reduced it by 25% (-0.29; 95% confidence interval, -0.95 to 0.37; P = 0.389). The eGFR remained stable over time. Adverse events (AEs) were similar in all groups. Treatment-emergent AEs were mild or moderate, and no severe AEs were reported.

Conclusion

Telitacicept treatment led to a clinically meaningful reduction in proteinuria in patients with IgAN in the present phase 2 clinical trial. This effect is indicative of a reduced risk for future kidney disease progression.

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.

IgA nephropathy: an overview of drug treatments in clinical trials

INTRODUCTION

IgA nephropathy (IgAN) is the commonest primary glomerulonephritis worldwide and may progress to end-stage kidney disease (ESKD) within a 10-20 year period. Its slowly progressive course has made clinical trials challenging to perform, however the acceptance of proteinuria reduction as a surrogate end point has significantly improved the feasibility of conducting clinical trials in IgAN, with several novel and repurposed therapies currently undergoing assessment. Already, interim results are demonstrating value to some of these, offering great hope to those with IgAN.

AREAS COVERED

This review explores the rationale, candidates, clinical precedents, and trial status of therapies that are currently or have recently been evaluated for efficacy in IgAN. All IgAN trials registered with the U.S. National Library of Medicine; ClinicalTrials.gov were reviewed.

EXPERT OPINION

For the first time, effective treatment options beyond supportive care are becoming available for those with IgAN. This is the culmination of commendable international efforts and signifies a new era for those with IgAN. As more therapies become available, future challenges will revolve around deciding which treatments are most appropriate for individual patients, which is likely to push IgAN into the realm of precision medicine.

Mucosal Immune System Dysregulation in the Pathogenesis of IgA Nephropathy

The mucosal immune system, via a dynamic immune network, serves as the first line of defense against exogenous antigens. Mucosal immune system dysregulation is closely associated with the pathogenesis of immunoglobulin A nephropathy (IgAN), as illustrated by IgAN having the clinical feature of gross hematuria, often concurrent with mucosal infections. Notably, previous studies have demonstrated the efficacy of tonsillectomy and found that a targeted-release formulation of budesonide reduced proteinuria in patients with IgAN. However, it remains unclear how exogenous antigens interact with the mucosal immune system to induce or exacerbate IgAN. Thus, in this review, we focus on the dysregulation of mucosal immune response in the pathogenesis of IgAN.

Autoantibodies - enemies, and/or potential allies?

Autoantibodies are well known as potentially highly harmful antibodies which attack the host via binding to self-antigens, thus causing severe associated diseases and symptoms (e.g. autoimmune diseases). However, detection of autoantibodies to a range of disease-associated antigens has enabled their successful usage as important tools in disease diagnosis, prognosis and treatment. There are several advantages of using such autoantibodies. These include the capacity to measure their presence very early in disease development, their stability, which is often much better than their related antigen, and the capacity to use an array of such autoantibodies for enhanced diagnostics and to better predict prognosis. They may also possess capacity for utilization in therapy, in vivo. In this review both the positive and negative aspects of autoantibodies are critically assessed, including their role in autoimmune diseases, cancers and the global pandemic caused by COVID-19. Important issues related to their detection are also highlighted.

Safety, tolerability, pharmacokinetics and pharmacodynamics of VIS649 (sibeprenlimab), an APRIL-neutralizing IgG2 monoclonal antibody, in healthy volunteers

Introduction

VIS649 (sibeprenlimab), a humanized IgG₂ monoclonal antibody that inhibits APRIL, is being developed as a potential treatment for IgA nephropathy (IgAN). This phase 1, first-in-human, randomized, double-blind, single ascending dose study aimed to evaluate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of VIS649 in healthy adults.

Methods

Participants were randomized to VIS649 (sequential i.v. dosing cohorts: 0.5, 2.0, 6.0, 12.0 mg/kg) or placebo; a further cohort received VIS649 6.0 mg/kg or placebo followed by a tetanus/diphtheria vaccine challenge.

Results

A total of 51 participants were randomized, dosed, and analyzed for safety (7 for each VIS649 dose; 8 for placebo; 10 for VIS649 + vaccine; 5 for placebo + vaccine). There were no serious adverse events (AEs) or AEs leading to study discontinuation. VIS649 had nonlinear PK: half-life increased with dose and drug exposure increased in a greater than dose-proportional manner. Serum APRIL, IgA, galactose-deficient (Gd) IgA₁, IgG, and IgM were reversibly suppressed in a dose-dependent manner, with a dose–response in time to recovery. Tetanus and diphtheria serum IgG titers increased after recall vaccination.

Conclusion

VIS649 was safe, well tolerated, and reversibly suppressed APRIL and various immunoglobulins, without loss of antigen-specific vaccination response. Further clinical development of VIS649 for IgAN is warranted. Trial registration: ClinicalTrials.gov: NCT03719443.

Single-cell RNA-sequencing reveals distinct immune cell subsets and signaling pathways in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common primary glomerulonephritis globally. Increasing evidence suggests the importance of host immunity in the development of IgAN, but its dynamics during the early stage of IgAN are still largely unclear.

RESULTS

Here we successfully resolved the early transcriptomic changes in immune cells of IgAN by conducting single-cell RNA-sequencing (scRNA-seq) with peripheral blood mononuclear cells. The differentially expressed genes (DEGs) between control and IgAN were predominantly enriched in NK cell-mediated cytotoxicity and cell killing pathways. Interestingly, we discovered that the number and cytotoxicity of NK cells are significantly reduced in IgAN patients, where both the number and marker genes of NK cells were negatively associated with the clinical parameters, including the levels of urine protein creatinine ratio (UPCR), serum galactose-deficient IgA1 and IgA. A distinctive B cell subset, which had suppressed NFκB signaling was predominantly in IgAN and positively associated with disease progression. Moreover, the DEGs of B cells were enriched in different viral infection pathways. Classical monocytes also significantly changed in IgAN and a monocyte subset expressing interferon-induced genes was positively associated with the clinical severity of IgAN. Finally, we identified vast dynamics in intercellular communications in IgAN.

CONCLUSIONS

We dissected the immune landscape of IgAN at the single-cell resolution, which provides new insights in developing novel biomarkers and immunotherapy against glomerulonephritis.

Immunological drivers of IgA nephropathy: Exploring the mucosa-kidney link

IgA nephropathy (IgAN) is the most common pattern of primary glomerular disease reported worldwide. Up to 40% of those with IgAN progress to end-stage kidney disease within 20 years of diagnosis, with no currently available disease-specific treatment. This is likely to change rapidly, with evolving insights into the mechanisms driving this disease. IgAN is an immune-complex-mediated disease, and its pathophysiology has been framed by the 'four-hit hypothesis', which necessitates four events to occur for clinically significant disease to develop. However, this hypothesis does not explain the wide variability observed in its presentation or clinical progression. Recently, there has been great interest in exploring the role of the mucosal immune system in IgAN, especially given the well-established link between mucosal infections and disease flares. Knowledge of antigen-mucosal interactions is now being successfully leveraged for therapeutic purposes; the gut-directed drug Nefecon (targeted release formulation-budesonide) is on track to become the first medication to be approved specifically for the treatment of IgAN. In this review, we examine established immunological paradigms in IgAN, explore how antigen-mucosal immune responses drive disease, and discuss how this knowledge is being used to develop new treatments.

The mucosal immune system and IgA nephropathy

The precise pathogenesis of immunoglobulin A nephropathy (IgAN) is still not clearly established but emerging evidence confirms a pivotal role for mucosal immunity. This review focuses on the key role of mucosa-associated lymphoid tissue (MALT) in promoting the onset of the disease, underlying the relationship among microbiota, genetic factors, food antigen, infections, and mucosal immune response. Finally, we evaluate potential therapies targeting microbes and mucosa hyperresponsiveness in IgAN patients.

LncRNA PTTG3P induced aberrant glycosylated IgA1 production and B cell growth in IgA nephropathy

Growing evidences suggested that lncRNAs played functional role in several cell functions such as cell growth, invasion, migration, metabolize, apoptosis, and differentiation. However, roles of lncRNA in the development and progression of IgAN remain unknown. In this reference, we indicated that PTTG3P level was overexpressed in IgAN samples compared to healthy subject. PTTG3P expression was also higher in urinary of IgAN cases than in urinary of healthy control. Furthermore, the urinary expression of PTTG3P was correlated with PTTG3P expression in intra-renal of IgAN cases. PTTG3P overexpression induced B cell growth and enhanced cyclin D1 and ki-67 expression. Overexpression of PTTG3P induced IL-1β and IL-8 production. miR-383 level was decreased in IgAN samples compared to healthy subject. In addition, miR-383 expression was also lower in urinary of IgAN cases than in urinary of healthy control. Elevated miR-383 expression decreased luciferase intensity regulated with PTTG3P, while overexpression of miR-383 had no effect on luciferase intensity of the mutant PTTG3P. PTTG3P overexpression suppressed miR-383 expression in B cells. Ectopic miR-383 expression suppressed B cell growth and IL-1β and IL-8 production. Finally, we showed that overexpression of PTTG3P promoted B cell growth and IL-1β and IL-8 production via regulating miR-383. There results proved that PTTG3P played crucial role in progression of IgAN.

New Insights into the Pathogenesis and Treatment Strategies in IgA Nephropathy

Background

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide. It is defined by mesangial IgA deposition, with consequent mesangial cell proliferation, inflammation, and tubulointerstitial fibrosis.

Summary

Approximately 30% of affected patients will progress to end-stage kidney disease within 20 years of diagnosis. Currently, there is no disease-specific treatment available and management recommendations are, in general, limited to optimization of lifestyle measures and use of renin-angiotensin-aldosterone system blockers. More recently, advances in the understanding of the pathogenesis of IgAN have informed the development of novel therapeutic strategies that are now being tested in clinical trials. These have focused on different areas that include modulating the production of poorly galactosylated IgA1, which is central to the development of IgAN, and inhibiting the downstream signaling pathways and complement activation that are triggered following mesangial IgA1 deposition. In this review, we will summarize important pathogenic mechanisms in IgAN and highlight important areas of interest where treatment strategies are being developed.

Key messages

IgAN is a common form of primary glomerulonephritis for which there is no current approved specific therapy. Recent advances in the understanding of its pathogenesis have led to the development of novel therapies, with the hope that new treatment options will be available soon to treat this condition.

An Update on Targeted Treatment of IgA Nephropathy: An Autoimmune Perspective

Immunoglobulin (Ig) A nephropathy (IgAN) is the commonest form of primary glomerulonephritis worldwide and is, considered a significant cause of end-stage renal disease in young adults. The precise pathogenesis of IgAN is unclear. The clinical and pathological features vary significantly between individuals and races, which makes treating IgAN difficult. Currently, the therapeutic strategies in IgAN are still optimal blood pressure control and proteinuria remission to improve the renal function in most cases. Immunosuppressive drugs such as corticosteroids can be considered in patients with persistent proteinuria and a high risk of renal function decline; however, they include a high toxicity profile. Therefore, the safety and selectivity of medications are critical concerns in the treatment of IgAN. Various pharmacological therapeutic targets have emerged based on the evolving understanding of the autoimmune pathogenesis of IgAN, which involves the immune response, mucosal immunity, renal inflammation, complement activation, and autophagy; treatments based on these mechanisms have been explored in preclinical and clinical studies. This review summarizes the progress concerning targeted therapeutic strategies and the relevant autoimmune pathogenesis in IgAN.

The number 13 of the family: a proliferation inducing ligand

The TNF superfamily member a proliferation inducing ligand (APRIL, TNFSF13) plays a late role in humoral immunity at the level of antibody-producing plasmocytes. The recent characterization of the first immunodeficient patient with an inactivating mutation in the APRIL gene provided the last piece of functional data lacking in the human system. Based on this function, APRIL has been considered as a valuable target to dampen unwanted antibody production. After reviewing the late data acquired on the physiological function of APRIL in humoral immunity, we will here review the state of the art regarding APRIL targeting in autoimmune diseases.

Are there animal models of IgA nephropathy?

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Up to 40% of IgAN patients develop end-stage kidney disease after 15-20 years. Despite the poor prognosis associated with this multifactorial disease, no clear treatment strategy has been identified, primarily due to the lack of understanding of its pathogenesis. Clinical observations indicate that aberrant IgAN immune systems, rather than intrinsic renal abnormalities, may be involved in its pathogenesis. Moreover, nephritogenic IgA and its related immune complexes are considered to be produced not only in the mucosa, but also in systemic immune sites, such as the bone marrow; however, there are numerous challenges to understanding this dynamic and complex immune axis in humans. Thus, several investigators have used experimental animal models. Although there are inter-strain differences in IgA molecules and immune responses between humans and rodents, animal models remain a powerful tool for investigating IgAN's pathogenesis, and the subsequent development of effective treatments. Here, we introduced some classical models of IgAN with or without genetic manipulation and recent translational approaches with some promising models. This includes humanized mouse models expressing human IgA1 and human IgA Fc receptor (CD89) that develops spontaneously the disease. Pre-clinical studies targeting IgA1 are discussed. Together, animal models are very useful tools to study pathophysiology and to validate new therapeutic approaches for IgAN.

An Update on the Current State of Management and Clinical Trials for IgA Nephropathy

IgA nephropathy remains the most common primary glomerular disease worldwide. It affects children and adults of all ages, and is a leading cause of end-stage kidney disease, making it a considerable public health issue in many countries. Despite being initially described over 50 years ago, there are still no disease specific treatments, with current management for most patients being focused on lifestyle measures and renin-angiotensin-aldosterone system blockade. However, significant advances in the understanding of its pathogenesis have been made particularly over the past decade, leading to great interest in developing new therapeutic strategies, and a significant rise in the number of interventional clinical trials being performed. In this review, we will summarise the current state of management of IgAN, and then describe major areas of interest where new therapies are at their most advanced stages of development, that include the gut mucosal immune system, B cell signalling, the complement system and non-immune modulators. Finally, we describe clinical trials that are taking place in each area and explore future directions for translational research.

The Phenotypic Difference of IgA Nephropathy and its Race/Gender-dependent Molecular Mechanisms

IgA nephropathy (IgAn), defined by the pre dominant de position of IgA in the glomerular mesangium, is the most common form of GN throughout the world. However, its incidence, sex distribution, clinical presentation, and progression and pathogenic initiating factors are largely variable and do not fit such a simple definition. To assess the heterogeneity of this disease, we recently conducted a clinical survey on the presentation and clinical management of patients with IgAn in Europe and Japan. This clinical survey highlights similarities and differences in patients from different cont inents. The survey revealed obvious differences between nations in the frequency of gastrointestinal complications, including inflammatory bowel diseases (IBD) and celiac disease, which were more frequent in European patients. Such findings are compatible with susceptibility loci related to intestinal immunity and IBD in recent genome wide association studies (GWAS) on IgAn. However, most of the molecules in these mucosal-related loci fulfill the immunologic function not only of gut-associated lymphoid tissue (GALT), but also nasopharyngeal/bronchial-associated lymphoid tissues (NALT/BALT). Indeed, a similar frequency of macrohematuria coinciding with upper respiratory infection, a hallmark manifestation of this disease, was found in the survey, emphasizing the pathogenic roles of these molecules in the NALT/BALT of patients with IgAn. Recent experimental and clinical studies including GWAS on multiple common infections and IBD indicate immune crosstalk between GALT and NALT/BALT, and some related mediators, such as TNF superfamily ligands (APRIL/BAFF). This review explains the epidemiologic heterogeneity of this disease with the clinical survey, and discusses race and sex-dependent molecular mechanisms.

Measurement of galactosyl-deficient IgA1 by the monoclonal antibody KM55 contributes to predicting patients with IgA nephropathy with high risk of long-term progression

BACKGROUND AND OBJECTIVE

About 25% of patients with IgA nephropathy (IgAN) progress to stage 5 chronic kidney disease (CKD) after years of evolution. Various tools have been developed in recent years designed to predict which of the patients will had poorer outcomes. The value of circulating galactosyl-deficient IgA1 (Gd-IgA1) has been related to a worse evolution of IgAN in several studies. There are also some publications that relate higher APRIL values with a worse evolution. Recently, a new method has been developed that allows measuring the value of circulating Gd-IgA1 in a simpler way than those previously available. The objective of this study is to analyze the influence of circulating Gd-IgA1, measured by this method, on the progression of IgAN.

MATERIALS AND METHODS

Forty-nine patients with a diagnosis of IgAN demonstrated by renal biopsy were selected in our center, without having received prior immunosuppressive treatment, for whom frozen serum was available. The median follow-up was 4 years. Gd-IgA1 was measured by lectin-independent ELISA with the monoclonal antibody KM55 (IgA1 kit Cat. No. 30111694. IBL Int., Hamburg, Germany). Likewise, APRIL levels were also measured in these patients.

RESULTS

19 (38.8%) patients reached stage 5 CKD. The fourth quartile of circulating Gd-IgA1 was related to a higher cumulative risk of reaching stage 5 CKD in the Kaplan-Meier analysis (risk at the 5th year 39.4% vs. 24.3%, log rank p=0.019). The Gd-IgA1 value was related to an increased risk of CKD stage 5 (HR 1.147, 95% CI 1.035-1.270, p=0.009), regardless of glomerular filtration rate, proteinuria, the percentage of sclerosed glomeruli and the value of segmental sclerosis. We did not find significant differences in the APRIL values.

CONCLUSIONS

The value of circulating Gd-IgA1 measured by the monoclonal antibody KM55 is related to a worse evolution of patients with IgAN independently of other variables, so it could be included in the study of patients to improve the prediction of the risk of disease progression.

[Measurement of galactosyl-deficient IgA1 by the monoclonal antibody KM55 contributes to predicting patients with IgA nephropathy with high risk of long-term progression]

BACKGROUND AND OBJECTIVE

About 25% of patients with IgA nephropathy (IgAN) progress to stage 5 chronic kidney disease (CKD) after years of evolution. Various tools have been developed in recent years designed to predict which of the patients will had poorer outcomes. The value of circulating galactosyl-deficient IgA1 (Gd-IgA1) has been related to a worse evolution of IgAN in several studies. There are also some publications that relate higher APRIL values with a worse evolution. Recently, a new method has been developed that allows measuring the value of circulating Gd-IgA1 in a simpler way than those previously available. The objective of this study is to analyze the influence of circulating Gd-IgA1, measured by this method, on the progression of IgAN.

MATERIALS AND METHODS

Forty-nine patients with a diagnosis of IgAN demonstrated by renal biopsy were selected in our center, without having received prior immunosuppressive treatment, for whom frozen serum was available. The median follow-up was 4 years. Gd-IgA1 was measured by lectin-independent ELISA with the monoclonal antibody KM55 (IgA1 kit Cat. No. 30111694. IBL Int., Hamburg, Germany). Likewise, APRIL levels were also measured in these patients.

RESULTS

19 (38.8%) patients reached stage 5 CKD. The fourth quartile of circulating Gd-IgA1 was related to a higher cumulative risk of reaching stage 5 CKD in the Kaplan-Meier analysis (risk at the 5th year 39.4% vs. 24.3%, log rank p=0.019). The Gd-IgA1 value was related to an increased risk of CKD stage 5 (HR 1.147, 95% CI 1.035-1.270, p=0.009), regardless of glomerular filtration rate, proteinuria, the percentage of sclerosed glomeruli and the value of segmental sclerosis. We did not find significant differences in the APRIL values.

CONCLUSIONS

The value of circulating Gd-IgA1 measured by the monoclonal antibody KM55 is related to a worse evolution of patients with IgAN independently of other variables, so it could be included in the study of patients to improve the prediction of the risk of disease progression.

New therapeutic perspectives for IgA nephropathy in children

Childhood IgA nephropathy (cIgAN) differs from the adult by having an abrupt clinical onset, often presenting as an acute attack that can progress to a chronic phase. No treatment guidelines have been established for the treatment of cIgAN. Given the severity of acute attack in children, and the number of life-years at stake, pediatricians prescribe immunosuppression in addition to renin-angiotensin system blockade. Non-specific immunosuppressors, such as corticosteroids, have systemic toxic effects, and given recent therapeutic advances in adult glomerulonephritis, new tailored strategies should be expected for children. The mucosal immune system has been highlighted as a key player in IgAN pathogenesis, and several biomarkers have been identified with a direct role in pathogenesis. In this review, we discuss current studies of conventional and novel therapeutic approaches for cIgAN.

Perspectives on how mucosal immune responses, infections and gut microbiome shape IgA nephropathy and future therapies

Infections have been considered to play a critical role in the pathogenesis of IgA nephropathy (IgAN) because synpharyngitic hematuria is a common feature in IgAN. However, how infections participate in this process is still debated. More recent studies have also revealed that the alteration of the gut microbiome exerts a profound effect on host immune responses, contributing to the etiology or progression of autoimmunity. Considering IgA as the first line of defense against bacterial and viral antigens, this review evaluates the relationships among intestinal infections, gut microbiome, and IgA for a better understanding of the pathogenesis of IgAN. Moreover, as a prototype of IgA immunity, we provide detailed clarification of IgAN pathogenesis to shed light on other diseases in which IgA plays a role. Finally, we discuss potential therapies focusing on microbes and mucosal immune responses in IgAN.

Crucial Role of AIM/CD5L in the Development of Glomerular Inflammation in IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) begins with aberrant IgA deposition in glomeruli, progresses to IgM/IgG/complement codeposition, and results in chronic inflammation and glomerular damage. However, the mechanism that drives such phlogogenic cascade has been unclear. Recently, apoptosis inhibitor of macrophage (AIM) protein was shown to modulate macrophages' function in various pathologic conditions, thereby profoundly affecting the progression of renal disorders, including AKI. A spontaneous IgAN model, grouped ddY (gddY) mouse, revealed the requirement of AIM for the overall inflammatory glomerular injury following IgA deposition.

METHODS

We established an AIM-deficient IgAN model (AIM ^-/- gddY) using CRISPR/Cas9 and compared its phenotype with that of wild-type gddY with or without recombinant AIM administration. An IgA-deficient IgAN model (IgA ^-/- gddY) was also generated to further determine the role of AIM.

RESULTS

In both human and murine IgAN, AIM colocalized with IgA/IgM/IgG in glomeruli, whereas control kidneys did not exhibit AIM deposition. Although AIM ^-/- gddY showed IgA deposition at levels comparable with those of wild-type gddY, they did not exhibit glomerular accumulation of IgM/IgG complements, CD45⁺ leukocyte infiltration, and upregulation of inflammatory/fibrogenic genes, indicating protection from glomerular lesions and proteinuria/hematuria. Recombinant AIM administration reconstituted the IgAN phenotype, resulting in IgM/IgG/complement IgA codeposition. Neither spontaneous IgM/IgG codeposition nor disease was observed in IgA ^-/- gddY mice.

CONCLUSIONS

AIM may contribute to stable immune complex formation in glomeruli, thereby facilitating IgAN progression. Therefore, AIM deposition blockage or disassociation from IgM/IgG may present a new therapeutic target on the basis of its role in IgAN inflammation initiation.

Integrated GWAS and mRNA Microarray Analysis Identified IFNG and CD40L as the Central Upstream Regulators in Primary Biliary Cholangitis

Genome‐wide association studies (GWASs) in European and East Asian populations have identified more than 40 disease‐susceptibility genes in primary biliary cholangitis (PBC). The aim of this study is to computationally identify disease pathways, upstream regulators, and therapeutic targets in PBC through integrated GWAS and messenger RNA (mRNA) microarray analysis. Disease pathways and upstream regulators were analyzed with ingenuity pathway analysis in data set 1 for GWASs (1,920 patients with PBC and 1,770 controls), which included 261 annotated genes derived from 6,760 single‐nucleotide polymorphisms (P < 0.00001), and data set 2 for mRNA microarray analysis of liver biopsy specimens (36 patients with PBC and 5 normal controls), which included 1,574 genes with fold change >2 versus controls (P < 0.05). Hierarchical cluster analysis and categorization of cell type–specific genes were performed for data set 2. There were 27 genes, 10 pathways, and 149 upstream regulators that overlapped between data sets 1 and 2. All 10 pathways were immune‐related. The most significant common upstream regulators associated with PBC disease susceptibility identified were interferon‐gamma (IFNG) and CD40 ligand (CD40L). Hierarchical cluster analysis of data set 2 revealed two distinct groups of patients with PBC by disease activity. The most significant upstream regulators associated with disease activity were IFNG and CD40L. Several molecules expressed in B cells, T cells, Kupffer cells, and natural killer–like cells were identified as potential therapeutic targets in PBC with reference to a recently reported list of cell type–specific gene expression in the liver. Conclusion: Our integrated analysis using GWAS and mRNA microarray data sets predicted that IFNG and CD40L are the central upstream regulators in both disease susceptibility and activity of PBC and identified potential downstream therapeutic targets.

TLR9 activation induces aberrant IgA glycosylation via APRIL- and IL-6-mediated pathways in IgA nephropathy

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of IgA nephropathy (IgAN). However, the pathogenic mechanisms driving Gd-IgA1 production have not been fully elucidated. Innate-immune activation via Toll-like receptor 9 (TLR9) is known to be involved in Gd-IgA1 production. A proliferation inducing ligand (APRIL) and IL-6 are also known to enhance Gd-IgA1 synthesis in IgAN. With this as background, we investigated how TLR9 activation in IgA secreting cells results in overproduction of nephritogenic IgA in the IgAN-prone ddY mouse and in human IgA1-secreting cells. Injection of the TLR9 ligand CpG-oligonucleotides increased production of aberrantly glycosylated IgA and IgG-IgA immune complexes in ddY mice that, in turn, exacerbated kidney injury. CpG-oligonucleotide-stimulated mice had elevated serum levels of APRIL that correlated with those of aberrantly glycosylated IgA and IgG-IgA immune complexes. In vitro, TLR9 activation enhanced production of the nephritogenic IgA as well as APRIL and IL-6 in splenocytes of ddY mice and in human IgA1-secreting cells. However, siRNA knock-down of APRIL completely suppressed overproduction of Gd-IgA1 induced by IL-6. Neutralization of IL-6 decreased CpG-oligonucleotide-induced overproduction of Gd-IgA1. Furthermore, APRIL and IL-6 pathways each independently mediated TLR9-induced overproduction of Gd-IgA1. Thus, TLR9 activation enhanced synthesis of aberrantly glycosylated IgA that, in a mouse model of IgAN, further enhanced kidney injury. Hence, APRIL and IL-6 synergistically, as well as independently, enhance synthesis of Gd-IgA1.