Complement blockade in ANCA-associated vasculitis: an index case, current concepts and future perspectives

Complement as a major mediator of ANCA vasculitis and a target for precision therapy

INTRODUCTION

Complement was long thought not to be involved in ANCA vasculitis pathogenesis until studies in murine models demonstrated its central role. The current theory is ANCA-activated neutrophils degranulate and release factors that activate complement, which, in turn, recruits more neutrophils and causes an inflammatory amplification loop that results in the vascular inflammation characteristic of disease. Targeting this amplification loop through complement inhibition has proven to be effective in ANCA vasculitis treatment.

AREAS COVERED

A PubMed search was conducted using key terms 'ANCA vasculitis' AND 'complement system.' We review findings from experimental mouse models, in vitro studies, and human ANCA vasculitis that support a role for complement activation in disease pathogenesis. We also summarize results from pivotal clinical studies demonstrating the safety and efficacy of complement inhibition in ANCA vasculitis treatment.

EXPERT OPINION

While complement activation is undoubtedly involved in ANCA vasculitis pathogenesis, less clear is whether measuring complement activation markers can reliably assess disease activity, predict those who will benefit from complement-targeting therapy, or identify patients in stable remission and able to stop therapy. Better understanding the clinical implications of complement activation will shed more light on the utility of complement inhibition and facilitate precision medicine in ANCA vasculitis.

Superiority of Avacopan and Mepolizumab to Glucocorticoid Tapering in the Treatment of Anti-neutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis: A Systematic Review

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) comprises a spectrum of autoimmune diseases, including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Studies have shown that avacopan and mepolizumab are promising therapeutics for partial or complete replacement of glucocorticoids (GC), with sustained remission while completely weaning off GC. Avacopan inhibits C5aR in the complement pathway, preventing neutrophil migration, while mepolizumab targets IL-5R, reducing eosinophil activity. Additionally, complement inhibition has not only contributed to the recovery of renal function and alleviation of physical symptoms but has also enhanced patients' overall quality of life and mental well-being. This systematic review explores the pathogenesis of AAV, traditional treatments, and the potential of emerging complement and interleukin antagonist therapies such as avacopan and mepolizumab in revolutionizing AAV management.

Treatment strategies for ANCA-associated vasculitides: from standard protocols to future horizons

INTRODUCTION

ANCA-associated vasculitides (AAV), classified into granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis represent a group of disorders characterized by necrotizing vasculitis of small vessels, endothelial injury and tissue damage. The outcomes and prognosis of AAV have undergone significant changes with the introduction of glucocorticoids (GCs) and other immunosuppressants (cyclophosphamide, azathioprine, methotrexate, and mycophenolate mofetil). The enhanced understanding of pathogenesis has subsequently led to the incorporation into clinical practice of drugs targeting specific therapeutic targets.

AREAS COVERED

After an extensive literature search of Pubmed, Medline, Embase of the most recent evidence, we provide an overview of available treatments, highlighting how newer drugs have integrated into standard protocols. Our review also explores potential new therapeutic targets, including B cell depletion and inhibition, T cell inhibition, complement inhibition, and IL-5 and IgE inhibition.

EXPERT OPINION

There is hope that the new treatment targets currently under study in AAV may enable a faster and more lasting clinical response, ensuring the reduction of possible side effects from therapies. Moreover, numerous aspects necessitate further exploration in the future, such as tailoring of GCs, integration of GCs-sparing agents, efficacy of combination therapy, optimal maintenance therapy, to reduce organ-damage and improve quality of life.

Evolution of Therapy for ANCA-Associated Vasculitis with Kidney Involvement

ANCA-associated vasculitis (AAV) belongs to a group of small vessel systemic vasculitides characterized by granulomatous and neutrophilic inflammation of various tissues. Patients often have circulating autoantibodies targeting neutrophilic antigens. Although AAV was once associated with severe end-organ damage and extremely high mortality rates, the use of glucocorticoids and cyclophosphamide led to a paradigm change in its treatment. Over the past 20 years, significant progress in understanding the immunopathogenesis of AAV has enabled development of targeted immunotherapies, providing a much better prognosis for patients. This review describes the evolution of treatment of AAV, particularly for patients with kidney involvement.

New Insights into Pathogenesis and Treatment of ANCA-Associated Vasculitis: Autoantibodies and Beyond

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a group of rare systemic diseases affecting small-caliber vessels. The damage caused by AAV mainly involves the lung and kidneys. AAV includes three different types: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Although the different phenotypic forms of AAV share common features, recent studies have shown that there are significant differences in terms of pathogenetic mechanisms involving both the adaptive and innate immune systems. Advances in our understanding of pathogenesis have enabled the development of immuno-targeted therapies. This review illustrates the characteristics of the various forms of AAV and the new therapies available for this disease that can have lethal consequences if left untreated.

The complement system in antineutrophil cytoplasmic antibody-associated vasculitis: pathogenic player and therapeutic target

PURPOSE OF REVIEW

The purpose of this review is to discuss the role of the complement system in the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) as well as the employment of complement inhibitors in AAV treatment.

RECENT FINDINGS

AAV has traditionally been considered a pauci-immune disease until recent findings demonstrated the pathogenic role of the complement system. The complement alternative pathway is crucial in AAV, and C5a seems to be a key molecule for AAV to develop. Avacopan, a C5a-receptor (C5aR) antagonist, proved effective in achieving AAV remission and ameliorating kidney function.

SUMMARY

The increased circulating levels of some complement components - as well as the consumption of others - in patients with AAV suggested a systemic activation of the complement system. Low C3 levels correlate with a more aggressive disease and a worse renal prognosis. In ANCA-associated glomerulonephritis, renal deposits of C3d and properdin, suggestive of local alternative pathway activation, correlate with glomerular crescents and proteinuria. The interaction between C5a and neutrophil triggers alternative pathway activation, suggesting the central role of C5a in AAV pathogenesis. Avacopan, a C5aR inhibitor, showed beneficial effects in AAV and represents a promising therapy to achieve sustained remission and to spare glucocorticoids.

Complement Inhibition in ANCA-Associated Vasculitis

Efficacy of immunosuppressive treatment of Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is complicated by its toxicity. With the replacement of cyclophosphamide with rituximab, serious adverse events seem to be associated especially with high-dose corticosteroids. Activation of alternative complement pathway plays an important role in the pathogenesis of AAV. Avacopan (C5a receptor inhibitor) was demonstrated to have at least similar efficacy and better safety (in terms of corticosteroid-related adverse events) compared with high-dose corticosteroids in the induction treatment of AAV. Other modes of the inhibition of alternative complement pathway are currently tested in AAV or could be considered on the basis of the experience in other glomerular diseases.

Hypocomplementemia is associated with more severe renal disease and worse renal outcomes in patients with ANCA-associated vasculitis: a retrospective cohort study

Background

The complement system has been recently proposed to play an important role in the pathogenesis of ANCA-associated vasculitis (AAV). This study evaluated the value of serum and kidney deposited C3 in predicting renal outcomes in AAV.

Methods

This was a retrospective study of 47 patients with AAV, who were categorized according to their serum C3 levels as hypo- or normo-complementemic and to those with positive or negative kidney biopsy immunofluorescence (IF) for C3. Baseline characteristics as well as progression to end-stage renal disease (ESRD) between the 2 groups were compared.

Results

In total, 23% (11/47) were hypo-complementemic; these patients were older (74 vs. 65 years, p = 0.013), had higher creatinine levels (4.9 vs. 2.2 mg/dL, p = 0.006), were more often hemodialysis dependent (64% vs. 19%, p = 0.009) and progressed more often to ESRD (55% vs. 11%, p = 0.01) compared to normo-complementemic patients (n = 36). On multivariate analysis, serum creatinine at diagnosis (HR = 16.8, 95%CI: 1.354–208.62, p = 0.028) and low serum C3 (HR = 2.492; 95% CI: 1.537–11.567; p = 0.044) were independent predictors for ESRD. Among 25 patients with an available kidney biopsy, 56% had C3 deposition by IF and displayed more often a mixed histological pattern (72% vs. 27%, p = 0.033), low serum C3 levels (42% vs. 18%, p < 0.001) and serious infections during follow-up (57% vs. 18%, p = 0.047) compared to those with negative (n = 11) IF staining.

Conclusion

Almost one of four patients with AAV has low C3 levels at diagnosis which is associated with more severe renal disease and worse renal outcomes (ESRD). This should be taken into account in therapeutic and monitoring strategies.

Long-term use and remission of granulomatosis with polyangiitis with the oral C5a receptor inhibitor avacopan

Granulomatosis with polyangiitis (GPA) is a rare antineutrophil cytoplasm antibody-associated vasculitis. Several therapeutic advances have occurred over the past two decades, but relapse rate remains high and refractory cases are not uncommon. Here, we present the case of a female patient diagnosed with GPA at the age of 9 years with a severe, multirelapsing disease course which failed to adequately respond to conventional therapies. Avacopan, a novel C5a receptor inhibitor, was started based on phase II studies that showed promise as a steroid-sparing adjunct. The patient was able to successfully reduce her glucocorticoid dose and reduce her immunosuppressive treatments without another flare. She has been on avacopan for 35 months, had no adverse events that required its discontinuation, and her disease is in sustained remission.

The rise of complement in ANCA-associated vasculitis: from marginal player to target of modern therapy

The complement system plays a central role in autoimmune diseases, including anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Although complement deposition is scarce in AAV pathological samples, complement activation is required for the development of necrotizing crescentic glomerulonephritis (NCGN) in mouse models of AAV and occurs via the alternative pathway. The anaphylatoxin C5a, produced by the final complement pathway, is determinant to drive the disease in animal models. C5a primes human neutrophils and enhances their activation induced by ANCA; activated neutrophils, in turn, release factors that lead to C5a generation, establishing a self-amplifying loop. C5a is also significantly increased in the serum of AAV patients with active disease compared to those in remission or healthy controls. Inhibition of the C5a receptor with avacopan is an emerging therapy that will probably allow AAV treatment with glucocorticoid-free regimens.

The role of complement in antineutrophil cytoplasmic antibody-associated vasculitis

PURPOSE OF REVIEW

To provide a comprehensive overview of the current insight into the role of complement activation in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). In addition, the therapeutic options targeting the complement system in AAV are discussed.

RECENT FINDINGS

It has become increasingly clear that complement, and more specifically signalling through the C5a receptor, contributes to the immunopathology of AAV. This has led to the design of clinical trials with a C5a receptor blocker. The first results show a reduction in tissue damage and a favourable safety profile, as other parts of the complement defence system are left intact.

SUMMARY

Although AAV was initially regarded as a pauci-immune disease, it is now well established that, in addition to autoantibodies, complement plays an essential role in the disease process. Animal models delivered the first insight, but the effective therapeutic interventions using complement inhibitors provided the proof that indeed complement activation contributes to disease activity and tissue damage in human AAV.

Complement inhibition in ANCA vasculitis

A role for the alternative complement pathway has emerged in the understanding of ANCA vasculitis pathogenesis. Current therapies of ANCA vasculitis are limited by partial efficacy and toxicity and many patients pursue a relapsing course. Improved therapies are needed. Inhibition of the alternative complement pathway component C5a is attractive due to its role in neutrophil activation and migration, and engagement of other inflammatory and thrombotic mechanisms. Two inhibitors of C5a are in clinical development for ANCA vasculitis: avacopan, an oral C5a receptor inhibitor has demonstrated efficacy, safety and steroid sparing in two Phase II trials; and IFX-1, a monoclonal antibody to C5a which is entering Phase II development. Complement inhibition has the potential to contribute to remission induction protocols achieving a higher quality of remission as well as replacing steroids. Confirmation of safety, especially infective risk, and the potential to replace steroids depends on further studies and a role in relapse prevention needs to be explored.

Increased renal damage in hypocomplementemic patients with ANCA-associated vasculitis: retrospective cohort study

INTRODUCTION

The complement system has an important role in the pathogenesis of vasculitis associated with antineutrophilic cytoplasmic antibody (AAV) mainly at the level of the kidneys because patients with complement deposits on the glomerular basal membrane present more aggressive disease compared with those with pauci-immune vasculitis.

AIM

To analyze the association of hypocomplementemia with the clinical manifestations, laboratory data, renal histology, progress to renal insufficiency, and mortality of patients with AAV.

METHODS

Retrospective cohort study (2000-2007) included 93 patients with AAV. Hypocomplementemia is defined as having C3 values lower than 80 mg/dL or C4 values below 15 mg/dL. Demographic, statistical, clinical, hematological, serological, and histopathological characteristics of all the patients with and without diagnosis of hypocomplementemia were compared. In order to evaluate variable independence, a logistic regression analysis was used.

RESULTS

Ninety-three patients were studied of whom 63 (67.7%) had complement dosage at the moment of AAV diagnosis. Seven patients (11.1%) presented hypocomplementemia and a greater kidney involvement compared with normocomplementemic patients. Thirty renal biopsies were analyzed and 4 (13.3%) showed immunocomplex (IC) or complement deposits by an immunofluorescence test (IFT). Patients with "non-pauci-immune" AAV also presented terminal chronic renal disease (TCRD).

CONCLUSION

There is an association between low complement and the degree of renal damage in patients with AAV. Patients with renal biopsies confirming IC and/or complement deposits showed more aggressive renal disease. Key Points • The complement system has an important role in the pathogenesis of vasculitis associated to antineutrophilic cytoplasmic antibody. • The studies in murine models confirming the complement activation by alternative pathway and particularly the receptor C5a (C5aR) is necessary for the development of glomerulonefritis. • Complement deposit observed in the renal biopsies of patients diagnosed with AAV was correlated to greater kidney damage, greater proteinuria and major disease activity compared to patients diagnosed with typical pauci-immune vasculitis. • The presence of hypocomplementemia at the onset of the disease was also associated with a greater organ involvement, poor prognosis and greater mortality.

A rare case of Alport syndrome, atypical hemolytic uremic syndrome and Pauci-immune crescentic glomerulonephritis

Background

Renal thrombotic microangiopathy (TMA) is occasionally seen in biopsies with pauci-immune necrotizing crescentic glomerulonephritis (PCGN). Recent study indicated that the complement activation is more prominent in the ANCA-negative glomerulonephritis.

Case presentation

We report a case of concurrent TMA and PCGN without ANCA positivity. Interestingly, our patient also had biopsy features supportive of Alport syndrome (AS). Genetic studies identified variants and polymorphisms in alternative complement pathway genes that confer substantial risk of developing atypical hemolytic uremic syndrome (aHUS).

Conclusions

Abnormal activation in complement pathway may represent a common pathogenic link between these three distinct entities.

Clinical Implications of Excessive Neutrophil Extracellular Trap Formation in Renal Autoimmune Diseases

Neutrophil extracellular traps (NETs) are extracellular DNA structures covered with antimicrobial peptides, danger molecules, and autoantigens that can be released by neutrophils. NETs are an important first-line defense mechanism against bacterial, viral, fungal, and parasitic infections, but they can also play a role in autoimmune diseases. NETs are immunogenic and toxic structures that are recognized by the autoantibodies of patients with antineutrophil cytoplasmic antibodies−associated vasculitis (AAV) (i.e., against myeloperoxidase or proteinase-3) and systemic lupus erythematosus (SLE) (i.e., against double-stranded DNA, histones, or nucleosomes). There is cumulating preclinical and clinical evidence that both excessive formation and impaired degradation of NETs are involved in the pathophysiology of AAV and SLE. These autoimmune diseases give rise to 2 clinically and pathologically distinct forms of glomerulonephritis (GN), respectively, crescentic pauci-immune GN and immune complex−mediated GN. Therefore, it is relevant to understand the different roles NET formation can play in the pathophysiology of these most prevalent renal autoimmune diseases. This review summarizes the current concepts on the role of NET formation in the pathophysiology of AAV and SLE, and provides a translational perspective on the clinical implications of NETs, such as potential therapeutic approaches that target NET formation in these renal autoimmune diseases.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Recent advances in understanding of the pathogenesis of ANCA-associated vasculitis

Anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) are rare systemic autoimmune diseases characterised by inflammation of small blood vessels. Recent developments have been made in our understanding of the pathogenesis of these diseases, including the pathogenic role of ANCA, neutrophils and monocytes as mediators of injury, dysregulation of the complement system, and the role of T and B cells. Current treatment strategies for AAV are based on broad immunosuppression, which may have significant side effects. Advances in understanding of the pathogenesis of disease have led to the identification of new therapeutic targets which may lead to treatment protocols with less-toxic side effects. The aim of this review is to summarise current information and recent advances in understanding of the pathogenesis of AAV.

Glucocorticoids in the Treatment of Glomerular Diseases: Pitfalls and Pearls

Glucocorticoids exert anti-inflammatory and immunosuppressive activities by genomic and nongenomic effects. The classic genomic effects are mediated by cytosolic glucocorticoid receptors that can upregulate the expression of anti-inflammatory proteins in the nucleus (transactivation) or repress the translocation of proinflammatory transcription factors from the cytosol into the nucleus (transrepression). The nongenomic effects are probably mediated by membrane glucocorticoid receptors. Glucocorticoid receptors are expressed also in podocytes and experimental data suggest that glucocorticoids may protect from podocyte injury. Glucocorticoids have a low therapeutic index and may exert a number of time-dependent and dose-dependent side effects. Measures to prevent or attenuate side effects include single-morning administration of short-acting glucocorticoids, dietetic counseling, increasing physical activity, frequent monitoring, and adapting the doses to the clinical conditions of the patient. Synthetic glucocorticoids, either given alone or in combination with other immunosuppressive drugs, are still the cornerstone therapy in multiple glomerular disorders. However, glucocorticoids are of little benefit in C3 glomerulopathy and may be potentially deleterious in patients with maladaptive focal glomerulosclerosis. Their efficacy depends not only on the type and severity of glomerular disease, but also on the timeliness of administration, the dosage, and the duration of treatment. Whereas an excessive use of glucocorticoids can be responsible for severe toxicity, too low a dosage and too short duration of glucocorticoid treatment can result in false steroid resistance.

Hypocomplementemia is associated with worse renal survival in ANCA-positive granulomatosis with polyangiitis and microscopic polyangiitis

Recent data suggest the existence of a complement alternative pathway activation in the pathogenesis of antineutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV), a condition that remains poorly understood. This study aims to assess the clinical characteristics and outcomes of granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) patients with regard to their plasma complement levels at diagnosis. A retrospective monocentric study carried out at Caen University Hospital led to the identification of proteinase-3- or myeloperoxidase-ANCA-positive GPA and MPA patients from January 2000 to June 2016 and from September 2011 to June 2016, respectively. All patients with available C3 and C4 levels at diagnosis were included. Patients were categorized in the hypocomplementemia group if their C3 and/or C4 levels at diagnosis were below the lower limit of the normal range. Among the 76 AAV patients (43 GPA, 33 MPA), 4 (5%) had hypocomplementemia, and the 72 remaining patients exhibited normal plasma complement levels. All 4 hypocomplementemia patients had renal involvement. Hypocomplementemia was followed in 1 patient whose post-treatment complement level normalized within 1 month. Among all clinical and ANCA specificity, including relapse-free survival (p = 0.093), only overall and renal survival rates were significantly lower in the hypocomplementemia group (p = 0.0011 and p<0.001, respectively). Hypocomplementemia with low C3 and/or C4 levels at GPA or MPA diagnosis may be responsible for worse survival and renal prognosis. These results argue for larger and prospective studies to better determine the epidemiology of the disease and to assess complement-targeting therapy in these patients.

Primary Vasculitis in Childhood: GPA and MPA in Childhood

Childhood onset anti-neutrophilic cytoplasmic antibody (ANCA) associated vasculitis (AAV) is a rare group of primary systemic vasculitides affecting medium and small blood vessels. AAV includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA), and renal limited ANCA vasculitis. These disorders are associated with severe clinical manifestations, frequent relapses and a high cumulative morbidity, and often present with multisystem involvement. Renal involvement is common in the pediatric age group, characterized by pauci-immune necrotizing and crescentic glomerulonephritis which frequently progresses to chronic kidney disease in adulthood. ANCAs against proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO) (MPO-ANCA) remain the hallmark of AAV and are integral to the disease pathogenesis. Newer understanding of neutrophil extracellular traps and complement activation have provided better insights into disease pathogenesis. A pediatric vasculitis working group has developed and validated childhood vasculitis classification criteria and disease activity and damage scores. No specific pediatric treatment recommendations exist due to rare nature of the illness in pediatric population. Smaller case series have been published on the efficacy of adult treatment regimens in pediatric patients. The prognosis often remains guarded with frequent relapses and a high cumulative morbidity. The aim of this article is to provide a comprehensive review on pediatric AAV with a focus on recent observations regarding epidemiology, disease pathogenesis, treatment, and prognosis.

Efficacy of eculizumab in an adult patient with HIV-associated hemolytic uremic syndrome: A case report

INTRODUCTION

Hemolytic uremic syndrome (HUS) in Human Immunodeficiency Virus (HIV)-positive patients has become a rare cause of kidney injury since the era of highly active antiretroviral therapy (HAART). Plasma exchange and antiretroviral therapy were previously recommended but often failed to achieve remission. We report a case of HUS in a HIV-positive patient treated successfully with eculizumab.

CASE SUMMARY

A 52-year-old woman presented to hospital with acute renal failure, thrombocytopenia, anemia, and hypoxemia. She had been diagnosed with HIV infection in 1997. Kidney biopsy showed several fibrinous microthrombi in the glomerular capillaries, formation of thrombi in arterioles, moderate parietal and mesangial deposits of C3 and Immunoglobulin M, and intense glomerular and arterial deposits of Complement component 5b9 complement component. Serum HIV viral load was 227,848 copies/mL, and CD4 lymphocyte count was 120 cells/μL. A diagnosis of HIV-associated HUS was made. The patient had no confounding cause of HUS. Initiation of eculizumab and HAART resulted in complete hematological remission on day 32 and dialysis withdrawal on day 110. The patient has not relapsed during long-term follow-up (M17).

CONCLUSION

This observation suggests that eculizumab can achieve remission in HIV patients with HUS.