C3 glomerulopathy and eculizumab: a report on four paediatric cases

Recurrent C3 glomerulopathy after kidney transplantation

The complement system is part of innate immunity and is pivotal in protecting the body against pathogens and maintaining host homeostasis. Activation of the complement system is triggered through multiple pathways, including antibody deposition, a mannan-binding lectin, or activated complement deposition. C3 glomerulopathy (C3G) is a rare glomerular disease driven by complement dysregulation with high post-transplantation recurrence rates. Its treatment is mainly based on immunosuppressive therapies, specifically mycophenolate mofetil and glucocorticoids. Recent years have seen significant progress in understanding complement biology and its role in C3G pathophysiology. New complement-tergeting treatments have been developed and initial trials have shown promising results. However, challenges persist in C3G, with recurrent post-transplantation cases leading to suboptimal outcomes. This review discusses the pathophysiology and management of C3G, with a focus on its recurrence after kidney transplantation.

Eculizumab as a treatment for C3 glomerulopathy: a single-center retrospective study

BACKGROUND

C3 Glomerulopathy (C3G) is a rare glomerular disease caused by dysregulation of the complement pathway. Based on its pathophysiology, treatment with the monoclonal antibody eculizumab targeting complement C5 may be a therapeutic option. Due to the rarity of the disease, observational data on the clinical response to eculizumab treatment is scarce.

METHODS

Fourteen patients (8 female, 57%) treated for C3 glomerulopathy at the medical center of the University of Freiburg between 2013 and 2022 were included. Subjects underwent biopsy before enrollment. Histopathology, clinical data, and response to eculizumab treatment were analyzed. Key parameters to determine the primary outcome were changes of estimated glomerular filtration rate (eGFR) over time. Positive outcome was defined as > 30% increase, stable outcome as ±30%, negative outcome as decrease > 30% of eGFR.

RESULTS

Eleven patients (78.8%) were treated with eculizumab, three received standard of care (SoC, 27.2%). Median follow-up time was 68 months (IQR: 45-98 months). Median eculizumab treatment duration was 10 months (IQR 5-46 months). After eculizumab treatment, five patients showed a stable outcome, six patients showed a negative outcome. Among patients receiving SoC, one patient showed a stable outcome, two patients showed a negative outcome.

CONCLUSIONS

The benefit of eculizumab in chronic progressive C3 glomerulopathy is limited.

Spectrum of Kidney Injury Following COVID-19 Disease: Renal Biopsy Findings in a Single Italian Pathology Service

The onset of coronavirus disease (COVID-19) as a pandemic infection, has led to increasing insights on its pathophysiology and clinical features being revealed, such as a noticeable kidney involvement. In this study, we describe the histopathological, immunofluorescence, and ultrastructural features of biopsy-proven kidney injury observed in a series of SARS-CoV-2 positive cases in our institution from April 2020 to November 2021. We retrieved and retrospectively reviewed nine cases (two pediatric and seven adults) that experienced nephrotic syndrome (six cases), acute kidney injury (two cases), and a clinically silent microhematuria and leukocyturia. Kidney biopsies were investigated by means of light microscopy, direct immunofluorescence, and electron microscopy. The primary diagnoses were minimal change disease (four cases), acute tubular necrosis (two cases), collapsing glomerulopathy (two cases), and C3 glomerulopathy (one case). None of the cases showed viral or viral-like particles on ultrastructural analysis. Novel and specific histologic features on kidney biopsy related to SARS-CoV-2 infection have been gradually disclosed and reported, harboring relevant clinical and therapeutic implications. Recognizing and properly diagnosing renal involvement in patients experiencing COVID-19 could be challenging (due to the lack of direct proof of viral infection, e.g., viral particles) and requires a proper integration of clinical and pathological data.

Long-term follow-up including extensive complement analysis of a pediatric C3 glomerulopathy cohort

BACKGROUND

C3 glomerulopathy (C3G) is a rare kidney disorder characterized by predominant glomerular depositions of complement C3. C3G can be subdivided into dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). This study describes the long-term follow-up with extensive complement analysis of 29 Dutch children with C3G.

METHODS

Twenty-nine C3G patients (19 DDD, 10 C3GN) diagnosed between 1992 and 2014 were included. Clinical and laboratory findings were collected at presentation and during follow-up. Specialized assays were used to detect rare variants in complement genes and measure complement-directed autoantibodies and biomarkers in blood.

RESULTS

DDD patients presented with lower estimated glomerular filtration rate (eGFR). C3 nephritic factors (C3NeFs) were detected in 20 patients and remained detectable over time despite immunosuppressive treatment. At presentation, low serum C3 levels were detected in 84% of all patients. During follow-up, in about 50% of patients, all of them C3NeF-positive, C3 levels remained low. Linear mixed model analysis showed that C3GN patients had higher soluble C5b-9 (sC5b-9) and lower properdin levels compared to DDD patients. With a median follow-up of 52 months, an overall benign outcome was observed with only six patients with eGFR below 90 ml/min/1.73 m² at last follow-up.

CONCLUSIONS

We extensively described clinical and laboratory findings including complement features of an exclusively pediatric C3G cohort. Outcome was relatively benign, persistent low C3 correlated with C3NeF presence, and C3GN was associated with higher sC5b-9 and lower properdin levels. Prospective studies are needed to further elucidate the pathogenic mechanisms underlying C3G and guide personalized medicine with complement therapeutics.

Myeloperoxidase immunohistochemical staining can identify glomerular endothelial cell injury in dense deposit disease

BACKGROUND

Previous studies have demonstrated residual complement-mediated deposits in repeat kidney biopsies of C3 glomerulopathies (C3G) (dense deposit disease (DDD) and C3 glomerulonephritis) following eculizumab treatment, despite some clinical improvement. With residual complement deposition, it is difficult to determine whether there is a reduced complement-mediated endothelial cell injury. We validated that myeloperoxidase (MPO) immunohistochemical staining identified glomerular endothelial cell injury in crescentic glomerulonephritis and C3G.

CASE (DIAGNOSIS/TREATMENT)

We report that MPO staining in the glomerular endothelium of the post-treatment kidney biopsy was significantly reduced after 3 years of eculizumab treatment and clinical improvement in a 5-year-old boy with initial DDD and secondary crescent formation.

CONCLUSION

We find that immunostaining for MPO is a useful method to compare glomerular endothelial injury in C3G following eculizumab treatment. This finding also supports the notion that eculizumab, a C5 blocker, may not mainly block C3 deposits in the glomeruli but significantly blocks final activation of the complement cascade, thus reducing glomerular endothelial cell injury.

Mycoplasma pneumoniae Infection Associated C3 Glomerulopathy Presenting as Severe Crescentic Glomerulonephritis

C3 glomerulopathy (C3GP) is a group of diseases caused by a deregulated complement system, which encompasses both dense deposit disease and C3 glomerulonephritis. Renal manifestations of C3GP are primarily of proliferative glomerulonephritis, and only a few case reports of crescentic glomerulonephritis (CGN) in association with C3GP are available. Here is a case of an adult South-Asian female, who was diagnosed as seropositive acute Mycoplasma pneumoniae infection, with associated systemic manifestations, including immune-type extravascular haemolysis and nephrotic range proteinuria. Subsequent renal biopsy revealed CGN with disrupted Bowman's capsules and necrotizing lesions. Immunofluorescence showed coarse granular mesangial C3 deposits with negative IgM, IgG, IgA, and C1q. The immunomorphological phenotype raised two possibilities including C3GP and infection-related glomerulonephritis (IRGN). Persistent proteinuria with no evidence of resolution even after 6 months of follow-up favoured C3GP over IRGN. The patient proceeded to end-stage renal failure requiring renal replacement despite aggressive immunosuppression. This case illustrates the rare association of CGN with C3GP induced by Mycoplasma pneumoniae infection, highlighting the importance of correct diagnosis as well as timely identification of triggering factors in CGN on patient outcome.

Eculizumab exposure in children and young adults: indications, practice patterns, and outcomes-a Pediatric Nephrology Research Consortium study

BACKGROUND

Eculizumab is approved for the treatment of atypical hemolytic uremic syndrome (aHUS). Its use off-label is frequently reported. The aim of this study was to describe the broader use and outcomes of a cohort of pediatric patients exposed to eculizumab.

METHODS

A retrospective, cohort analysis was performed on the clinical and biomarker characteristics of eculizumab-exposed patients < 25 years of age seen across 21 centers of the Pediatric Nephrology Research Consortium. Patients were included if they received at least one dose of eculizumab between 2008 and 2015. Traditional summary statistics were applied to demographic and clinical data.

RESULTS

A total of 152 patients were identified, mean age 9.1 (+/-6.8) years. Eculizumab was used "off-label" in 44% of cases. The most common diagnoses were aHUS (47.4%), Shiga toxin-producing Escherichia coli HUS (12%), unspecified thrombotic microangiopathies (9%), and glomerulonephritis (9%). Genetic testing was available for 60% of patients; 20% had gene variants. Dosing regimens were variable. Kidney outcomes tended to vary according to diagnosis. Infectious adverse events were the most common adverse event (33.5%). No cases of meningitis were reported. Nine patients died of noninfectious causes while on therapy.

CONCLUSIONS

This multi-center retrospective cohort analysis indicates that a significant number of children and young adults are being exposed to C5 blockade for off-label indications. Dosing schedules were highly variable, limiting outcome conclusions. Attributable adverse events appeared to be low. Cohort mortality (6.6%) was not insignificant. Prospective studies in homogenous disease cohorts are needed to support the role of C5 blockade in kidney outcomes.

Recurrent glomerulonephritis after kidney transplantation: a practical approach

PURPOSE OF REVIEW

This review will provide a practical approach in the assessment of kidney failure patients with primary glomerulonephritides (GN) being considered for kidney transplantation, focusing on high-risk subtypes of immunoglobulin A nephropathy, focal segmental glomerulosclerosis, idiopathic membranous glomerulonephritis and membranoproliferative glomerulonephritis.

RECENT FINDINGS

Recurrent glomerulonephritis remains one of the most common causes of allograft loss in kidney transplant recipients. Although the epidemiology and clinical outcomes of glomerulonephritis recurrence occurring after kidney transplantation are relatively well-described, the natural course and optimal treatment strategies of recurrent disease in kidney allografts remain poorly defined. With a greater understanding of the pathophysiology and treatment responses of patients with glomerulonephritis affecting the native kidneys, these discoveries have laid the framework for the potential to improve the management of patients with high-risk glomerulonephritis subtypes being considered for kidney transplantation.

SUMMARY

Advances in the understanding of the underlying immunopathogenesis of primary GN has the potential to offer novel therapeutic options for kidney patients who develop recurrent disease after kidney transplantation. To test the efficacy of novel treatment options in adequately powered clinical trials requires a more detailed understanding of the clinical and histological characteristics of kidney transplant recipients with recurrent glomerulonephritis.

Predictors of poor kidney outcome in children with C3 glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is characterized by heterogeneous clinical presentation, outcome, and predominant C3 accumulation in glomeruli without significant IgG. There is scarce outcome data regarding childhood C3G. We describe clinical and pathological features, treatment and outcomes, and risk factors for progression to chronic kidney disease stage 5 (CKD5) in the largest pediatric series with biopsy-proven C3G.

METHODS

Sixty pediatric patients with C3G from 21 referral centers in Turkey were included in this retrospective study. Patients were categorized according to CKD stage at last visit as CKD5 or non-CKD5. Demographic data, clinicopathologic findings, treatment, and outcome data were compared and possible risk factors for CKD5 progression determined using Cox proportional hazards model.

RESULTS

Mean age at diagnosis was 10.6 ± 3.0 years and follow-up time 48.3 ± 36.3 months. Almost half the patients had gross hematuria and hypertension at diagnosis. Nephritic-nephrotic syndrome was the commonest presenting feature (41.6%) and 1/5 of patients presented with nephrotic syndrome. Membranoproliferative glomerulonephritis was the leading injury pattern, while 40 patients had only C3 staining. Patients with DDD had significantly lower baseline serum albumin compared with C3GN. Eighteen patients received eculizumab. Clinical remission was achieved in 68.3%. At last follow-up, 10 patients (16.6%) developed CKD5: they had lower baseline eGFR and albumin and higher frequency of nephrotic syndrome and dialysis requirement than non-CKD5 patients. Lower serum albumin and eGFR at diagnosis were independent predictors for CKD5 development.

CONCLUSIONS

Children with C3G who have impaired kidney function and hypoalbuminemia at diagnosis should be carefully monitored for risk of progression to CKD5. Graphical abstract.

Eculizumab for pediatric dense deposit disease: A case report and literature review

Dense deposit disease (DDD), a subtype of complement component 3 (C3) glomerulopathy (C3G), results from alternative complement pathway hyperactivity leading to membrane attack complex formation. DDD treatment strategies are limited. We report a case of a 13-year-old girl diagnosed with DDD at 9 years of age, with nephritic and nephrotic syndrome and C3 nephritic factor-negative alternative complement pathway activation. Initial treatment with prednisolone, methylprednisolone pulses (MPs), and mizoribines was effective for 3 years, after which she relapsed. Despite MP treatment followed by prednisolone and mycophenolate mofetil (MMF), her kidney function and proteinuria deteriorated with a high soluble (s)C5b-9 level; she also developed dyspnea and pleural effusion (PE). Three days after the first eculizumab (ECZ) infusion, urine volume increased, respiratory condition improved, PE resolved, and proteinuria decreased in 1 month. Serum creatinine level decreased, and kidney function completely normalized within 7 weeks. The sC5b-9 level normalized, and although proteinuria decreased, nephrotic range proteinuria persisted during ECZ treatment with MMF for 53 weeks, even with increased treatment interval. Thus, complement activation pathway-targeted therapy may be useful for rapidly progressing DDD. Our data support the role of complement pathway abnormalities in C3G with DDD.

Long-Term Outcomes of C3 Glomerulopathy and Immune-Complex Membranoproliferative Glomerulonephritis in Children

Introduction

The reclassification of membranoproliferative glomerulonephritis (MPGN) into immune-complex MPGN (IC-MPGN) and C3 glomerulopathy (C3G) has provided insights into 2 distinct diseases. Although outcomes in adults are poor in both diseases, the pediatric literature is scarce and limited to small, single-center cohorts.

Methods

We conducted a retrospective analysis of 165 pediatric patients across 17 hospitals to compare outcomes between children with IC-MPGN and C3G.

Results

Forty-two percent of patients initially diagnosed with MPGN were reclassified as C3G after a review of renal biopsy reports. There was a trend toward higher serum creatinine levels in patients with C3G compared with IC-MPGN both at diagnosis (mean 168.9 [range 45.4–292.4] vs. 93.7 [range 70.7–116.6] μmol/l, P = 0.25) and after a mean follow-up time of 4 years (mean 145.0 (range −8.1 to 298.1) vs 99.1 (range 46.3–151.9) μmol/l, P = 0.47), although the estimated glomerular filtration rate (eGFR) was not significantly different. Steroid treatment was associated with a significant improvement in eGFR versus no steroids in C3G (mean +43.0 (range 12.9–73.0) vs. −3.0 (range −23.1 to 17.2) ml/min per 1.73 m², P = 0.02) but not in IC-MPGN. Overall kidney function was preserved in both groups although hypertension remained prevalent in 42.5% of the cohort at the last follow-up, and the urine protein/creatinine ratio remained elevated (mean 253.8 [range 91.9–415.7] mg/mmol).

Conclusion

This large pediatric IC-MPGN/C3G cohort revealed nearly half of the patients were misclassified, and there may be a trend toward worse renal prognosis in C3G although they may have greater steroid responsiveness. The overall prognosis appears to be more favorable than in adults; however, persistent hypertension and proteinuria suggest suboptimal disease control.

Clinicopathological features of C3 glomerulopathy in children: a single-center experience

BACKGROUND

C3 glomerulopathy (C3G) is defined by dominant glomerular deposition of C3 and minimal or no immunoglobulin, with two subtypes-dense deposit disease (DDD) and C3 glomerulonephritis (C3GN)-distinguished by features on electron microscopy (EM). Given that this rare disease has generally unfavorable yet highly variable outcomes, we sought out to review the histopathology, complement/genetic studies, and renal outcomes of pediatric patients with C3G at our institution.

METHODS

All native kidney biopsies performed in a single pediatric hospital over a 10-year period were reviewed for features of C3G. Of 589 biopsy reports, we identified 9 patients fulfilling the diagnostic criteria for C3G and retrospectively reviewed their clinical chart and renal biopsy findings.

RESULTS

We identified 4 patients with DDD, 4 with C3GN, and 1 indeterminate case, with features of both C3GN and DDD. Five patients were positive for one or more nephritic factors (C3NeF, C4NeF, C5NeF) with 1 patient additionally positive for complement factor H (CFH) autoantibody. Genetic testing done in 5 of the 9 patients failed to identify any causative mutations. Three patients showed progressive renal dysfunction over a mean follow-up period of 33 months.

CONCLUSIONS

Complement and genetic studies are now routinely recommended for patients with a histopathological diagnosis of C3G. Careful interpretation of these studies and their prognostic and therapeutic implications in conjunction with biopsy findings is needed to further understand the pathophysiology of this rare disease in children.

Compendium of current complement therapeutics

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 many diseases, in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The driving role of complement in a single disease, paroxysmal nocturnal hemoglobinuria (PNH), provoked the development and eventual FDA (US Food and Drug Administration) approval of eculizumab (Soliris™), an anti-C5 antibody, for therapy. Although PNH is very rare, eculizumab provided clinical validation and demonstrated that inhibiting the complement system was not only well-tolerated, but also provided rapid therapy and saved lives. This clinical validation, together with advances in genetic analyses that demonstrated strong associations between complement and common diseases, drove new drug discovery programmes in both academic laboratories and large pharmaceutical companies. Numerous drugs have entered clinical development and several are in phase 3 trials; however, many have fallen by the wayside. Despite this high attrition rate, crucial lessons have been learnt and hurdles to development have become clear. These insights have driven development of next generation anti-complement drugs designed to avoid pitfalls and facilitate patient access. In this article, we do not set out to provide a text-heavy review of complement therapeutics but instead will simply highlight the targets, modalities and current status of the plethora of drugs approved or in clinical development. With such a fast-moving drug development landscape, such a compendium will inevitably become out-dated; however, we provide a snapshot of the current field and illustrate the increased choice that clinicians might enjoy in the future in selecting the best drug for their application, decisions based not only on efficacy but also cost, mechanistic target, modality and route of delivery.

Recurrent and de novo Glomerulonephritis After Kidney Transplantation

The prevalence, pathogenesis, predictors, and natural course of patients with recurrent glomerulonephritis (GN) occurring after kidney transplantation remains incompletely understood, including whether there are differences in the outcomes and advances in the treatment options of specific GN subtypes, including those with de novo GN. Consequently, the treatment options and approaches to recurrent disease are largely extrapolated from the general population, with responses to these treatments in those with recurrent or de novo GN post-transplantation poorly described. Given a greater understanding of the pathogenesis of GN and the development of novel treatment options, it is conceivable that these advances will result in an improved structure in the future management of patients with recurrent or de novo GN. This review focuses on the incidence, genetics, characteristics, clinical course, and risk of allograft failure of patients with recurrent or de novo GN after kidney transplantation, ascertaining potential disparities between “high risk” disease subtypes of IgA nephropathy, idiopathic membranous glomerulonephritis, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis. We will examine in detail the management of patients with high risk GN, including the pre-transplant assessment, post-transplant monitoring, and the available treatment options for disease recurrence. Given the relative paucity of data of patients with recurrent and de novo GN after kidney transplantation, a global effort in collecting comprehensive in-depth data of patients with recurrent and de novo GN as well as novel trial design to test the efficacy of specific treatment strategy in large scale multicenter randomized controlled trials are essential to address the knowledge deficiency in this disease.

C3 glomerulopathy in children: Is there still a place for anti-cellular immunosuppression?

AIM

To contribute additional clinical experience to the paucity of reports on C3 glomerulopathy (C3GP) in children, we are reporting our cohort of 11 children with C3GP, emphasizing the therapeutic options in this peculiar entity.

METHODS

We describe the incidence, manifestation, histopathology findings, follow-up, treatment and outcome of C3GP in 11 children with C3GP by retrospectively analyzing their clinical charts and renal biopsy reports.

RESULTS

Eleven C3GP patients were identified among 240 children who had undergone renal biopsy, accounting for a 4.6% incidence of C3GP. A light microscopy examination showed a membranoproliferative pattern (n = 8), mesangial proliferation (n = 1), a mesangial/membranoproliferative pattern (n = 1) and endocapillary proliferation (n = 1). All children presented with proteinuria of varying degrees, the majority of them with additional hematuria, three with full-blown nephrotic-nephritic syndrome, and two with renal insufficiency at presentation. Very diverse treatments were applied in our cohort of patients, from no specific treatment to different mono or combined anti-cellular immunosuppression treatments, as well as a trial of plasma therapy or eculizumab. Our results are in to some extend in concordance with other studies revealing that an optimal therapy for C3GP is still unknown, but we believe that a trial of classical immunosuppression before eculizumab is still worth trying, while eculizumab can have a beneficial effect, but not in all patients.

CONCLUSION

A diverse histological pattern and clinical picture and no known optimal therapy are a hallmark of C3GP.

Outcome of membranoproliferative glomerulonephritis and C3-glomerulopathy in children and adolescents

BACKGROUND

Membranoproliferative glomerulonephritis (MPGN) is a rare cause of glomerulopathy in children. Recently, a new classification based on immunohistological features has been established. Infections and anomalies in complement-regulating genes, leading to alternative complement pathway activation, are suspected to trigger the disease. Nevertheless, little is known about optimal treatment and outcome in children with immune-complex-MPGN (IC-MPGN) and C3-glomerulopathy (C3G).

METHODS

The method used is retrospective analysis of clinical, histological, and genetic characteristics of 14 pediatric patients with MPGN in two medical centers.

RESULTS

Mean age of the patients was 10.6 ± 4.5 years. Patients were grouped into C3G (n = 6) and IC-MPGN (n = 8). One patient showed a likely pathogenic variant in the CFHR5 gene. All 10 patients had risk polymorphisms in complement-regulating genes. Most patients were treated with ACE inhibition, steroids, and mycophenolate mofetil. Three patients with C3G received eculizumab. Median follow-up was 2.3 years. After 1 year of disease, three patients (two C3G, one IC-MPGN) reached complete, five patients partial (three IC-MPGN, two C3G), and five patients no remission (four IC-MPGN, one C3G). One patient progressed to end-stage renal disease (ESRD) 6 years after disease onset.

CONCLUSIONS

IC-MPGN and C3G are rare disorders in children. Most patients have signs of complement activation associated with risk polymorphisms or likely pathogenic variants in complement-regulating genes. Steroids and mycophenolate mofetil seem to be effective and for some patients, eculizumab might be a treatment option. Outcome is heterogeneous and precise differentiation between IC-MPGN and C3G is still pending.

Kidney Transplantation in C3 Glomerulopathy: A Case Series

RATIONALE & OBJECTIVE

C3 glomerulopathy (C3G), a form of glomerulonephritis associated with dysregulation of the alternative complement pathway, occurs either as dense deposit disease (DDD) or C3 glomerulonephritis (C3GN). Few studies have reported outcomes of patients with C3G after transplantation since its formal classification and the advent of complement-targeting therapies such as eculizumab.

STUDY DESIGN

Case series of C3G.

SETTING & PARTICIPANTS

We reviewed laboratory testing, native and allograft biopsy reports, and clinical charts of the 19 patients (12, C3GN; and 7, DDD) from our C3G registry who underwent transplantation between 1999 and 2016.

RESULTS

During a median follow-up of 76 months, 16 patients had recurrent disease (10 of 12, C3GN; and 6 of 7, DDD), with median time to recurrence of 14 months in C3GN versus 15 months in DDD. Graft failure was more frequent in patients with DDD (6 of 7) than in patients with C3GN (3 of 12), occurred at a median time of 42 months posttransplantation, and was attributed to recurrent disease in half the failures. A rare genetic variant or autoantibody associated with alternative complement pathway abnormalities was detected in 9 of 10 screened patients. Treatment of 7 patients (8 allografts) with eculizumab was associated with variable clinical outcomes.

LIMITATIONS

Incomplete testing for complement pathway abnormalities and genetic defects, incomplete records of HLA antigen matching, lack of centralized biopsy review, and limited sample size.

CONCLUSIONS

In a case series of C3G transplant recipients, the proportion of disease recurrence was high in both C3GN and DDD, although graft loss appeared to occur more frequently in DDD. In a small subset of study patients, eculizumab therapy was not consistently followed by salutary outcomes.

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.

Prevention of Fatal C3 Glomerulopathy by Recombinant Complement Receptor of the Ig Superfamily

Background C3 glomerulopathy (C3G) is a life-threatening kidney disease caused by dysregulation of the alternative pathway of complement (AP) activation. No approved specific therapy is available for C3G, although an anti-C5 mAb has been used off-label in some patients with C3G, with mixed results. Thus, there is an unmet medical need to develop other inhibitors of complement for C3G.Methods We used a murine model of lethal C3G to test the potential efficacy of an Fc fusion protein of complement receptor of the Ig superfamily (CRIg-Fc) in the treatment of C3G. CRIg-Fc binds C3b and inhibits C3 and C5 convertases of the AP. Mice with mutations in the factor H and properdin genes (FH^m/mP^-/-) develop early-onset C3G, with AP consumption, high proteinuria, and lethal crescentic GN.Results Treatment of FH^m/mP^-/- mice with CRIg-Fc, but not a control IgG, inhibited AP activation and diminished the consumption of plasma C3, factor B, and C5. CRIg-Fc-treated FH^m/mP^-/- mice also had significantly improved survival and reduced proteinuria, hematuria, BUN, glomerular C3 fragment, C9 and fibrin deposition, and GN pathology scores.Conclusions Therapeutics developed on the basis of the mechanism of action of soluble CRIg may be effective for the treatment of C3G and should be explored clinically.

Membranoproliferative glomerulonephritis and C3 glomerulopathy in children: change in treatment modality? A report of a case series

Background

Membranoproliferative glomerulonephritis (MPGN) with immune complexes and C3 glomerulopathy (C3G) in children are rare and have a variable outcome, with some patients progressing to end-stage renal disease (ESRD). Mutations in genes encoding regulatory proteins of the alternative complement pathway and of complement C3 (C3) have been identified as concausative factors.

Methods

Three children with MPGN type I, four with C3G, i.e. three with C3 glomerulonephritis (C3GN) and one with dense deposit disease (DDD), were followed. Clinical, autoimmune data, histological characteristics, estimated glomerular filtration rate (eGFR), proteinuria, serum C3, genetic and biochemical analysis were assessed.

Results

The median age at onset was 7.3 years and the median eGFR was 72 mL/min/1.73 m². Six children had marked proteinuria. All were treated with renin-angiotensin-aldosterone system (RAAS) blockers. Three were given one or more immunosuppressive drugs and two eculizumab. At the last median follow-up of 9 years after diagnosis, three children had normal eGFR and no or mild proteinuria on RAAS blockers only. Among four patients without remission of proteinuria, genetic analysis revealed mutations in complement regulator proteins of the alternative pathway. None of the three patients with immunosuppressive treatment achieved partial or complete remission of proteinuria and two progressed to ESRD and renal transplantation. Two patients treated with eculizumab revealed relevant decreases in proteinuria.

Conclusions

In children with MPGN type I and C3G, the outcomes of renal function and response to treatment modality show great variability independent from histological diagnosis at disease onset. In case of severe clinical presentation at disease onset, early genetic and biochemical analysis of the alternative pathway dysregulation is recommended. Treatment with eculizumab appears to be an option to slow disease progression in single cases.

Patterns of Clinical Response to Eculizumab in Patients With C3 Glomerulopathy

BACKGROUND

Cases reports and small series of patients with C3 glomerulopathy have reported variable efficacy of eculizumab.

STUDY DESIGN

Case series of C3 glomerulopathy.

SETTING & PARTICIPANTS

Pediatric and adult patients with C3 glomerulopathy treated with eculizumab between 2010 and 2016 were identified through the C3 glomerulopathy French registry database, and a questionnaire was sent to participating French pediatric and adult nephrology centers, as well as one pediatric referral center in Québec, Canada.

OUTCOMES

Global or partial clinical renal response.

MEASUREMENTS

Evolution of serum creatinine and proteinuria values.

RESULTS

26 patients (13 children/adolescents) were included. 22 (85%) patients had received steroids, plasma exchange, or immunosuppressive therapy before eculizumab, and 3 of them had rapid progression of their kidney disease despite treatment. At the initiation of eculizumab therapy, 11 (42%) patients had chronic kidney disease, 7 (27%) had rapidly progressive disease, and 3 (12%) required dialysis. After eculizumab treatment (median duration, 14 months), 6 (23%) patients had a global clinical response; 6 (23%), a partial clinical response; and 14 (54%), no response. Compared with those who had a partial clinical or no response, patients who had a global clinical response had lower estimated glomerular filtration rates, a more rapidly progressive course, and more extracapillary proliferation on kidney biopsy. Age, extent of renal fibrosis, frequency of nephrotic syndrome, low serum C3 and C3 nephritic factor and elevated soluble C5b-9 concentrations, or complement gene variants did not differ between responders and nonresponders.

LIMITATIONS

Retrospective design without a control group, relatively small number of cases, inclusion of pediatric and adult cases.

CONCLUSIONS

Eculizumab appears to be a potential treatment for patients with crescentic rapidly progressive C3 glomerulopathy. Its benefit in patients with non-rapidly progressing forms seems to be limited.

Treating C3 glomerulopathy with eculizumab

Background

C3 glomerulopathy (C3G) is a rare, but severe glomerular disease with grim prognosis. The complex pathogenesis is just unfolding, and involves acquired as well as inherited dysregulation of the alternative pathway of the complement cascade. Currently, there is no established therapy. Treatment with the C5 complement inhibitor eculizumab may be a therapeutic option. However, due to rarity of the disease, parameters predicting treatment response remain largely unknown.

Methods

Seven patients with C3G (five with C3 glomerulonephritis and two with dense deposit disease) were treated with eculizumab. Subjects underwent biopsy before enrollment. The histopathology, clinical data, and response to eculizumab treatment were analyzed. The key parameters to determine outcome were changes of serum creatinine and urinary protein over time.

Results

After treatment with eculizumab, four subjects showed significantly improved or stable renal function and urinary protein. A positive response occurred between 2 weeks and 6 months after therapy initiation. One subject (with allograft recurrent C3 glomerulonephritis) initially showed a positive response, but relapsed when eculizumab was discontinued, and did not respond after re-initiation of treatment. Two subjects showed impaired renal function and increasing urinary protein despite therapy with eculizumab.

Conclusions

Eculizumab may be a therapeutic option for a subset of C3G patients. The response to eculizumab is heterogeneous, and early as well as continuous treatment may be necessary to prevent disease progression. These findings emphasize the need for studies identifying genetic and functional complement abnormalities that may help to guide eculizumab treatment and predict response.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0802-4) contains supplementary material, which is available to authorized users.

Expanding horizons in complement drug discovery: challenges and emerging strategies

The complement system is best known for its role in innate immunity, providing a first line of defence against infection, maintaining tissue homeostasis by flagging apoptotic cells and debris for removal, and orchestrating crosstalk between adaptive and innate immunity. In a growing number of diseases, complement is known to drive pathogenesis or to contribute as an inflammatory amplifier of a disease trigger. Association of complement with common and devastating diseases has driven an upsurge in complement drug discovery, but despite a wealth of knowledge in the complexities of the cascade, and many decades of effort, very few drugs have progressed to late-stage clinical studies. The reasons for this are becoming clear with difficulties including high target concentration and turnover, lack of clarity around disease mechanism and unwanted side effects. Lessons learnt from drugs which are either approved, or are currently in late-stage development, or have failed and dropped off the drug development landscape, have been invaluable to drive a new generation of innovative drugs which are progressing through clinical development. In this review, the challenges associated with complement drug discovery are discussed and the current drug development landscape is reviewed. The latest approaches to improve drug characteristics are explored and those agents which employ these technologies to improve accessibility to patients are highlighted.

Complement in Non-Antibody-Mediated Kidney Diseases

The complement system is part of the innate immune response that plays important roles in protecting the host from foreign pathogens. The complement components and relative fragment deposition have long been recognized to be strongly involved also in the pathogenesis of autoantibody-related kidney glomerulopathies, leading to direct glomerular injury and recruitment of infiltrating inflammation pathways. More recently, unregulated complement activation has been shown to be associated with progression of non-antibody-mediated kidney diseases, including focal segmental glomerulosclerosis, C3 glomerular disease, thrombotic microangiopathies, or general fibrosis generation in progressive chronic kidney diseases. Some of the specific mechanisms associated with complement activation in these diseases were recently clarified, showing a dominant role of alternative activation pathway. Over the last decade, a growing number of anticomplement agents have been developed, and some of them are being approved for clinical use or already in use. Therefore, anticomplement therapies represent a realistic choice of therapeutic approaches for complement-related diseases. Herein, we review the complement system activation, regulatory mechanisms, their involvement in non-antibody-mediated glomerular diseases, and the recent advances in complement-targeting agents as potential therapeutic strategies.