Eculizumab in a patient with dense-deposit disease

Diagnostic and Prognostic Comparison of Immune-Complex-Mediated Membranoproliferative Glomerulonephritis and C3 Glomerulopathy

Membranoproliferative glomerulonephritis (MPGN) is subdivided into immune-complex-mediated glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G). Classically, MPGN has a membranoproliferative-type pattern, but other morphologies have also been described depending on the time course and phase of the disease. Our aim was to explore whether the two diseases are truly different, or merely represent the same disease process. All 60 eligible adult MPGN patients diagnosed between 2006 and 2017 in the Helsinki University Hospital district, Finland, were reviewed retrospectively and asked for a follow-up outpatient visit for extensive laboratory analyses. Thirty-seven (62%) had IC-MPGN and 23 (38%) C3G (including one patient with dense deposit disease, DDD). EGFR was below normal (≤60 mL/min/1.73 m²) in 67% of the entire study population, 58% had nephrotic range proteinuria, and a significant proportion had paraproteins in their serum or urine. A classical MPGN-type pattern was seen in only 34% of the whole study population and histological features were similarly distributed. Treatments at baseline or during follow-up did not differ between the groups, nor were there significant differences observed in complement activity or component levels at the follow-up visit. The risk of end-stage kidney disease and survival probability were similar in the groups. IC-MPGN and C3G have surprisingly similar characteristics, kidney and overall survival, which suggests that the current subdivision of MPGN does not add substantial clinical value to the assessment of renal prognosis. The high proportion of paraproteins in patient sera or in urine suggests their involvement in disease development.

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.

Acute glomerulonephritis

Glomerulonephritis is a heterogeneous group of disorders that present with a combination of haematuria, proteinuria, hypertension, and reduction in kidney function to a variable degree. Acute presentation with full blown nephritic syndrome or rapidly progressive glomerulonephritis is uncommon and is mainly restricted to patients with post-infectious glomerulonephritis, anti-neutrophil cytoplasmic antibodies-associated vasculitis, and anti-glomerular basement membrane disease. Most frequently, patients present with asymptomatic haematuria and proteinuria with or without reduced kidney function. All glomerulonephritis disorders can show periods of exacerbation, but disease flairs characteristically occur in patients with IgA nephropathy or C3 glomerulopathy. The gold standard for the diagnosis of a glomerulonephritis is a kidney biopsy, with a hallmark glomerular inflammation that translates into various histopathological patterns depending on the location and severity of the glomerular injury. Traditionally, glomerulonephritis was classified on the basis of the different histopathological patterns of injury. In the last few years, substantial progress has been made in unravelling the underlying causes and pathogenetic mechanisms of glomerulonephritis and a causal approach to the classification of glomerulonephritis is now favoured over a pattern-based approach. As such, glomerulonephritis can be broadly classified as immune-complex glomerulonephritis (including infection-related glomerulonephritis, IgA nephropathy, lupus nephritis, and cryoglobulinaemic glomerulonephritis), anti-neutrophil cytoplasmic antibodies-associated (pauci-immune) glomerulonephritis, anti-glomerular basement membrane glomerulonephritis, C3 glomerulopathy, and monoclonal immunoglobulin-associated glomerulonephritis. We provide an overview of the clinical presentation, pathology, and the current therapeutic approach of the main representative disorders in the spectrum of glomerulonephritis.

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.

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.

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.

Evaluation of the children with C3 glomerulopathy

C3 glomerulopathy (C3G) is a clinical spectrum that presents with a variety of symptoms, ranging from a mild disease with asymptomatic microhematuria and/or proteinuria to severe disease with nephritic or nephrotic syndrome and renal impairment. Herein, we aim to document the clinical and laboratory findings, response to immunosuppressive and supportive treatment and prognosis of the children with C3G. We retrospectively reviewed the medical records of patients diagnosed with membranoproliferative glomerulonephritis (MPGN). Kidney biopsy materials were reexamined for the diagnosis of C3G. The inclusion criteria for C3G are the dominant C3 staining with or without scanty immunoglobulins (Ig) deposition on immuno- fluorescence (IF) and MPGN patterns on light microscope. Twelve of 69 patients with MPGN were included in the study based on the definition criteria of C3G. Ten of them had only C3 staining and the rest of the patients had both C3 staining and a small amount of IgG/M staining on IF microscopy. One patient was on remission with only ACEI. The rest of the patients used immunosuppressive treatment and two of them needed eculizumab therapy. One of them did not respond to the treatment of eculizumab and progressed to end-stage renal failure. C3G is a disease characterized by a heterogeneous clinical presentation and outcome. Because of this broad spectrum of disease, treatment may vary widely. We think that complement-targeting therapy with eculizumab should be an alternative option for refractory cases, especially in the early stage of disease, if they did not respond to immunosuppressive treatment.

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.

Treatment of C3 Glomerulopathy in Adult Kidney Transplant Recipients: A Systematic Review

BACKGROUND

C3 glomerulopathy (C3G), a rare glomerular disease mediated by alternative complement pathway dysregulation, is associated with a high rate of recurrence and graft loss after kidney transplantation (KTx). We aimed to assess the efficacy of different treatments for C3G recurrence after KTx.

METHODS

Databases (MEDLINE, EMBASE, and Cochrane Database) were searched from inception through 3 May, 2019. Studies were included that reported outcomes of adult KTx recipients with C3G. Effect estimates from individual studies were combined using the random-effects, generic inverse variance method of DerSimonian and Laird., The protocol for this meta-analysis is registered with PROSPERO (no. CRD42019125718).

RESULTS

Twelve studies (7 cohort studies and 5 case series) consisting of 122 KTx patients with C3G (73 C3 glomerulonephritis (C3GN) and 49 dense deposit disease (DDD)) were included. The pooled estimated rates of allograft loss among KTx patients with C3G were 33% (95% CI: 12-57%) after eculizumab, 42% (95% CI: 2-89%) after therapeutic plasma exchange (TPE), and 81% (95% CI: 50-100%) after rituximab. Subgroup analysis based on type of C3G was performed. Pooled estimated rates of allograft loss in C3GN KTx patients were 22% (95% CI: 5-46%) after eculizumab, 56% (95% CI: 6-100%) after TPE, and 70% (95% CI: 24-100%) after rituximab. Pooled estimated rates of allograft loss in DDD KTx patients were 53% (95% CI: 0-100%) after eculizumab. Data on allograft loss in DDD after TPE (1 case series, 0/2 (0%) allograft loss at 6 months) and rituximab (1 cohort, 3/3 (100%) allograft loss) were limited. Among 66 patients (38 C3GN, 28 DDD) who received no treatment (due to stable allograft function at presentation and/or clinical judgment of physicians), pooled estimated rates of allograft loss were 32% (95% CI: 7-64%) and 53% (95% CI: 28-77%) for C3GN and DDD, respectively. Among treated C3G patients, data on soluble membrane attack complex of complement (sMAC) were limited to patients treated with eculizumab (N = 7). 80% of patients with elevated sMAC before eculizumab responded to treatment. In addition, all patients who responded to eculizumab had normal sMAC levels after post-eculizumab.

CONCLUSIONS

Our study suggests that the lowest incidence of allograft loss (33%) among KTX patients with C3G are those treated with eculizumab. Among those who received no treatment for C3G due to stable allograft function, there is a high incidence of allograft loss of 32% in C3GN and 53% in DDD. sMAC level may help to select good responders to eculizumab.

Clinical course and outcome after kidney transplantation in patients with C3 glomerulonephritis due to CFHR5 nephropathy

BACKGROUND

Complement factor H-related protein 5 (CFHR5) nephropathy is an inherited renal disease characterized by microscopic and synpharyngitic macroscopic haematuria, C3 glomerulonephritis and renal failure. It is caused by an internal duplication of exons 2-3 within the CFHR5 gene resulting in dysregulation of the alternative complement pathway. The clinical characteristics and outcomes of transplanted patients with this rare familial nephropathy remain unknown.

METHODS

This is a retrospective case series study of 17 kidney transplant patients with the established founder mutation, followed-up over a span of 30 years.

RESULTS

The mean (±SD) age of patients at the time of the study and at transplantation was 58.6 ± 9.9 and 46.7 ± 8.8 years, respectively. The 10- and 15-year patient survival rates were 100 and 77.8%, respectively. Proteinuria was present in 33.3% and microscopic haematuria in 58.3% of patients with a functional graft. Serum complement levels were normal in all. 'Confirmed' and 'likely' recurrence of CFHR5 nephropathy were 16.6 and 52.9%, respectively; however, 76.5% of patients had a functional graft after a median of 120 months post-transplantation. Total recurrence was not associated with graft loss (P = 0.171), but was associated with the presence of microscopic haematuria (P = 0.001) and proteinuria (P = 0.018). Graft loss was associated with the presence of proteinuria (P = 0.025).

CONCLUSIONS

We describe for the first time the clinical characteristics and outcome of patients with CFHR5 nephropathy post-transplantation. Despite the recurrence of CFHR5 nephropathy, we provide evidence for a long-term favourable outcome and support the continued provision of kidney transplantation as a renal replacement option in patients with CFHR5 nephropathy.

Complement Activation in Progression of Chronic Kidney Disease

Chronic kidney disease (CKD) is a public health problem worldwide, with increasing incidence and prevalence. The mechanisms underlying the progression to end-stage renal disease (ESRD) is not fully understood. The complement system was traditionally regarded as an important part of innate immunity required for host protection against infection and for maintaining host hemostasis. However, compelling evidence from both clinical and experimental studies has strongly incriminated complement activation as a pivotal pathogenic mediator of the development of multiple renal diseases and progressive replacement of functioning nephrons by fibrosis. Both anaphylatoxins, i.e., C3a and C5a, and membrane attack complex (MAC) contribute to the damage that occurs during chronic renal progression through various mechanisms including direct proinflammatory and fibrogenic activity, chemotactic effect, activation of the renal renin-angiotensin system, and enhancement of T-cell immunity. Evolving understanding of the mechanisms of complement-mediated renal injury has led to the emergence of complement-targeting therapeutics. A variety of specific antibodies and inhibitors targeting complement components have shown efficacy in reducing disease in animal models. Moreover, building on these advances, targeting complement has gained encouraging success in treating patients with renal diseases such as atypical hemolytic uremic syndrome (aHUS). Nevertheless, it still requires a great deal of effort to develop inhibitors that can be applied to treat more patients effectively in routine clinical practice.

Autoimmune abnormalities of the alternative complement pathway in membranoproliferative glomerulonephritis and C3 glomerulopathy

Membranoproliferative glomerulonephritis (MPGN) is a rare chronic kidney disease associated with complement activation. Recent immunofluorescence-based classification distinguishes between immune complex (IC)-mediated MPGN, with glomerular IgG and C3 deposits, and C3 glomerulopathies (C3G), with predominant C3 deposits. Genetic and autoimmune abnormalities causing hyperactivation of the complement alternative pathway have been found as frequently in patients with immune complex-associated MPGN (IC-MPGN) as in those with C3G. In the last decade, there have been great advances in research into the autoimmune causes of IC-MPGN and C3G. The complement-activating autoantibodies called C3-nephritic factors (C3NeFs), which are present in 40-80% of patients, form a heterogeneous group of autoantibodies that stabilise the C3 convertase or the C5 convertase of the alternative pathway or both. A few patients, mainly with IC-MPGN, carry autoantibodies directed against the two components of the alternative pathway C3 convertase, factors B and C3b. Finally, autoantibodies against factor H, the main regulator of the alternative pathway, have been reported in a small proportion of patients with IC-MPGN or C3G. The identification of distinct pathogenetic patterns leading to kidney injury and of targets in the complement cascade may pave the way for tailored therapies for IC-MPGN and C3G, with specific complement inhibitors in the development pipeline.

C3-Glomerulopathy Autoantibodies Mediate Distinct Effects on Complement C3- and C5-Convertases

C3 glomerulopathy (C3G) is a severe kidney disease, which is caused by defective regulation of the alternative complement pathway. Disease pathogenesis is heterogeneous and is caused by both autoimmune and genetic factors. Here we characterized IgG autoantibodies derived from 33 patients with autoimmune C3 glomerulopathy. Serum antibodies from all 33 patients as well as purified IgGs bound to the in vitro assembled C3-convertase. Noteworthy, two groups of antibodies were identified: group 1 with strong (12 patients) and group 2 with weak binding C3-convertase autoantibodies (22 patients). C3Nef, as evaluated in a standard C3Nef assay, was identified in serum from 19 patients, which included patients from group 1 as well as group 2. The C3-convertase binding profile was independent of C3Nef. Group 1 antibodies, but not the group 2 antibodies stabilized the C3-convertase, and protected the enzyme from dissociation by Factor H. Also, only group 1 antibodies induced C3a release. However, both group 1 and group 2 autoantibodies bound to the C5-convertase and induced C5a generation, which was inhibited by monoclonal anti-C5 antibody Eculizumab in vitro. In summary, group 1 antibodies are composed of C3Nef and C5Nef antibodies and likely over-activate the complement system, as seen in hemolytic assays. Group 2 antibodies show predominantly C5Nef like activities and stabilize the C5 but not the C3-convertase. Altogether, these different profiles not only reveal a heterogeneity of the autoimmune forms of C3G (MPGN), they also show that in diagnosis of C3G not all autoimmune forms are identified and thus more vigorous autoantibody testing should be performed.

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.

C5 Convertase Blockade in Membranoproliferative Glomerulonephritis: A Single-Arm Clinical Trial

RATIONALE & OBJECTIVE

Primary membranoproliferative glomerulonephritis (MPGN) is a rare glomerulopathy characterized by complement dysregulation. MPGN progresses rapidly to kidney failure when it is associated with nephrotic syndrome. We assessed the effects of C5 convertase blockade in patients with MPGN and terminal complement activation.

STUDY DESIGN

Prospective off-on-off-on open-label clinical trial.

SETTING & PARTICIPANTS

Consenting patients with immune complex-mediated MPGN (n=6) or C3 glomerulonephritis (n=4) with sC5b-9 (serum complement membrane attack complex) plasma levels>1,000ng/mL and 24-hour proteinuria with protein excretion>3.5g identified from the Italian Registry of MPGN and followed up at the Istituto di Ricerche Farmacologiche Mario Negri IRCCS (Bergamo, Italy) between March 4, 2014, and January 7, 2015.

INTERVENTION

Anti-C5 monoclonal antibody eculizumab administered during 2 sequential 48-week treatment periods separated by one 12-week washout period.

OUTCOMES

Primary outcome was change in 24-hour proteinuria (median of 3 consecutive measurements) at 24 and 48 weeks.

RESULTS

Median proteinuria decreased from protein excretion of 6.03 (interquartile range [IQR], 4.8-12.4) g/d at baseline to 3.74 (IQR, 3.2-4.4) g/d at 24 weeks (P=0.01) and to 5.06 (IQR, 3.1-5.8) g/d (P=0.006) at 48 weeks of treatment, recovered toward baseline during the washout period, and did not significantly decrease thereafter. Hypoalbuminemia, dyslipidemia, and glomerular sieving function improved during the first treatment period. 3 patients achieved partial remission of nephrotic syndrome and all had undetectable C3 nephritic factors before treatment. Mean measured glomerular filtration rate was 69.7±35.2 versus 87.4±55.1 and 75.8±42.7 versus 76.6±44.1mL/min/1.73m² at the start versus the end of the first and second treatment periods, respectively, among all 10 study participants. Unlike C3, sC5b-9 plasma levels normalized during both treatment periods and recovered toward baseline during the washout in all patients.

LIMITATIONS

Single-arm design, small sample size.

CONCLUSIONS

Eculizumab blunted terminal complement activation in all patients with immune complex-mediated MPGN or C3 glomerulonephritis and nephrotic syndrome, but persistently reduced proteinuria in just a subgroup.

TRIAL REGISTRATION

Registered in the EU Clinical Trials Register with study no. 2013-003826-10.

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.

Complement-mediated renal diseases after kidney transplantation - current diagnostic and therapeutic options in de novo and recurrent diseases

For decades, kidney diseases related to inappropriate complement activity, such as atypical hemolytic uremic syndrome and C3 glomerulopathy (a subtype of membranoproliferative glomerulonephritis), have mostly been complicated by worsened prognoses and rapid progression to end-stage renal failure. Alternative complement pathway dysregulation, whether congenital or acquired, is well-recognized as the main driver of the disease process in these patients. The list of triggers include: surgery, infection, immunologic factors, pregnancy and medications. The advent of complement activation blockade, however, revolutionized the clinical course and outcome of these diseases, rendering transplantation a viable option for patients who were previously considered as non-transplantable cases. Several less-costly therapeutic lines and likely better efficacy and safety profiles are currently underway. In view of the challenging nature of diagnosing these diseases and the long-term cost implications, a multidisciplinary approach including the nephrologist, renal pathologist and the genetic laboratory is required to help improve overall care of these patients and draw the optimum therapeutic plan.

Unraveling the Molecular Mechanisms Underlying Complement Dysregulation by Nephritic Factors in C3G and IC-MPGN

Membranoproliferative glomerulonephritis (MPGN) was recently classified as C3 glomerulopathies (C3G), and immune-complex (IC) mediated MPGN. Dysregulation of the complement alternative pathway, driven by acquired and/or genetic defects, plays a pathogenetic role in C3G. However, alternative pathway abnormalities were also found in IC-MPGN. The most common acquired drivers are the C3 nephritic factors (C3NeFs), heterogeneous autoantibodies that stabilize the C3 convertase, C3bBb. C3NeFs are traditionally detected by hemolytic assays based on sheep erythrocyte lysis, which however do not provide a direct molecular estimation of C3bBb formation and decay. We set up a microplate/western blot assay that specifically detects and quantifies C3bBb, and its precursor, the C3 proconvertase C3bB, to investigate the complex mechanistic effects of C3NeFs from patients with primary IC-MPGN (n = 13) and C3G (n = 13). In the absence of properdin, 9/26 patients had C3NeF IgGs stabilizing C3bBb against spontaneous and FH-accelerated decay. In the presence of properdin the IgGs of all but one patient had C3bBb-stabilizing activity. Properdin-independent C3NeFs were identified mostly in DDD patients, while properdin-dependent C3NeFs associated with either C3GN or IC-MPGN and with higher incidence of nephrotic syndrome. When we grouped patients based on our recent cluster analysis, patients in cluster 3, with highly electron-dense intramembranous deposits, low C3, and mostly normal sC5b-9 levels, had a higher prevalence of properdin-independent C3NeFs than patients in clusters 1 and 2. Conversely, about 70% of cluster 1 and 2 patients, with subendothelial, subepithelial, and mesangial deposits, low C3 levels and high sC5b-9 levels, had properdin-dependent C3NeFs. The flexibility of the assay allowed us to get deep insights into C3NeF mechanisms of action, showing that: (1) most C3NeFs bind strongly and irreversibly to C3 convertase; (2) C3NeFs and FH recognize different epitopes in C3 convertase; (3) C3NeFs bind rapidly to C3 convertase and antagonize the decay accelerating activity of FH on newly formed complexes; (4) C3NeFs do not affect formation and stability of the C3 proconvertase. Thus, our study provides a molecular approach to detecting and characterizing C3NeFs. The results highlight different mechanisms of complement dysregulation resulting in different complement profiles and patterns of glomerular injury, and this may have therapeutic implications.

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.

Eculizumab as salvage therapy for recurrent monoclonal gammopathy-induced C3 glomerulopathy in a kidney allograft

Background

Monoclonal gammopathy causes several kinds of renal pathology. A rare and special form is monoclonal gammopathy-induced C3 glomerulopathy (MG-C3G). Like idiopathic C3G, MG-C3G frequently leads to end-stage renal disease. MG-C3G frequently recurs after renal transplantation, leading to graft failure in most of the patients. While there is some evidence for successful treatment of recurrent idiopathic C3 glomerulopathy with eculizumab after renal transplantation, nothing is known about its efficacy in the setting of recurrent MG-C3G.

Case presentation

We report a patient with recurrent MG-C3G in a renal allograft that was successfully treated with eculizumab in addition to standard immunosuppression. He had early recurrence of MG-C3G 2 months after transplantation. His graft function successively declined despite high dose steroids and plasmapheresis. Only after therapy with three cycles of bortezomib and continuous therapy with eculizumab, his graft function stabilized. He was still in clinical remission after 28 months of follow-up without having experienced major infectious complications.

Conclusions

Eculizumab may be a safe and effective treatment of recurrent MG-C3G. Because of the high and early recurrence risk, renal transplantation should be reviewed carefully for every individual patient. Subsequent hematopoietic stem cell transplantation may ameliorate long-term renal allograft survival. Eculizumab might serve as a bridging therapy until stem cell transplantation.

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.

C3 Glomerulopathy and Atypical Hemolytic Uremic Syndrome: Two Important Manifestations of Complement System Dysfunction

The advances in our understanding of the alternative pathway have emphasized that uncontrolled hyperactivity of this pathway causes 2 distinct disorders that adversely impact the kidney. In the so-called atypical hemolytic uremic syndrome (aHUS), renal dysfunction occurs along with thrombocytopenia, anemia, and target organ injury to multiple organs, most commonly the kidney. On the other hand, in the so-termed C3 glomerulopathy, kidney involvement is not associated with thrombocytopenia, anemia, or other system involvement. In this report, we present 2 cases of alternative pathway dysfunction. The 60-year-old female patient had biopsy-proven C3 glomerulopathy, while the 32-year-old female patient was diagnosed with aHUS based on renal dysfunction, thrombocytopenia, anemia, and normal ADAMTS-13 level. The aHUS patient was successfully treated with the monoclonal antibody (eculizumab) for complement blockade. The patient with C3 glomerulopathy did not receive the monoclonal antibody. In this patient, management focused on blood pressure and proteinuria control with an angiotensin-converting enzyme inhibitor. This article focuses on the clinical differences, pathophysiology, and treatment of aHUS and C3 glomerulopathy.

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.

Recurrence of primary glomerulonephritis: Review of the current evidence

In view of the availability of new immunosuppression strategies, the recurrence of allograft glomerulonephritis (GN) are reported to be increasing with time post transplantation. Recent advances in understanding the pathogenesis of the GN recurrent disease provided a better chance to develop new strategies to deal with the GN recurrence. Recurrent GN diseases manifest with a variable course, stubborn behavior, and poor response to therapy. Some types of GN lead to rapid decline of kidney function resulting in a frustrating return to maintenance dialysis. This subgroup of aggressive diseases actually requires intensive efforts to ascertain their pathogenesis so that strategy could be implemented for better allograft survival. Epidemiology of native glomerulonephritis as the cause of end-stage renal failure and subsequent recurrence of individual glomerulonephritis after renal transplantation was evaluated using data from various registries, and pathogenesis of individual glomerulonephritis is discussed. The following review is aimed to define current protocols of the recurrent primary glomerulonephritis therapy.

Complement C5-inhibiting therapy for the thrombotic microangiopathies: accumulating evidence, but not a panacea

Thrombotic microangiopathy (TMA), characterized by organ injury occurring consequent to severe endothelial damage, can manifest in a diverse range of diseases. In complement-mediated atypical haemolytic uraemic syndrome (aHUS) a primary defect in complement, such as a mutation or autoantibody leading to over activation of the alternative pathway, predisposes to the development of disease, usually following exposure to an environmental trigger. The elucidation of the pathogenesis of aHUS resulted in the successful introduction of the complement inhibitor eculizumab into clinical practice. In other TMAs, although complement activation may be seen, its role in the pathogenesis remains to be confirmed by an interventional trial. Although many case reports in TMAs other than complement-mediated aHUS hint at efficacy, publication bias, concurrent therapies and in some cases the self-limiting nature of disease make broader interpretation difficult. In this article, we will review the evidence for the role of complement inhibition in complement-mediated aHUS and other TMAs.

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.

Retinal findings in membranoproliferative glomerulonephritis

Purpose

To assess the evolution of retinal findings in patients with membranoproliferative glomerulonephritis (MPGN) by funduscopy, intravenous fluorescein angiography and optical coherence tomography.

Observations

Three women and one man were followed for a period of 1.5–37 years. Four patients (8 eyes) had drusen detected at first fundus exam at age 24, 29, 50 and 55. Three patients (6 eyes) had diffuse thickening of Bruch's membrane, and two patients (3 eyes) had detachment of the retinal pigment epithelium with serous retinal detachment. Drusen tended to widen over a period of 10-year follow-up in one case.

Conclusions and importance

Drusen remain the ocular stigmata for MPGN occuring at an early age. The retinal disease is progressive with gradual thickening of Bruch's membrane and occurrence of retinal pigment epithelium detachment.

Rituximab for Treatment of Membranoproliferative Glomerulonephritis and C3 Glomerulopathies

Membranoproliferative glomerulonephritis (MPGN) is a histological pattern of injury resulting from predominantly subendothelial and mesangial deposition of immunoglobulins or complement factors with subsequent inflammation and proliferation particularly of the glomerular basement membrane. Recent classification of MPGN is based on pathogenesis dividing MPGN into immunoglobulin-associated MPGN and complement-mediated C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). Current guidelines suggest treatment with steroids, cytotoxic agents with or without plasmapheresis only for subjects with progressive disease, that is, nephrotic range proteinuria and decline of renal function. Rituximab, a chimeric B-cell depleting anti-CD20 antibody, has emerged in the last decade as a treatment option for patients with primary glomerular diseases such as minimal change disease, focal-segmental glomerulosclerosis, or idiopathic membranous nephropathy. However, data on the use of rituximab in MPGN, C3GN, and DDD are limited to case reports and retrospective case series. Patients with immunoglobulin-associated and idiopathic MPGN who were treated with rituximab showed partial and complete responses in the majorities of cases. However, rituximab was not effective in few cases of C3GN and DDD. Despite promising results in immunoglobulin-associated and idiopathic MPGN, current evidence on this treatment remains weak, and controlled and prospective data are urgently needed.

C5 inhibition prevents renal failure in a mouse model of lethal C3 glomerulopathy

C3 glomerulopathy is a potentially life-threatening disease of the kidney caused by dysregulated alternative pathway complement activation. The specific complement mediator(s) responsible for kidney injury in C3 glomerulopathy are yet to be defined and no specific therapy is currently available. We previously developed a mouse model of lethal C3 glomerulopathy with factor H and properdin gene double mutations. Therefore, we used this model to examine the role of C5 and C5a receptor (C5aR) in the pathogenesis of the disease. Disease severity in these factor H/properdin double-mutant mice was found to be correlated with plasma C5 levels, and prophylactic anti-C5 mAb therapy was effective in preventing lethal C3 glomerulopathy. When given to these double-mutant mice that had already developed active disease with severe proteinuria, anti-C5 mAb treatment also prevented death in half of the mice. Deficiency of C5aR significantly reduced disease severity, suggesting that C5aR-mediated inflammation contributed to C3 glomerulopathy. Thus, C5 and C5aR have a critical role in C3 glomerulopathy. Hence, early intervention targeting these pathways may be an effective therapeutic strategy for patients with C3 glomerulopathy.

C3 Glomerulopathy

Recent advances in our understanding of the disease pathology of membranoproliferative glomerulonephritis has resulted in its re-classification as complement C3 glomerulopathy (C3G) and immune complex-mediated glomerulonephritis (IC-GN). The new consensus is based on its underlying pathomechanism, with a key pathogenetic role for the complement alternative pathway (AP), rather than on histomorphological characteristics. In C3G, loss of AP regulation leads to predominant glomerular C3 deposition, which distinguishes C3G from IC-GN with predominant immunoglobulin G staining. Electron microscopy further subdivides C3G into C3 glomerulonephritis and dense deposit disease depending on the presence and distribution pattern of electron-dense deposits within the glomerular filter. Mutations or autoantibodies affecting the function of AP activators or regulators, in particular the decay of the C3 convertase (C3 nephritic factor), have been detected in up to 80 % of C3G patients. The natural outcome of C3G is heterogeneous, but 50 % of patients progress slowly and reach end-stage renal disease within 10-15 years. The new classification not only marks significant advancement in the pathogenic understanding of this rare disease, but also opens doors towards more specific treatment with the potential for improved outcomes.

Atypical hemolytic uremic syndrome and C3 glomerulopathy: conclusions from a "Kidney Disease: Improving Global Outcomes" (KDIGO) Controversies Conference

In both atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) complement plays a primary role in disease pathogenesis. Herein we report the outcome of a 2015 Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference where key issues in the management of these 2 diseases were considered by a global panel of experts. Areas addressed included renal pathology, clinical phenotype and assessment, genetic drivers of disease, acquired drivers of disease, and treatment strategies. In order to help guide clinicians who are caring for such patients, recommendations for best treatment strategies were discussed at length, providing the evidence base underpinning current treatment options. Knowledge gaps were identified and a prioritized research agenda was proposed to resolve outstanding controversial issues.

Paraprotein-Related Kidney Disease: Glomerular Diseases Associated with Paraproteinemias

Paraproteins are monoclonal Igs that accumulate in blood as a result of abnormal excess production. These circulating proteins cause a diversity of kidney disorders that are increasingly being comanaged by nephrologists. In this review, we discuss paraprotein-related diseases that affect the glomerulus. We provide a broad overview of diseases characterized by nonorganized deposits, such as monoclonal Ig deposition disease (MIDD), proliferative GN with monoclonal Ig deposits (PGNMID), and C3 glomerulopathy, as well as those characterized by organized deposits, such as amyloidosis, immunotactoid glomerulopathy, fibrillary GN, and cryoglobulinemic GN, and rarer disorders, such as monoclonal crystalline glomerulopathies, paraprotein-related thrombotic microangiopathies, and membranous-like glomerulopathy with masked IgGκ deposits. This review will provide the nephrologist with an up to date understanding of these entities and highlight the areas of deficit in evidence and future lines of research.

Complement inhibition in C3 glomerulopathy

C3 glomerulopathy (C3G) describes a spectrum of glomerular diseases defined by shared renal biopsy pathology: a predominance of C3 deposition on immunofluorescence with electron microscopy permitting disease sub-classification. Complement dysregulation underlies the observed pathology, a causal relationship that is supported by well described studies of genetic and acquired drivers of disease. In this article, we provide an overview of the features of C3G, including a discussion of disease definition and a review of the causal role of complement. We discuss molecular markers of disease and how biomarkers are informing our evolving understanding of underlying pathology. Research advances are laying the foundation for complement inhibition as a targeted approach to treatment of C3G.

Reclassification of membranoproliferative glomerulonephritis: Identification of a new GN: C3GN

This review revises the reclassification of the membranoproliferative glomerulonephritis (MPGN) after the consensus conference that by 2015 reclassified all the glomerulonephritis basing on etiology and pathogenesis, instead of the histomorphological aspects. After reclassification, two types of MPGN are to date recognized: The immunocomplexes mediated MPGN and the complement mediated MPGN. The latter type is more extensively described in the review either because several of these entities are completely new or because the improved knowledge of the complement cascade allowed for new diagnostic and therapeutic approaches. Overall the complement mediated MPGN are related to acquired or genetic cause. The presence of circulating auto antibodies is the principal acquired cause. Genetic wide association studies and family studies allowed to recognize genetic mutations of different types as causes of the complement dysregulation. The complement cascade is a complex phenomenon and activating factors and regulating factors should be distinguished. Genetic mutations causing abnormalities either in activating or in regulating factors have been described. The diagnosis of the complement mediated MPGN requires a complete study of all these different complement factors. As a consequence, new therapeutic approaches are becoming available. Indeed, in addition to a nonspecific treatment and to the immunosuppression that has the aim to block the auto antibodies production, the specific inhibition of complement activation is relatively new and may act either blocking the C5 convertase or the C3 convertase. The drugs acting on C3 convertase are still in different phases of clinical development and might represent drugs for the future. Overall the authors consider that one of the principal problems in finding new types of drugs are both the rarity of the disease and the consequent poor interest in the marketing and the lack of large international cooperative studies.

Complement-Mediated Glomerular Diseases: A Tale of 3 Pathways

A renewed interest in the role of complement in the pathogenesis of glomerular diseases has improved our understanding of their basic, underlying physiology. All 3 complement pathways—classical, lectin, and alternative—have been implicated in glomerular lesions both rare (e.g., dense deposit disease) and common (e.g., IgA nephropathy). Here we review the basic function of these pathways and highlight, with a disease-specific focus, how activation can lead to glomerular injury. We end by exploring the promise of complement-targeted therapies as disease-specific interventions for glomerular diseases.

Differences in clinical findings, pathology, and outcomes between C3 glomerulonephritis and membranoproliferative glomerulonephritis

BACKGROUND

To clarify the clinical manifestations of pediatric complement component C3 glomerulonephritis (C3GN), we retrospectively evaluated differences in the clinicopathological findings and prognosis between C3GN and immune-complex-mediated membranoproliferative glomerulonephritis (IC-MPGN).

METHODS

Thirty-seven patients diagnosed with "idiopathic MPGN" were enrolled in this retrospective study. The patients were divided into two groups, with Group 1 consisting of 19 patients diagnosed with IC-MPGN and Group 2 consisting of 18 patients diagnosed with C3GN. The clinical findings and the prognosis were investigated for both groups.

RESULTS

Thirteen patients in Group 2 were identified by mandatory annual school screening for urinary abnormalities. The incidence of macro-hematuria and the frequency of low serum C4 values were lower in Group 2 patients than in Group 1 patients. At the time of the second renal biopsy, urinary protein excretion, incidence of hematuria, frequency of low serum C3 values, and scores for mesangial proliferation, glomerular sclerosis, and interstitial fibrosis were higher in Group 2 patients than in Group 1 patients. At the most recent follow-up examination, the number of patients categorized as non-responding or with end-stage renal disease was higher in Group 2 patients than in Group 1 patients.

CONCLUSIONS

Our results suggest that the treatment response and prognosis of patients with C3GN are worse than those of patients with IC-mediated MPGN. Therefore, in the clinical context regarding treatment options and prognosis, it may be useful to classify idiopathic MPGN as C3GN or IC-MPGN. In addition, long-term follow-up of C3GN is necessary.

Modeling complement-driven diseases in transgenic mice: Values and limitations

Remarkable advances have been made over past decades in understanding the pathogenesis of complement-mediated diseases. This has led to development of new therapies for, and in some cases re-classification of, complement-driven diseases. This success is due to not only insight from human patients but also studies using transgenic animal models. Animal models that mimic human diseases are useful tools to understand the mechanism of disease and develop new therapies but there are also limitations due to species differences in their complement systems. This review provides a summary of transgenic animal models for three human diseases that are at the forefront of anti-complement therapy, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). They are discussed here as examples to highlight the values and limitations of animal modeling in complement-driven diseases.

Primary glomerulonephritides

Most glomerulonephritides, even the more common types, are rare diseases. They are nevertheless important since they frequently affect young people, often cannot be cured, and can lead to chronic kidney disease, including end-stage renal failure, with associated morbidity and cost. For example, in young adults, IgA nephropathy is the most common cause of end-stage renal disease. In this Seminar, we summarise existing knowledge of clinical signs, pathogenesis, prognosis, and treatment of glomerulonephritides, with a particular focus on data published between 2008 and 2015, and the most common European glomerulonephritis types, namely IgA nephropathy, membranous glomerulonephritis, minimal change disease, focal segmental glomerulosclerosis, membranoproliferative glomerulonephritis, and the rare complement-associated glomerulonephritides such as dense deposit disease and C3 glomerulonephritis.

Kidney transplant outcomes in familial C3 glomerulopathy

C3 glomerulopathy, a newly designated entity, is characterized by glomerular disease associated with dysregulation of the alternative complement pathway and is a rare cause of end-stage kidney disease. Overall disease characteristics that include clinical presentation, laboratory assessment, histopathology and genetic background have only been unravelled in recent years and have led to the development of anti-complement therapies targeting different levels of the alternative pathway. We describe the long-term outcomes following kidney transplantation in an Irish family with familial C3 glomerulopathy due to a hybrid CFHR3-1 gene.

Biologic agents in the treatment of glomerulonephritides

Current immunosuppression strategies in the treatment of glomerulonephritides remain unsatisfactory, especially in glomerular diseases that are frequently relapsing or are resistant to treatment. Toxicities associated with the use of drugs with non-specific targets for the immune response result in treatment non-compliance, and increase morbidity and mortality in these patients. Advances in our understanding of the immunopathogenesis of glomerulonephritis and the availability of biologics have led to their successful use in the treatment of immune-mediated glomerular diseases. Biologics are usually very large complex molecules, often produced using recombinant DNA technology and manufactured in a living system such as a microorganism, or plant or animal cells. They are novel agents that can target specific immune cell types, cytokines or immune pathways involved in the pathogenesis of these disorders. It is attractive to consider that, given their specific mode of action, these agents can potentially offer a more directed and effective immunosuppression, with side-effect profiles that are much more desirable. However, there have been few randomized controlled trials comparing biologic agents to conventional immunosuppression, and in many of these studies the side-effect profiles have been disappointingly similar. In this review, we will examine the rationale, efficacy and safety of some commonly used biologics in the treatment of primary and secondary glomerulonephritides. We will also discuss some of the key challenges that may be encountered with the use of biologics in treating glomerulonephritis in the future.

Discontinuation of dialysis with eculizumab therapy in a pediatric patient with dense deposit disease

BACKGROUND

Dense deposit disease (DDD) is a rare glomerular disease caused by an uncontrolled activation of the alternative complement pathway leading to end-stage renal disease in 50 % of patients. As such, DDD has been classified within the spectrum of complement component 3 (C3) glomerulopathies due to its pathogenesis from alternative pathway dysregulation. Conventional immunosuppressive therapies have no proven effectiveness. Eculizumab, a terminal complement inhibitor, has been reported to mitigate disease in some cases.

CASE-DIAGNOSIS/TREATMENT

We report on the efficacy of eculizumab in a pediatric patient who failed to respond to cyclophosphamide, corticosteroids, and plasma exchange. Complement biomarker profiling was remarkable for low serum C3, low properdin, and elevated soluble C5b-9. Consistent with these findings, the alternative pathway functional assay was abnormally low, indicative of alternative pathway activity, although neither C3-nephritic factors nor Factor H autoantibodies were detected. Eculizumab therapy was associated with significant improvement in proteinuria and renal function allowing discontinuation of hemodialysis (HD). Repeat C3 and soluble C5b-9 levels normalized, showing that terminal complement pathway activity was successfully blocked while the patient was receiving eculizumab therapy. Repeat testing for alternative pathway activation allowed for a successful decrease in eculizumab dosing.

CONCLUSIONS

The case reported here demonstrates the successful recovery of renal function in a pediatric patient on HD following the use of eculizumab.

[Clinical approach to primary membranoproliferative glomerulonephritis]

Membranoproliferative glomerulonephritis represent a heterogeneous group of nephropathies. During the last five years, our understanding of membranoproliferative glomerulonephritis has greatly improved. Animal models and the study of complement genetics led to the dissection of the physiopathology of membranoproliferative glomerulonephritis, to the individualization of a new entity, C3 glomerulopathy, and to a new classification of these nephropathies. The study of large cohorts has also changed the clinical picture of membranoproliferative glomerulonephritis that has been long dominated by the severity of a single type of dense deposits disease. Finally, the rediscovery of complement through the study of the atypical haemolytic uremic syndrome and the availability in clinical practice of complement inhibitors have paved the way for new therapeutic approaches of membranoproliferative glomerulonephritis.

Biologics for the treatment of autoimmune renal diseases

Biological therapeutics (biologics) that target autoimmune responses and inflammatory injury pathways have a marked beneficial impact on the management of many chronic diseases, including rheumatoid arthritis, psoriasis, inflammatory bowel disease, and ankylosing spondylitis. Accumulating data suggest that a growing number of renal diseases result from autoimmune injury - including lupus nephritis, IgA nephropathy, anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, autoimmune (formerly idiopathic) membranous nephropathy, anti-glomerular basement membrane glomerulonephritis, and C3 nephropathy - and one can speculate that biologics might also be applicable to these diseases. As many autoimmune renal diseases are relatively uncommon, with long natural histories and diverse outcomes, clinical trials that aim to validate potentially useful biologics are difficult to design and/or perform. Some excellent consortia are undertaking cohort studies and clinical trials, but more multicentre international collaborations are needed to advance the introduction of new biologics to patients with autoimmune renal disorders. This Review discusses the key molecules that direct injurious inflammation and the biologics that are available to modulate them. The opportunities and challenges for the introduction of relevant biologics into treatment protocols for autoimmune renal diseases are also discussed.