Eculizumab in a patient with dense-deposit disease

Retinal disease in the C3 glomerulopathies and the risk of impaired vision

BACKGROUND

Dense deposit disease and atypical hemolytic uremic syndrome are often caused by Complement Factor H (CFH) mutations. This study describes the retinal abnormalities in dense deposit disease and, for the first time, atypical haemolytic uremic syndrome. It also reviews our understanding of drusen pathogenesis and their relevance for glomerular disease.

METHODS

Six individuals with dense deposit disease and one with atypical haemolytic uremic syndrome were studied from 2 to 40 years after presentation. Five had renal transplants. All four who had genetic testing had CFH mutations. Individuals underwent ophthalmological review and retinal photography, and in some cases, optical coherence tomography, and further tests of retinal function.

RESULTS

All subjects with dense deposit disease had impaired night vision and retinal drusen or whitish-yellow deposits. Retinal atrophy, pigmentation, and hemorrhage were common. In late disease, peripheral vision was restricted, central vision was distorted, and there were scotoma from sub-retinal choroidal neovascular membranes and atypical serous retinopathy. Drusen were present but less prominent in the young person with atypical uremic syndrome due to a heterozygous CFH mutation.

CONCLUSIONS

Drusen are common in forms of C3 glomerulopathy caused by compound heterozygous or heterozygous CFH mutations. They are useful diagnostically but also impair vision. Drusen have an identical composition to glomerular deposits. They are also identical to the drusen of age-related macular degeneration, and may respond to the same treatments. Individuals with a C3 glomerulopathy should be assessed ophthalmologically at diagnosis, and monitored regularly for vision-threatening complications.

Insights into the Effects of Complement Factor H on the Assembly and Decay of the Alternative Pathway C3 Proconvertase and C3 Convertase

The activated fragment of C3 (C3b) and factor B form the C3 proconvertase (C3bB), which is cleaved by factor D to C3 convertase (C3bBb). Older studies (Conrad, D. H., Carlo, J. R., and Ruddy, S. (1978)J. Exp. Med.147, 1792-1805; Pangburn, M. K., and Müller-Eberhard, H. J. (1978)Proc. Natl. Acad. Sci. U.S.A.75, 2416-2420; Kazatchkine, M. D., Fearon, D. T., and Austen, K. F. (1979)J. Immunol.122, 75-81) indicated that the complement alternative pathway regulator factor H (FH) competes with factor B for C3b binding; however, the capability of FH to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favor C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blotting techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on C3bB assembly and decay and C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with factor B for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as reported previously, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, because blocking decay with properdin and C3 nephritic factor did not restore C3bBb formation. FH almost completely prevented release of the smaller cleavage subunit of FB (Ba), without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, the inhibitory effect of FH on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay acceleration. Further studies are required to confirm these findings in physiological cell-based settings.

Novel factor H mutation associated with familial membranoproliferative glomerulonephritis type I

BACKGROUND

Idiopathic membranoproliferative glomerulonephritis (MPGN) is a rare disease, accounting for 3-5% of all cases of primary nephritic syndrome. We report an uncommon case of familial MPGN type I associated with a new mutation in the complement factor H gene (CFH).

METHODS

Clinical data were collected on three siblings with known factor H deficiency who presented with MPGN. All underwent immunological and genetic assays. Their parents and ten healthy adults served as controls for the DNA analysis.

RESULTS

All three children presented with recurrent episodes of hematuria and proteinuria, the youngest starting at age 5 months. One child currently has nephrotic syndrome and end-stage renal disease. All of the children were found to be homozygous for a C.262C > A (p.Pro88Thr) mutation in exon 3 of CFH that is associated with a quantitative/functional deficiency of factor H. The parents of the three siblings were found to be heterozygous for the mutation. None of the controls carried this mutation.

CONCLUSIONS

Different mutations in CFH may be responsible for different glomerular diseases, including MPGN type I. A modifier gene or an environmental trigger may contribute to this phenotype-genotype discrepancy. Understanding the role of the alternative complement pathway in this disease would allow us to offer these patients more targeted therapy, including a clinical trial of eculizumab.

Successful therapy of C3Nef-positive C3 glomerulopathy with plasma therapy and immunosuppression

BACKGROUND

C3 glomerulopathies (C3G) are characterized by uncontrolled activation of the alternative pathway of complement. In most patients these diseases progress towards end-stage renal disease, and the risk of recurrence after renal transplantation is high. In the majority of patients, only antibodies against the C3 convertase, termed C3Nef, can be found as a potential pathogenic factor. Although a large variety of therapeutic approaches have been used, no generally accepted therapy exists.

METHODS

In four consecutive patients with C3G in whom all known complement factor mutations were excluded and only C3Nef could be identified as a potential cause of disease, a multimodal therapeutic regimen with plasma therapy, corticosteroids and mycophenolate mofetil was used.

RESULTS

The multimodal regimen achieved normalization of renal function in all four patients, with complete remission in two patients and a distinct reduction of proteinuria in the other two patients. The single patient with C3 glomerulonephritis (C3GN) and marked terminal complement complex elevation only showed partial remission; further improvement was achieved following the addition of eculizumab to the therapeutic regimen. Repeatedly measured C3Nef levels did not correlate with disease course or therapeutic response in any of the patients.

CONCLUSIONS

As this multimodal therapeutic approach was effective in all four treated patients with suspected autoimmune etiology of C3G, it offers a treatment option for severely affected patients with this rare disease until more specific regimens are available.

Complement Activation in Patients with Focal Segmental Glomerulosclerosis

Background

Recent pre-clinical studies have shown that complement activation contributes to glomerular and tubular injury in experimental FSGS. Although complement proteins are detected in the glomeruli of some patients with FSGS, it is not known whether this is due to complement activation or whether the proteins are simply trapped in sclerotic glomeruli. We measured complement activation fragments in the plasma and urine of patients with primary FSGS to determine whether complement activation is part of the disease process.

Study Design

Plasma and urine samples from patients with biopsy-proven FSGS who participated in the FSGS Clinical Trial were analyzed.

Setting and Participants

We identified 19 patients for whom samples were available from weeks 0, 26, 52 and 78. The results for these FSGS patients were compared to results in samples from 10 healthy controls, 10 patients with chronic kidney disease (CKD), 20 patients with vasculitis, and 23 patients with lupus nephritis.

Outcomes

Longitudinal control of proteinuria and estimated glomerular filtration rate (eGFR).

Measurements

Levels of the complement fragments Ba, Bb, C4a, and sC5b-9 in plasma and urine.

Results

Plasma and urine Ba, C4a, sC5b-9 were significantly higher in FSGS patients at the time of diagnosis than in the control groups. Plasma Ba levels inversely correlated with the eGFR at the time of diagnosis and at the end of the study. Plasma and urine Ba levels at the end of the study positively correlated with the level of proteinuria, the primary outcome of the study.

Limitations

Limited number of patients with samples from all time-points.

Conclusions

The complement system is activated in patients with primary FSGS, and elevated levels of plasma Ba correlate with more severe disease. Measurement of complement fragments may identify a subset of patients in whom the complement system is activated. Further investigations are needed to confirm our findings and to determine the prognostic significance of complement activation in patients with FSGS.

Eculizumab in Pediatric Dense Deposit Disease

BACKGROUND AND OBJECTIVES

Dense deposit disease (DDD), a subtype of C3 glomerulopathy, is a rare disease affecting mostly children. Treatment options are limited. Debate exists whether eculizumab, a monoclonal antibody against complement factor C5, is effective in DDD. Reported data are scarce, especially in children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The authors analyzed clinical and histologic data of five pediatric patients with a native kidney biopsy diagnosis of DDD. Patients received eculizumab as therapy of last resort for severe nephritic or nephrotic syndrome with alternative pathway complement activation; this therapy was given only when the patients had not or only marginally responded to immunosuppressive therapy. Outcome measures were kidney function, proteinuria, and urine analysis.

RESULTS

In all, seven disease episodes were treated with eculizumab (six episodes of severe nephritic syndrome [two of which required dialysis] and one nephrotic syndrome episode). Median age at treatment start was 8.4 (range, 5.9-13) years. For three treatment episodes, eculizumab was the sole immunosuppressive treatment. In all patients, both proteinuria and renal function improved significantly within 12 weeks of treatment (median urinary protein-to-creatinine ratio of 8.5 [range, 2.2-17] versus 1.1 [range, 0.2-2.0] g/g, P<0.005, and eGFR of 58 [range, 17-114] versus 77 [range, 50-129] ml/min per 1.73 m(2), P<0.01). A striking finding was the disappearance of leukocyturia within 1 week after the first eculizumab dose in all five episodes with leukocyturia at treatment initiation.

CONCLUSIONS

In this case series of pediatric patients with DDD, eculizumab treatment was associated with reduction in proteinuria and increase in eGFR. Leukocyturia resolved within 1 week of initiation of eculizumab treatment. These results underscore the need for a randomized trial of eculizumab in DDD.

Kidney Disease Caused by Dysregulation of the Complement Alternative Pathway: An Etiologic Approach

Kidney diseases caused by genetic or acquired dysregulation of the complement alternative pathway (AP) are traditionally classified on the basis of clinical presentation (atypical hemolytic uremic syndrome as thrombotic microangiopathy), biopsy appearance (dense deposit disease and C3 GN), or clinical course (atypical postinfectious GN). Each is characterized by an inappropriate activation of the AP, eventuating in renal damage. The clinical diversity of these disorders highlights important differences in the triggers, the sites and intensity of involvement, and the outcome of the AP dysregulation. Nevertheless, we contend that these diseases should be grouped as disorders of the AP and classified on an etiologic basis. In this review, we define different pathophysiologic categories of AP dysfunction. The precise identification of the underlying abnormality is the key to predict the response to immune suppression, plasma infusion, and complement-inhibitory drugs and the outcome after transplantation. In a patient with presumed dysregulation of the AP, the collaboration of the clinician, the renal pathologist, and the biochemical and genetic laboratory is very much encouraged, because this enables the elucidation of both the underlying pathogenesis and the optimal therapeutic approach.

Efficacy of Targeted Complement Inhibition in Experimental C3 Glomerulopathy

C3 glomerulopathy refers to renal disorders characterized by abnormal accumulation of C3 within the kidney, commonly along the glomerular basement membrane (GBM). C3 glomerulopathy is associated with complement alternative pathway dysregulation, which includes functional defects in complement regulator factor H (FH). There is no effective treatment for C3 glomerulopathy. We investigated the efficacy of a recombinant mouse protein composed of domains from complement receptor 2 (CR2) and FH (CR2-FH) in two models of C3 glomerulopathy with either preexisting or triggered C3 deposition along the GBM. FH-deficient mice spontaneously develop renal pathology associated with abnormal C3 accumulation along the GBM and secondary plasma C3 deficiency. CR2-FH partially restored plasma C3 levels in FH-deficient mice 2 hours after intravenous injection. CR2-FH specifically targeted glomerular C3 deposits, reduced the linear C3 reactivity assessed with anti-C3 and anti-C3b/iC3b/C3c antibodies, and prevented further spontaneous accumulation of C3 fragments along the GBM. Reduction in glomerular C3d and C9/C5b-9 reactivity was observed after daily administration of CR2-FH for 1 week. In a second mouse model with combined deficiency of FH and complement factor I, CR2-FH prevented de novo C3 deposition along the GBM. These data show that CR2-FH protects the GBM from both spontaneous and triggered C3 deposition in vivo and indicate that this approach should be tested in C3 glomerulopathy.

A case of C3 glomerulonephritis successfully treated with eculizumab

BACKGROUND

C3 glomerulonephritis (C3GN) is a rare form of glomerulopathy that is characterized by predominant C3 deposits. Eculizumab, a humanized monoclonal C5 antibody, has recently emerged as a treatment option for C3GN. We report a C3GN patient successfully treated with eculizumab.

CASE DIAGNOSIS/TREATMENT

A 5-year-old boy who presented with proteinuria, hematuria, high ASO titers, and low C3 levels was initially diagnosed with post-streptococcal GN. His first kidney biopsy confirmed this diagnosis, but complement investigations identified three alternative pathway dysregulation factors: C3 nephritic factor, complement factor I heterozygous mutation (I398L), and anti-factor H autoantibodies (4,500 AU/ml). A second biopsy performed 11 months after initial presentation (nephrotic range proteinuria) showed a C3GN suggestive of isolated C3 deposits. Despite the use of intensive immunosuppressive therapy (rituximab, corticosteroids, mycophenolate), nephrotic-range proteinuria persisted and a third kidney biopsy showed the same C3GN pattern with more endocapillary proliferation. The serum C5b-9 level was elevated. Eculizumab was initiated and resulted in a significant decline of proteinuria (5.3 to 1.3 g/day) and an improvement in pathologic features. A transient interruption of eculizumab resulted in a rapid rise in proteinuria to 9.3 g/day, which decreased to 0.8 g/day after resumption of treatment.

CONCLUSIONS

The administration of anti-C5 antibodies may represent a valuable therapeutic option in patients with C3GN.

Complement involvement in kidney diseases: From physiopathology to therapeutical targeting

Complement cascade is involved in several renal diseases and in renal transplantation. The different components of the complement cascade might represent an optimal target for innovative therapies. In the first section of the paper the authors review the physiopathology of complement involvement in renal diseases and transplantation. In some cases this led to a reclassification of renal diseases moving from a histopathological to a physiopathological classification. The principal issues afforded are: renal diseases with complement over activation, renal diseases with complement dysregulation, progression of renal diseases and renal transplantation. In the second section the authors discuss the several complement components that could represent a therapeutic target. Even if only the anti C5 monoclonal antibody is on the market, many targets as C1, C3, C5a and C5aR are the object of national or international trials. In addition, many molecules proved to be effective in vitro or in preclinical trials and are waiting to move to human trials in the future.

Compstatin analog Cp40 inhibits complement dysregulation in vitro in C3 glomerulopathy

C3 glomerulopathy (C3G) defines a group of untreatable ultra-rare renal diseases caused by uncontrolled activation of the alternative complement pathway. Nearly half of patients progress to end stage renal failure within 10 years. Cp40, a second-generation compstatin analog in clinical development, is a 14 amino-acid cyclic peptide that selectively inhibits complement activation in humans and non-human primates by binding to C3 and C3b. We hypothesized that by targeting C3 Cp40 would provide an effective treatment for C3G. By investigating its effects in vitro using multiple assays of complement activity, we show that Cp40 prevents complement-mediated lysis of sheep erythrocytes in sera from C3G patients, prevents complement dysregulation in the presence of patient-derived autoantibodies to the C3 and C5 convertases, and prevents complement dysregulation associated with disease-causing genetic mutations. In aggregate, these data suggest that Cp40 may offer a novel and promising therapeutic option to C3G patients as a disease-specific, targeted therapy. As such, Cp40 could represent a major advance in the treatment of this disease.

Advances in the understanding of complement mediated glomerular disease: implications for recurrence in the transplant setting

Recent advances in the understanding of the role of complement in glomerular disease allow for more accurate assessment of the risk of disease recurrence after transplantation, and inform the development of targeted treatment strategies to overcome specific defects in the alternate pathway of the complement system. These advances along with remaining knowledge deficits are reviewed with specific relevance to membranoproliferative glomerulonephritis (MPGN) and C3 glomerulopathy, a heterogenous group of diseases with a high rate of recurrence leading to allograft failure. Recommendations to establish an accurate diagnosis and inform therapeutic decision making in transplant candidates with a histologic diagnosis of MPGN are provided.

Molecules Great and Small: The Complement System

The complement cascade, traditionally considered an effector arm of innate immunity required for host defense against pathogens, is now recognized as a crucial pathogenic mediator of various kidney diseases. Complement components produced by the liver and circulating in the plasma undergo activation through the classical and/or mannose-binding lectin pathways to mediate anti-HLA antibody-initiated kidney transplant rejection and autoantibody-initiated GN, the latter including membranous glomerulopathy, antiglomerular basement membrane disease, and lupus nephritis. Inherited and/or acquired abnormalities of complement regulators, which requisitely limit restraint on alternative pathway complement activation, contribute to the pathogenesis of the C3 nephropathies and atypical hemolytic uremic syndrome. Increasing evidence links complement produced by endothelial cells and/or tubular cells to the pathogenesis of kidney ischemia-reperfusion injury and progressive kidney fibrosis. Data emerging since the mid-2000s additionally show that immune cells, including T cells and antigen-presenting cells, produce alternative pathway complement components during cognate interactions. The subsequent local complement activation yields production of the anaphylatoxins C3a and C5a, which bind to their respective receptors (C3aR and C5aR) on both partners to augment effector T-cell proliferation and survival, while simultaneously inhibiting regulatory T-cell induction and function. This immune cell-derived complement enhances pathogenic alloreactive T-cell immunity that results in transplant rejection and likely contributes to the pathogenesis of other T cell-mediated kidney diseases. C5a/C5aR ligations on neutrophils have additionally been shown to contribute to vascular inflammation in models of ANCA-mediated renal vasculitis. New translational immunology efforts along with the development of pharmacologic agents that block human complement components and receptors now permit testing of the intriguing concept that targeting complement in patients with an assortment of kidney diseases has the potential to abrogate disease progression and improve patient health.

Eculizumab for treatment of rapidly progressive C3 glomerulopathy

C3 glomerulopathy (C3G) is a prototypic complement-mediated kidney disease. Rapidly progressive forms of C3G usually respond poorly to conventional treatments. We report on the efficacy of the terminal complement inhibitor eculizumab in 3 adult patients with rapidly progressive C3G. In all 3 patients, serum creatinine levels had increased by >50% in the 2 months preceding initiation of eculizumab treatment despite the use of conventional immunosuppressive drugs and/or plasma exchanges in 2 of these individuals. Of note, 2 patients had long-standing nephrotic syndrome. Kidney biopsy performed prior to eculizumab treatment disclosed marked glomerular inflammatory changes and increased C5b-9 deposition in all patients. Eculizumab use was associated with significant improvement in kidney function, with estimated glomerular filtration rates of patients increasing 22 to 38 mL/min/1.73 m(2). Eculizumab use also was associated with remission of nephrotic syndrome in the 2 affected patients, an effect observed as early as one week after treatment initiation. Repeat kidney biopsy disclosed regression of glomerular inflammatory changes and decreases in glomerular staining for C5b-9 in all patients. These results warrant further assessment of eculizumab for treatment of rapidly progressive forms of C3G with markedly increased glomerular C5b-9 deposits.

Eculizumab in the treatment of membranoproliferative glomerulonephritis

A major shift in our understanding of the membranoproliferative glomerulonephritis (MPGN) lesion is the focus on which components of the complement pathway are involved in mediating renal injury. Hence, MPGN is no longer classified solely by ultrastructural findings on biopsy but instead divided into immune complex-mediated lesions versus complement-mediated lesions. This emphasis on complement, in turn, leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anticomplement therapy, blocks at the level of C5 and has revolutionized the treatment of complement-mediated diseases such as paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous complement-mediated MPGN lesions, also known as C3 glomerulopathy, remains unclear. To date, the experience and published data on using eculizumab in MPGN suggests this agent will work for some, but not all, patients with this pathologic lesion.

Update on C3 glomerulopathy

C3 glomerulopathy refers to a disease process in which abnormal control of complement activation, degradation or deposition results in predominant C3 fragment deposition within the glomerulus and glomerular damage. Recent studies have improved our understanding of its pathogenesis. The key abnormality is uncontrolled C3b amplification in the circulation and/or along the glomerular basement membrane. Family studies in which disease segregates with structurally abnormal complement factor H-related (CFHR) proteins demonstrate that abnormal CFHR proteins are important in some types of C3 glomerulopathy. This is currently thought to be due to the ability of these proteins to antagonize the major negative regulator of C3 activation, complement factor H (CFH), a process termed ‘CFH de-regulation’. Recent clinicopathological cohort studies have led to further refinements in case definition, culminating in a 2013 consensus report, which provides recommendations regarding investigation and treatment. Early clinical experience with complement-targeted therapeutics, notably C5 inhibitors, has also now been published. Here, we summarize the latest developments in C3 glomerulopathy.

Eculizumab in dense-deposit disease after renal transplantation

BACKGROUND

Dense-deposit disease (DDD) is a rare glomerulopathy characterized by electron-dense deposits in the glomerular basement membrane. About 50 % of patients with DDD progress to end-stage kidney disease and require dialysis within 10 years of diagnosis, and the disease often recurs after renal transplantation.

CASE-DIAGNOSIS/TREATMENT

We describe a 14-year-old girl with recurrent DDD in her transplanted kidney. Clinical onset was at 8 years of age, when steroid-resistant nephrotic syndrome was diagnosed with microhematuria, severe hypocomplementemia and normal kidney function. Although remission was initially observed after several plasma exchanges, nephrotic proteinuria returned and kidney function further declined 1 year later. The patient received a living-related kidney transplant. Initial allograft function was good, but proteinuria reappeared 3 months after transplantation, accompanied by a slight deterioration in kidney function. After histological confirmation of DDD recurrence and subsequent management with plasmapheresis, the patient was treated for 30 months with eculizumab, a humanized monoclonal antibody that binds to C5 complement protein. This intervention proved effective and resulted in complement inhibition, sustained remission of proteinuria and preservation of renal function. A graft biopsy 6 months later showed no progression of the renal lesions.

CONCLUSIONS

Early clinical and histological recurrence of DDD in the transplanted kidney in this 14-year-old patient was treated for 30 months with eculizumab. The patient remains asymptomatic, has no proteinuria and her kidney function is intact.

Mass spectrometry based proteomics in the diagnosis of kidney disease

PURPOSE OF REVIEW

Laser microdissection (LMD) and mass spectrometry (MS) is a new technique that consists of dissection of glomeruli, tryptic digestion of dissected material, analysis by MS and generation of a protein profile using different algorithms. The review focuses on the use of this methodology as an ancillary technique in a clinical laboratory for the diagnosis of kidney diseases.

RECENT FINDINGS

LMD/MS is used in the diagnosis and typing of kidney diseases with organized deposits such as amyloidosis. Uncommon and familial forms of renal amyloidosis are diagnosed and typed on the basis of the presence of specific amyloidogenic proteins. LMD/MS is used to confirm and identify immunoglobulins and complement factors in immune complex mediated and complement-mediated proliferative glomerulonephritis, respectively. In particular, LMD/MS can detect monoclonal immunoglobulins in cases of equivocal immunofluorescence studies in monoclonal immunoglobulins-associated glomerulonephritis. LMD/MS can detect specific complement factors of the alternative pathway and terminal pathway in complement-mediated glomerulonephritis.

SUMMARY

LMD/MS is currently used for diagnosis and typing of amyloidosis. In addition, LMD/MS is useful in determining the type of immunoglobulins and complement factors in immune complex and complement-mediated glomerulonephritis, respectively.

Eculizumab therapy in a patient with dense-deposit disease associated with partial lipodystropy

BACKGROUND

Dense deposit disease (DDD) (also known as membranoproliferative glomerulonephritis type II) in childhood is a rare glomerulonephritis with frequent progression to end-stage renal disease (ESRD) and a high recurrence after kidney transplantation. The pathophysiologic basis of DDD is associated with the uncontrolled systemic activation of the alternative pathway (AP) of the complement cascade.

CASE-DIAGNOSIS/TREATMENT

A 14-year-old girl presented with edema and nephrotic range proteinuria. Blood tests showed hypoalbuminemia, nephrotic range proteinuria, normal renal function, and a low C3 level. Renal biopsy confirmed the diagnosis of crescentic DDD. Complement analysis revealed strong AP activation (low C3), positive C3 nephritic factor (C3NeF), and a decreased complement factor H (CFH) levels with CFH polymorphisms. Therapy with eculizumab was considered after the failure of corticosteroid and plasmapheresis to modulate the ongoing massive proteinuria and persistence of low serum C3 levels. There was a marked clinical and biochemical response following the administration of eculizumab.

CONCLUSIONS

Our case emphasizes the efficacy of eculizumab in the management of crescentic DDD in a patient with a normal renal function, in a short follow-up period. Considering previously reported cases, it appears that eculizumab represents a promising new approach which may prevent progression to ESRD in a subset of patients with DDD.

Rituximab fails where eculizumab restores renal function in C3nef-related DDD

BACKGROUND

Dense deposit disease (DDD), a C3 glomerulopathy (C3G), is a rare disease with unfavorable progression towards end-stage kidney disease. The pathogenesis of DDD is due to cytotoxic effects related to acquired or genetic dysregulation of the complement alternative pathway, which is at times accompanied by the production of C3 nephritic factor (C3NeF), an auto-antibody directed against the alternative C3 convertase. Available treatments include plasma exchange, CD20-targeted antibodies, and a terminal complement blockade via the anti-C5 monoclonal antibody eculizumab.

CASE-DIAGNOSIS/TREATMENT

We report here the case of an 8-year-old child with C3NeF and refractory DDD who presented with a nephritic syndrome. She tested positive for C3NeF activity; C3 was undetectable. Genetic analyses of the alternative complement pathway were normal. Methylprednisolone pulses and mycophenolate mofetil treatment resulted in complete recovery of renal function and a reduction in proteinuria. Corticosteroids were tapered and then withdrawn. Four months after corticosteroid discontinuation, hematuria and proteinuria recurred, and a renal biopsy confirmed an active DDD with a majority of extracapillary crescents. Despite an increase in immunosuppressive drugs, including methylprednisolone pulses and rituximab therapy, the patient suffered acute renal failure within 3 weeks, requiring dialysis. Eculizumab treatment resulted in a quick and impressive response. Hematuria very quickly resolved, kidney function improved, and no further dialysis was required. The patient received bimonthly eculizumab injections of 600 mg, allowing for normalization of renal function and reduction of proteinuria to <0.5 g per day. Since then, she continues to receive eculizumab.

CONCLUSION

Complement regulation pathway-targeted therapy may be a specific and useful treatment for rapidly progressing DDD prior to the development of glomerulosclerosis. Our data provide evidence supporting the pivotal role of complement alternative pathway abnormalities in C3G with DDD.

American Society of Nephrology clinical pathological conference

A 13-year-old girl presented with proteinuria and acute kidney failure. She was born at full term via cesarean delivery (due to nuchal cord), but there were no other prenatal or perinatal complications. In early childhood the patient had two hospitalizations at ages 4.5 and 9 years, respectively, the latter for pneumonia. She had no history of symptoms of kidney disease. She came to the hospital at age 12 years for routine bilateral molar extractions. She was treated with oral antibiotics and discharged after the procedure without complications. At age 13 years, 10 months after the molar extraction, she was seen by a pediatrician because of puffiness and increased BP. She had had respiratory symptoms 2 weeks before presentation. The pediatrician prescribed furosemide and amlodipine. A few days later, the patient returned to the pediatrician's office because of hand, ankle, and facial swelling and malaise. The pediatrician recommended hospitalization and the patient was admitted at this time.

Anti-complement therapy for glomerular diseases

A major shift in our understanding of glomerular diseases is the focus on which components of the complement pathway are involved in mediating kidney injury. For example, the membranoproliferative glomerulonephritis lesion is no longer classified solely by ultrastructural findings on biopsy and is now divided into immune-complex-mediated lesions vs complement-mediated lesions. In turn, this emphasis on complement leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anti-complement therapy, blocks at the level of C5 and has revolutionized the treatment of atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous entities of C3 glomerulonephritis and dense deposit disease remains unclear. Instead, newer agents that target C3 may turn out to be the most effective and specific therapy for these C3 glomerulopathies.

[C3 glomerulopathy]

C3 glomerulopathy is an heterogeneous group of glomerular diseases associated with acquired or genetic abnormalities of complement alternative pathway (AP) components. It is characterized by predominant C3 deposits in the mesangium and along the glomerular basement membrane (GBM). Presenting features comprise proteinuria (sometimes with nephritic syndrome), haematuria, hypertension and renal failure. C3 glomerulopathy have a poor renal prognosis with progression to end stage renal disease (ESRD) in 50% of cases during the first decade after initial presentation. Moreover, C3 deposits recur in most of cases after renal transplantation. Patients frequently have low serum C3 level attributed to the activation of the alternative pathway of complement. Animal models have confirmed the role of excessive C3 activation in the pathogenesis of C3 glomerulopathy. To date, the optimal treatment remains unknown. It is currently based on the use of angiotensin-converting-enzyme inhibitors (ACEI) and angiotensin II-receptor blockers (ARB), sometimes associated with immunosuppressive therapy. Blockade of C5a release with eculizumab, a monoclonal anti-C5 antibody, may be of particular interest in the treatment of C3G.

Blockade of alternative complement pathway in dense deposit disease

A patient aged 17 with dense deposit disease associated with complement activation, circulating C3 Nef, and Factor H mutation presented with nephrotic syndrome and hypertension. Steroid therapy, plasma exchange, and rituximab failed to improve proteinuria and hypertension despite a normalization of the circulating sC5b9 complex. Eculizumab, a monoclonal antibody directed against C5, was used to block the terminal product of the complement cascade. The dose was adapted to achieve a CH50 below 10%, but proteinuria and blood pressure were not improved after 3 months of treatment.

The expanding role of therapeutic antibodies

Therapeutic antibodies have been used since the end of nineteenth century, but their use is progressively increased and recently, with the availability of monoclonal antibodies, they are successfully employed in a large disease spectrum, which transversally covers different fields of medicine. Hyperimmune polyclonal immune globulin has been used against infectious diseases, in a period in which anti-microbial drugs were not yet available, and it still maintains a relevant place in prophylaxis/therapy. Although immune globulin should be considered life-saving as replacement therapy in humoral immunodeficiencies, its place in the immune-modulating treatment is not usually first-choice, but it should be considered as support to standard approved treatments. Despite therapeutic monoclonal antibodies have been lastly introduced in therapy, their extreme potentiality is reflected by the large number of approved molecules, addressed toward different immunological targets and able to heavily influence the prognosis and quality of life of a wide range of different diseases.

Update on membranoproliferative GN

Membranoproliferative GN represents a pattern of injury seen on light microscopy. Historically, findings on electron microscopy have been used to further subclassify this pathologic entity. Recent advances in understanding of the underlying pathobiology have led to a proposed classification scheme based on immunofluorescence findings. Dysregulation of the complement system has been shown to be a major risk factor for the development of a membranoproliferative GN pattern of injury on kidney biopsy. Evaluation and treatment of this complex disorder rest on defining the underlying mechanisms.

Novel use of intravenous immunoglobulin G in complement factor H missense mutation: a case report

A white girl presented at 8 months of age with thrombotic microangiopathy, followed by recurrent episodes of renal dysfunction, hemolysis, and thrombocytopenia, compatible with atypical hemolytic uremic syndrome. The episodes of the syndrome were treated by a combination of infusions of fresh frozen plasma, plasmapheresis, and continuous venovenous hemodialysis. Interval resolution occurred between episodes. At 2 years of age, prophylactic infusions of fresh frozen plasma were started between relapses, but this proved to be poorly protective; however, introduction of prophylactic intravenous gamma globulin at age 3.5 years resulted in prolonged remission (42 months). Serum levels of the third and fourth components of complement, total hemolytic complement, and complement factor H were normal. Results of the third component functional assay were low before and normalized after the start of immunoglobulin G prophylaxis. A missense mutation of complement factor H was identified. At 6 years of age, the patient underwent bilateral native nephrectomy and started long-term peritoneal dialysis, followed by a combined liver-kidney transplant at age 8 years. Four and a half years after transplant, she has excellent renal and liver graft function without recurrence of atypical hemolytic uremic syndrome.

Complement factor H-related hybrid protein deregulates complement in dense deposit disease

The renal disorder C3 glomerulopathy with dense deposit disease (C3G-DDD) pattern results from complement dysfunction and primarily affects children and young adults. There is no effective treatment, and patients often progress to end-stage renal failure. A small fraction of C3G-DDD cases linked to factor H or C3 gene mutations as well as autoantibodies have been reported. Here, we examined an index family with 2 patients with C3G-DDD and identified a chromosomal deletion in the complement factor H-related (CFHR) gene cluster. This deletion resulted in expression of a hybrid CFHR2-CFHR5 plasma protein. The recombinant hybrid protein stabilized the C3 convertase and reduced factor H-mediated convertase decay. One patient was refractory to plasma replacement and exchange therapy, as evidenced by the hybrid protein quickly returning to pretreatment plasma levels. Subsequently, complement inhibitors were tested on serum from the patient for their ability to block activity of CFHR2-CFHR5. Soluble CR1 restored defective C3 convertase regulation; however, neither eculizumab nor tagged compstatin had any effect. Our findings provide insight into the importance of CFHR proteins for C3 convertase regulation and identify a genetic variation in the CFHR gene cluster that promotes C3G-DDD. Monitoring copy number and sequence variations in the CFHR gene cluster in C3G-DDD and kidney patients with C3G-DDD variations will help guide treatment strategies.

Dense deposit disease and C3 glomerulopathy

C3 glomerulopathy refers to those renal lesions characterized histologically by predominant C3 accumulation within the glomerulus, and pathogenetically by aberrant regulation of the alternative pathway of complement. Dense deposit disease is distinguished from other forms of C3 glomerulopathy by its characteristic appearance on electron microscopy. The extent to which dense deposit disease also differs from other forms of C3 glomerulopathy in terms of clinical features, natural history, and outcomes of treatment including renal transplantation is less clear. We discuss the pathophysiology of C3 glomerulopathy, with evidence for alternative pathway dysregulation obtained from affected individuals and complement factor H (Cfh)-deficient animal models. Recent linkage studies in familial C3 glomerulopathy have shown genomic rearrangements in the Cfh-related genes, for which the novel pathophysiologic concept of Cfh deregulation has been proposed.

C3 glomerulopathy: clinicopathologic features and predictors of outcome

BACKGROUND AND OBJECTIVES

The term C3 glomerulopathy describes renal disorders characterized by the presence of glomerular deposits composed of C3 in the absence of significant amounts of Ig. On the basis of electron microscopy appearance, subsets of C3 glomerulopathy include dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). The full spectrum of histologic change observed in C3 glomerulopathy has yet to be defined and pathologic predictors of renal outcome within this patient population remain largely unknown. This study thus characterized a large C3 glomerulopathy cohort and identified clinicopathologic predictors of renal outcome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

All patients with kidney biopsies fulfilling criteria for C3 glomerulopathy from two quaternary renal centers within the United Kingdom and Ireland between 1992 and 2012 were retrospectively reviewed. We recorded histologic, demographic, and clinical data and determined predictors of ESRD using the Cox proportional hazards model.

RESULTS

Eighty patients with C3 glomerulopathy were identified: 21 with DDD and 59 with C3GN. Patients with DDD were younger, more likely to have low serum C3 levels, and more likely to have crescentic GN than patients with C3GN. Patients with C3GN were older and had more severe arteriolar sclerosis, glomerular sclerosis, and interstitial scarring than patients with DDD. Of 70 patients with available follow-up data, 20 (29%) progressed to ESRD after a median of 28 months. Age >16 years, DDD subtype, and crescentic GN were independent predictors of ESRD within the entire cohort. Renal impairment at presentation predicted ESRD only among patients with DDD.

CONCLUSIONS

Although detailed serologic and genetic data are lacking, this study nevertheless identifies important clinicopathologic distinctions between patients with DDD and C3GN. These include independent predictors of renal outcome. If replicated in other cohorts, these predictors could be used to stratify patients, enabling application of emerging mechanism-based therapies to patients at high risk for poor renal outcome.

C3 glomerulopathy: consensus report

C3 glomerulopathy is a recently introduced pathological entity whose original definition was glomerular pathology characterized by C3 accumulation with absent or scanty immunoglobulin deposition. In August 2012, an invited group of experts (comprising the authors of this document) in renal pathology, nephrology, complement biology, and complement therapeutics met to discuss C3 glomerulopathy in the first C3 Glomerulopathy Meeting. The objectives were to reach a consensus on: the definition of C3 glomerulopathy, appropriate complement investigations that should be performed in these patients, and how complement therapeutics should be explored in the condition. This meeting report represents the current consensus view of the group.

Eculizumab and recurrent C3 glomerulonephritis

BACKGROUND

Hyperactivity of the alternative complement pathway is the principle defect in C3 glomerulopathies (C3G). Eculizumab, a monoclonal antibody that binds C5 to prevent formation of the membrane attack complex, has been shown to be beneficial in some patients with this disease.

METHODS

In this open-label, proof-of-concept efficacy-and-safety study, a patient with the initial diagnosis of dense deposit disease (DDD) and allograft recurrence of C3 glomerulonephritis (C3GN) was treated with eculizumab every other week for 1 year. The patient had pathological evidence of C3GN and proteinuria >1 g/day at enrollment. He underwent graft biopsy before enrollment and repeat biopsy at 6 and 12 months.

RESULTS

Although no mutations were identified in complement genes, functional studies were positive for C3 nephritic factors and elevated levels of soluble membrane attack complex (sMAC). On therapy, sMAC levels normalized and although proteinuria initially decreased, it increased reaching pre-treatment levels at 12 months. Although serum creatinine remained stable, repeat allograft biopsies showed progression of disease.

CONCLUSIONS

Clinical and histopathologic data suggest a partial response to eculizumab in this patient. While eculizumab blocked activation of the terminal complement cascade, persistent dysregulation of the alternative pathway remained, indicating eculizumab alone cannot control disease in this patient. Additional research is required to identify effective anticomplement therapy for this group of C3G patients.

The immune system and kidney disease: basic concepts and clinical implications

The kidneys are frequently targeted by pathogenic immune responses against renal autoantigens or by local manifestations of systemic autoimmunity. Recent studies in rodent models and humans have uncovered several underlying mechanisms that can be used to explain the previously enigmatic immunopathology of many kidney diseases. These mechanisms include kidney-specific damage-associated molecular patterns that cause sterile inflammation, the crosstalk between renal dendritic cells and T cells, the development of kidney-targeting autoantibodies and molecular mimicry with microbial pathogens. Conversely, kidney failure affects general immunity, causing intestinal barrier dysfunction, systemic inflammation and immunodeficiency that contribute to the morbidity and mortality of patients with kidney disease. In this Review, we summarize the recent findings regarding the interactions between the kidneys and the immune system.

C3 glomerulopathy-associated CFHR1 mutation alters FHR oligomerization and complement regulation

C3 glomerulopathies (C3G) are a group of severe renal diseases with distinct patterns of glomerular inflammation and C3 deposition caused by complement dysregulation. Here we report the identification of a familial C3G-associated genomic mutation in the gene complement factor H–related 1 (CFHR1), which encodes FHR1. The mutation resulted in the duplication of the N-terminal short consensus repeats (SCRs) that are conserved in FHR2 and FHR5. We determined that native FHR1, FHR2, and FHR5 circulate in plasma as homo- and hetero-oligomeric complexes, the formation of which is likely mediated by the conserved N-terminal domain. In mutant FHR1, duplication of the N-terminal domain resulted in the formation of unusually large multimeric FHR complexes that exhibited increased avidity for the FHR1 ligands C3b, iC3b, and C3dg and enhanced competition with complement factor H (FH) in surface plasmon resonance (SPR) studies and hemolytic assays. These data revealed that FHR1, FHR2, and FHR5 organize a combinatorial repertoire of oligomeric complexes and demonstrated that changes in FHR oligomerization influence the regulation of complement activation. In summary, our identification and characterization of a unique CFHR1 mutation provides insights into the biology of the FHRs and contributes to our understanding of the pathogenic mechanisms underlying C3G.

Primary glomerulonephritis: A review of important recent discoveries

The publication of the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines on the treatment of glomerular diseases in 2012 marked a milestone in this field, as it is the first time that comprehensive guidelines are provided for such disease entities. The current review focuses on major findings, both pathogenesis related and clinical, in the primary glomerulonephritis that have been made after the guidelines came into effect.

Treatment options for C3 glomerulopathy

PURPOSE OF REVIEW

The purpose of this review is to discuss emerging nomenclature, review the salient clinicopathological features and describe the therapeutic options available for the treatment of C3 glomerulopathy (C3G).

RECENT FINDINGS

C3G is minimally responsive to traditional immune suppression and randomized controlled trials to support therapy are absent. The burgeoning understanding of the role of the alternative complement pathway in C3G combined with animal data supporting the use of terminal complement blockade and a few reports suggesting that the anticomplement drug eculizumab may offer a therapeutic advantage have triggered great interest in the field of complement-mediated renal disease.

SUMMARY

Anticellular immune suppression and plasma therapy have limited efficacy in C3G. Data suggest that eculizumab may ameliorate disease in some C3G patients. The limited, recently published cohort data highlight crucial aspects of this group of diseases and support the need for extensive genetic and biomarker research to validate the pathologic mechanisms, delineate the spectrum of disease and guide the design of the rigorous trials to identify effective therapies for the treatment of C3G.

Novel roles of complement in renal diseases and their therapeutic consequences

The complement system functions as a part of the innate immune system. Inappropriate activation of the complement pathways has a deleterious effect on kidneys. Recent advances in complement research have provided new insights into the pathogenesis of glomerular and tubulointerstitial injury associated with complement activation. A new disease entity termed 'C3 glomerulopathy' has recently been proposed and is characterized by isolated C3 deposition in glomeruli without positive staining for immunoglobulins. Genetic and functional studies have demonstrated that several different mutations and disease variants, as well as the generation of autoantibodies, are potentially associated with its pathogenesis. The data from comprehensive analyses suggest that complement dysregulation can also be associated with hemolytic uremic syndrome and more common glomerular diseases, such as IgA nephropathy and diabetic kidney disease. In addition, animal studies utilizing genetically modified mice have begun to elucidate the molecular pathomechanisms associated with the complement system. From a diagnostic point of view, a noninvasive, MRI-based method for detecting C3 has recently been developed to serve as a novel tool for diagnosing complement-mediated kidney diseases. While novel therapeutic tools related to complement regulation are emerging, studies evaluating the precise roles of the complement system in kidney diseases will still be useful for developing new therapeutic approaches.

Eculizumab in the treatment of atypical haemolytic uraemic syndrome and other complement-mediated renal diseases

PURPOSE OF REVIEW

This review considers the use of eculizumab in the treatment of atypical haemolytic uraemic syndrome (aHUS) as well as the other complement-mediated renal diseases, including dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). In addition, a brief discussion of the effectiveness of eculizumab for the prevention of antibody-mediated rejection (AMR) in the setting of renal transplant and the treatment of shiga toxin associated haemolytic uraemic syndrome (STEC HUS) is also provided.

RECENT FINDINGS

No randomized controlled trials exist to support the use of eculizumab in renal disease. The results of two unpublished, prospective adult and adolescent trials support its utility in aHUS, whereas retrospective data support the effectiveness in paediatric aHUS. These two data sets form the basis of the sole renal indication for eculizumab. One small, single-centre trial and a growing number of case reports support the use of eculizumab in C3 glomerulopathy (C3G). There are limited trial data in AMR and renal transplant. Finally, there are conflicting data for the use of eculizumab in STEC HUS.

SUMMARY

The cumulative published data establish the effectiveness of eculizumab in a select group of renal diseases that have at the centre of their disease either abnormal complement control or maladaptive complement activation.

Complement dysregulation and disease: from genes and proteins to diagnostics and drugs

During the last decade, numerous studies have associated genetic variations in complement components and regulators with a number of chronic and infectious diseases. The functional characterization of these complement protein variants, in addition to recent structural advances in understanding of the assembly, activation and regulation of the AP C3 convertase, have provided important insights into the pathogenic mechanisms involved in some of these complement related disorders. This knowledge has identified potential targets for complement inhibitory therapies which are demonstrating efficacy and generating considerable expectation in changing the natural history of these diseases. Comprehensive understanding of the genetic and non-genetic risk factors contributing to these disorders will also result in targeting of the right patient groups in a stratified medicine approach through better diagnostics and individually tailored treatments, thereby improving management of patients.

Recent insights into C3 glomerulopathy

‘C3 glomerulopathy’ is a recent disease classification comprising several rare types of glomerulonephritis (GN), including dense deposit disease (DDD), C3 glomerulonephritis (C3GN) and CFHR5 nephropathy. These disorders share the key histological feature of isolated complement C3 deposits in the glomerulus. A common aetiology involving dysregulation of the alternative pathway (AP) of complement has been elucidated in the past decade, with genetic defects and/or autoantibodies able to be identified in a proportion of patients. We review the clinical and histological features of C3 glomerulopathy, relating these to underlying molecular mechanisms. The role of uncontrolled C3 activation in pathogenesis is emphasized, with important lessons from animal models. Methods, advantages and limitations of gene testing in the assessment of individuals or families with C3 glomerulopathy are discussed. While no therapy has yet been shown consistently effective, clinical evaluation of agents targeting specific components of the complement system is ongoing. However, limits to current knowledge regarding the natural history and the appropriate timing and duration of proposed therapies need to be addressed.

Alternative pathway dysfunction in kidney disease: a case report and review of dense deposit disease and C3 glomerulopathy

Dysfunction of the alternative pathway of complement activation provides a pathophysiologic link between the C3 glomerulopathies dense deposit disease and glomerulonephritis with C3 deposition and the clinically and histologically distinct atypical hemolytic uremic syndrome. Previously, dense deposit disease was known as membranoproliferative glomerulonephritis type II, but paucity or complete lack of immunoglobulin deposition on immunofluorescence staining and advances in our understanding of alternative pathway dysregulation have separated it from immune complex-mediated membranoproliferative glomerulonephritis types I and III. We discuss a case of dense deposit disease and review the current pathologic classification, clinical course, treatment options, and related conditions.

Kidney diseases caused by complement dysregulation: acquired, inherited, and still more to come

Inherited and acquired dysregulation of the complement alternative pathway plays an important role in multiple renal diseases. In recent years, the identification of disease-causing mutations and genetic variants in complement regulatory proteins has contributed significantly to our knowledge of the pathogenesis of complement associated glomerulopathies. In these diseases defective complement control leading to the deposition of activated complement products plays a key role. Consequently, complement-related glomerulopathies characterized by glomerular complement component 3 (C3) deposition in the absence of local immunoglobulin deposits are now collectively described by the term “C3 glomerulopathies.” Therapeutic strategies for reestablishing complement regulation by either complement blockade with the anti-C5 monoclonal antibody eculizumab or plasma substitution have been successful in several cases of C3 glomerulopathies. However, further elucidation of the underlying defects in the alternative complement pathway is awaited to develop pathogenesis-specific therapies.