Deletion of Lys224 in regulatory domain 4 of Factor H reveals a novel pathomechanism for dense deposit disease (MPGN II)

Chronic kidney disease enhances alternative pathway activity: a new paradigm

Reduced kidney function is associated with increased risk of cardiovascular disease in addition to kidney disease progression. Kidney disease is considered an inflammatory state, based on elevated levels of C-reactive protein and inflammatory cytokines. A key mediator of cardiovascular and kidney disease progression in the setting of reduced kidney function is systemic and vascular inflammation. However, the exact pathways that link chronic kidney disease (CKD) with inflammation remain incompletely understood. For decades it has been known that factor D, the main activator of the alternative complement pathway, is increased in the plasma of patients with reduced kidney function. Recent biomarker evidence suggests alternative pathway activation in this setting. CKD, therefore, seems to alter the balance of alternative pathway proteins, promoting inflammation and potentially exacerbating complement-mediated diseases and CKD-associated complications. In this manuscript, we review the impact of reduced kidney function on biomarkers of the alternative complement pathway and the implications of alternative pathway activation on cardiovascular disease and kidney disease progression. Importantly, we highlight the need for ongoing research efforts that may lead to opportunities to target the alternative pathway of complement withx the goal of improving kidney and cardiovascular outcomes in persons with reduced kidney function.

Truncated complement factor H Y402 gene therapy rescues C3 glomerulonephritis

There are no effective therapies for patients with dry age-related macular degeneration (AMD) or C3 glomerulonephritis (C3G). Unfortunately, past efforts to treat C3G using exogenous human complement factor H (CFH) found limited success due to immune rejection of a foreign protein response. AMD research has also faced myriad challenges, including the absence of an ideal therapeutic target and difficulties with treatment delivery in certain preclinical models. In pursuit of an AMD therapy to overcome these obstacles, we ultimately capitalized on parallels in complement dysregulation between AMD and C3G. Here, we investigate the potential for CFH supplementation as a strategy to rescue C3G. Our findings demonstrate restored inhibition of complement's alternative pathway and long-term reversal of disease without immune rejection using adeno-associated virus (AAV)-mediated delivery of truncated CFH (tCFH) in a Cfh-/- mouse model of C3G. We tested three different tCFH vectors and found significant differences in their relative transduction efficiency and therapeutic efficacy. These discoveries motivate the development of AAV-mediated tCFH replacement therapy for patients with C3G while simultaneously demonstrating proof of concept for AAV-mediated tCFH gene augmentation therapy for patients with AMD.

Moss-derived human complement factor H modulates retinal immune response and attenuates retinal degeneration

BACKGROUND

AMD is a multifactorial progressive disease of the central retina that leads to severe vision loss among the elderly. Genome-wide association studies in AMD patients and preclinical data have identified a dysregulated complement system and aberrant microglia responses in the pathogenesis of AMD. Specifically, a genetic variant in the complement factor H (CFH) gene, an important inhibitor of the alternative complement pathway, confers the strongest risk for AMD. Here, we investigated whether moss-derived recombinant human CFH proteins, termed CPV-101 and CPV-104, can modulate microglia reactivity and limit retinal degeneration in a murine light damage paradigm mimicking important features of AMD.

METHODS

Two glycosylated human recombinant CFH proteins CPV101, and CPV-104 were produced in moss suspension cultures. In addition, glycans of the CPV-104 variant are sialylated, an optimization that makes CPV-104 an analog of human CFH. BALB/cJ mice received intravitreal injections of 5 µg CPV-101 and CPV-104 or vehicle, starting 1 day prior to exposure to 10,000 lx white light for 30 min. The effects of CPV-101 and CPV-104 treatment on mononuclear phagocyte and Müller cell reactivity were analyzed by immunostainings of retinal sections and flat mounts. Gene expression of microglia markers was analyzed using quantitative real-time PCR (qRT-PCR). Optical coherence tomography (OCT); Blue Peak Autofluorescence (BAF); terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and morphometric analyses were used to quantify the extent of retinal degeneration and photoreceptor apoptosis.

RESULTS

Light-exposed mice treated with moss-derived recombinant human full-length CFH showed reduced complement activation and MAC deposition in the retina. Concomitantly, mononuclear phagocyte and Müller cell reactivity in light-exposed retinas were also ameliorated upon CFH substitution. Moreover, attenuated light-induced retinal degeneration was detected in mice that received moss-derived CFH.

CONCLUSION

Modulating the alternative complement pathway using moss-derived recombinant human full-length CFH variant CPV-101 and CPV-104 counter-regulate gliosis and attenuates light-induced retinal degeneration, highlighting a promising concept for the treatment of AMD patients.

Rapidly Progressive Glomerulonephritis

Rapidly progressive glomerulonephritis (RPGN) is a syndrome characterized by a swift decline in kidney function, often over a few months, accompanied by features of nephritic syndrome. It can result in decreased urine output and commonly involves the presence of extensive crescents in kidney biopsies. RPGN is classified into 3 main types based on immune deposit distribution and visualization through immunofluorescence and electron microscopy: antiglomerular basement membrane disease, immune complex glomerulonephritis, and pauci-immune glomerulonephritis. Early diagnosis and prompt treatment are critical to prevent progression to ESRD. Standard treatment options for RPGN include glucocorticoids, cyclophosphamide, or rituximab, with plasma exchange especially important for antiglomerular basement membrane disease and select cases of ANCA-associated vasculitis. Clinical trials for glomerular diseases have primarily excluded patients with RPGN or dialysis dependence. Establishment of clinical registries is required for the optimization of therapeutic protocols for the treatment of RPGN.

The Difficulties of Treating Complement-3-Mediated Glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is a rare disease affecting the complement alternative pathway, categorized into dense deposit disease and C3 glomerulonephritis. Dense deposit disease predominantly affects younger individuals, while C3 glomerulonephritis tends to manifest in older populations. The diseases are characterized by dysregulation of the complement alternative pathway, leading to the deposition of complement components in the glomeruli and subsequent renal dysfunction. Notably, the incidence of C3G in the United States is low, with 1-3 cases per 1,000,000 and a prevalence of 5 cases per 1,000,000.

AREAS OF UNCERTAINTY

Numerous uncertainties persist in comprehending the etiology and pathophysiology of C3G. While biomarkers such as C3 nephritic factor, autoantibodies, and relevant genetic mutations have been identified, their pathogenicity and clinical utility remain unclear. Standard workups involve complement assays and autoantibody panels, yet the definitive diagnostic test remains a kidney biopsy. Nuanced challenges lie in deciphering the sensitivity and specificity of these diagnostic tools, especially in the presence of phenotypical variations among individuals.

THERAPEUTIC ADVANCEMENT

Current therapeutic approaches, albeit lacking robust evidence, encompass a spectrum ranging from supportive care to targeted B-cell therapy and immunosuppression with mycophenolate mofetil and glucocorticoids. For severe and refractory cases, the monoclonal antibody eculizumab, targeting C5 in the complement cascade, is recommended. These treatments, while offering some relief, pose challenges related to their cost and obtaining insurance approval. Exploratory avenues delve into the potential of plasma exchange and innovative treatments such as oral complement inhibitors, reflecting the ongoing quest for effective therapeutic modalities. Trials investigating various complement inhibitors underscore the dynamic landscape of therapeutic advancements in C3G management.

CONCLUSION

In conclusion, the article highlights the complexities of C3G management. The need for further understanding, large-scale trials, and ongoing investigations into disease etiology and pathophysiology is emphasized.

C3 glomerulopathy: a kidney disease mediated by alternative pathway deregulation

C3 glomerulopathy (C3G) is an ultra-rare complement-mediated kidney disease caused by to the deregulation of the alternative pathway (AP) of proximal complement. Consequently, all effector loops of the complement are active and can lead to pathologies, such as C3a- and C5a-mediated inflammation, C3b opsonization, surface C3b-mediated AP C3 convertase assembly, C3 cleavage product deposition in the glomerulus, and lytic C5b-9/MAC cell damage. The most common pathologic mechanisms are defective chronic alternative pathway deregulation, mostly occurring in the plasma, often causing C3 consumption, and chronic complement-mediated glomerular damage. C3G develops over several years, and loss of renal function occurs in more than 50% of patients. C3G is triggered by both genetic and autoimmune alterations. Genetic causes include mutations in individual complement genes and chromosomal variations in the form of deletions and duplications affecting genes encoding complement modulators. Many genetic aberrations result in increased AP C3 convertase activity, either due to decreased activity of regulators, increased activity of modulators, or gain-of-function mutations in genes encoding components of the convertase. Autoimmune forms of C3G do also exist. Autoantibodies target individual complement components and regulators or bind to neoepitopes exposed in the central alternative pathway C3 convertase, thereby increasing enzyme activity. Overactive AP C3 convertase is common in C3G patients. Given that C3G is a complement disease mediated by defective alternative pathway action, complement blockade is an emerging concept for therapy. Here, we summarize both the causes of C3G and the rationale for complement inhibition and list the inhibitors that are being used in the most advanced clinical trials for C3G. With several inhibitors in phase II and III trials, it is expected that effectice treatment for C3G will become availabe in the near future.

An Updated Comprehensive Review on Diseases Associated with Nephrotic Syndromes

There have been exciting advances in our knowledge of primary glomerular diseases and nephrotic syndromes in recent years. Beyond the histological pattern from renal biopsy, more precise phenotyping of the diseases and the use of modern nephrogenetics helps to improve treatment decisions and sometimes also avoid unnecessary exposure to potentially toxic immunosuppression. New biomarkers have led to easier and more accurate diagnoses and more targeted therapeutic decisions. The treatment landscape is becoming wider with a pipeline of promising new therapeutic agents with more sophisticated approaches. This review focuses on all aspects of entities that are associated with nephrotic syndromes with updated information on recent advances in each field. This includes podocytopathies (focal segmental glomerulosclerosis and minimal-change disease), membranous nephropathy, membranoproliferative glomerulonephritis, IgA nephropathy, fibrillary glomerulonephritis, amyloidosis, and monoclonal gammopathy of renal significance in the context of the nephrotic syndrome, but also renal involvement in systemic diseases, diabetic nephropathy, and drugs that are associated with nephrotic syndromes.

Truncated Complement Factor H Y402 Gene Therapy Cures C3 Glomerulonephritis

Patients with both age-related macular degeneration (AMD) and C3 glomerulonephritis (C3G) are challenged by the absence of effective therapies to reverse and eliminate their disease burden. Capitalizing on complement dysregulation as both a significant risk factor for AMD and the known pathophysiology of C3G, we investigated the potential for adeno-associated virus (AAV) delivery of complement factor H (CFH) to rescue C3G in a Cfh-/- mouse model of C3G. While past efforts to treat C3G using exogenous human CFH resulted in limited success before immune rejection led to a foreign protein response, our findings demonstrate the capacity for long-term AAV-mediated delivery of truncated CFH (tCFH) to restore inhibition of the alternative pathway of complement and ultimately reverse C3G without immune rejection. Comparing results from the administration of several tCFH vectors also revealed significant differences in their relative efficiency and efficacy. These discoveries pave the way for subsequent development of AAV-mediated tCFH replacement therapy for patients with C3G, while simultaneously demonstrating proof of concept for a parallel AAV-mediated tCFH gene augmentation therapy for patients with AMD.

The role of complement in kidney disease: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Uncontrolled complement activation can cause or contribute to glomerular injury in multiple kidney diseases. Although complement activation plays a causal role in atypical hemolytic uremic syndrome and C3 glomerulopathy, over the past decade, a rapidly accumulating body of evidence has shown a role for complement activation in multiple other kidney diseases, including diabetic nephropathy and several glomerulonephritides. The number of available complement inhibitor therapies has also increased during the same period. In 2022, Kidney Diseases: Improving Global Outcomes (KDIGO) convened a Controversies Conference, "The Role of Complement in Kidney Disease," to address the expanding role of complement dysregulation in the pathophysiology, diagnosis, and management of various glomerular diseases, diabetic nephropathy, and other forms of hemolytic uremic syndrome. Conference participants reviewed the evidence for complement playing a primary causal or secondary role in progression for several disease states and considered how evidence of complement involvement might inform management. Participating patients with various complement-mediated diseases and caregivers described concerns related to life planning, implications surrounding genetic testing, and the need for inclusive implementation of effective novel therapies into clinical practice. The value of biomarkers in monitoring disease course and the role of the glomerular microenvironment in complement response were examined, and key gaps in knowledge and research priorities were identified.

Update on C3 Glomerulopathy

C3 glomerulopathy (C3G) is a rare disorder marked by deposition of C3 in the glomerulus, resulting in damage to the glomerular filtration unit and presenting with features of the nephritic and nephrotic syndromes. Fundamentally, C3G is caused by dysregulation of the alternative pathway of the complement cascade, either due to genetic variants or acquired humoral factors. Despite significant advances in recent years in the understanding of the underlying mechanisms and culprit lesions that result in the development of C3G, treatment options remain severely limited, and the prognosis is often poor. Fortunately, a number of anticomplement therapies are emerging from the drug development pipeline, with several in late-stage testing in patients with C3G, and there is hope that we will soon have more targeted options for managing patients with this devastating disease. In this review, we provide an overview of C3G, as well as summarizing the evidence for current treatments and detailing the clinical trials that are currently underway.

Recurrent C3 glomerulopathy after kidney transplantation

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

The human factor H protein family - an update

Complement is an ancient and complex network of the immune system and, as such, it plays vital physiological roles, but it is also involved in numerous pathological processes. The proper regulation of the complement system is important to allow its sufficient and targeted activity without deleterious side-effects. Factor H is a major complement regulator, and together with its splice variant factor H-like protein 1 and the five human factor H-related (FHR) proteins, they have been linked to various diseases. The role of factor H in inhibiting complement activation is well studied, but the function of the FHRs is less characterized. Current evidence supports the main role of the FHRs as enhancers of complement activation and opsonization, i.e., counter-balancing the inhibitory effect of factor H. FHRs emerge as soluble pattern recognition molecules and positive regulators of the complement system. In addition, factor H and some of the FHR proteins were shown to modulate the activity of immune cells, a non-canonical function outside the complement cascade. Recent efforts have intensified to study factor H and the FHRs and develop new tools for the distinction, quantification and functional characterization of members of this protein family. Here, we provide an update and overview on the versatile roles of factor H family proteins, what we know about their biological functions in healthy conditions and in diseases.

Complement factor I: Regulatory nexus, driver of immunopathology, and therapeutic

Complement factor I (FI) is the nexus for classical, lectin and alternative pathway complement regulation. FI is an 88 kDa plasma protein that circulates in an inactive configuration until it forms a trimolecular complex with its cofactor and substrate whereupon a structural reorganization allows the catalytic triad to cleave its substrates, C3b and C4b. In keeping with its role as the master complement regulatory enzyme, deficiency has been linked to immunopathology. In the setting of complete FI deficiency, a consumptive C3 deficiency results in recurrent infections with encapsulated microorganisms. Aseptic cerebral inflammation and vasculitic presentations are also less commonly observed. Heterozygous mutations in the factor I gene (CFI) have been demonstrated to be enriched in atypical haemolytic uraemic syndrome, albeit with a very low penetrance. Haploinsufficiency of CFI has also been associated with decreased retinal thickness and is a strong risk factor for the development of age-related macular degeneration. Supplementation of FI using plasma purified or recombinant protein has long been postulated, however, technical difficulties prevented progression into clinical trials. It is only using gene therapy that CFI supplementation has reached the clinic with GT005 in phase I/II clinical trials for geographic atrophy.

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.

Evaluating the clinical utility of measuring levels of factor H and the related proteins

After years of disappointing clinical results, the tide has finally changed and complement targeted-therapies have become a validated and accepted treatment option for several diseases. These accomplishments have revitalized the field and brought renewed attention to the prospects that complement therapeutics can offer. Streamlining diagnostics and therapeutics is imperative in this new era of clinical use of complement therapeutics. However, the incredible success in therapeutics has not been accompanied by the development of novel standardized tools for complement testing. Complement biomarkers can assist in the risk assessment and diagnosis of diseases as well as the prediction of disease progression and treatment response. Recently, a group of complement proteins has been suggested to be highly relevant in various complement-associated disorders, namely the human factor H (FH) protein family. This family of closely related proteins consists of FH, FH-like protein 1, and five factor H-related proteins, and they have been linked to eye, kidney, infectious, vascular, and autoimmune diseases as well as cancer. The goal of this review is to provide a comprehensive overview of the available data on circulating levels of FH and its related proteins in different pathologies. In addition, we examined the current literature to determine the clinical utility of measuring levels of the FH protein family in health and disease. Finally, we discuss future steps that are needed to make their clinical translation a reality.

Association of Histologic Parameters with Outcome in C3 Glomerulopathy and Idiopathic Immunoglobulin-Associated Membranoproliferative Glomerulonephritis

BACKGROUND AND OBJECTIVES

C3 glomerulopathy and idiopathic Ig-associated membranoproliferative GN are kidney diseases characterized by abnormal glomerular complement C3 deposition. These conditions are heterogeneous in outcome, but approximately 50% of patients develop kidney failure within 10 years.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

To improve identification of patients with poor prognosis, we performed a detailed analysis of percutaneous kidney biopsies in a large cohort of patients. Using a validated histologic scoring system, we analyzed 156 native diagnostic kidney biopsies from a retrospective cohort of 123 patients with C3 glomerulopathy and 33 patients with Ig-associated membranoproliferative GN. We used linear regression, survival analysis, and Cox proportional hazards models to assess the relationship between histologic and clinical parameters with outcome.

RESULTS

Frequent biopsy features were mesangial expansion and hypercellularity, glomerular basement membrane double contours, and endocapillary hypercellularity. Multivariable analysis showed negative associations between eGFR and crescents, interstitial inflammation, and interstitial fibrosis/tubular atrophy. Proteinuria positively associated with endocapillary hypercellularity and glomerular basement membrane double contours. Analysis of second native biopsies did not demonstrate associations between immunosuppression treatment and improvement in histology. Using a composite outcome, risk of progression to kidney failure associated with eGFR and proteinuria at the time of biopsy, cellular/fibrocellular crescents, segmental sclerosis, and interstitial fibrosis/tubular atrophy scores.

CONCLUSIONS

Our detailed assessment of kidney biopsy data indicated that cellular/fibrocellular crescents and interstitial fibrosis/tubular atrophy scores were significant determinants of deterioration in kidney function.

A Guide for Adult Nephrologists and Hematologists to Managing Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy in Teens Transitioning to Young Adults

Atypical hemolytic uremic syndrome and C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis are ultra-rare chronic, complement-mediated diseases with childhood manifestation in a majority of cases. Transition of clinical care of patients from pediatric to adult nephrologists-typically with controlled disease in native or transplant kidneys in case of atypical hemolytic uremic syndrome and often with chronic progressive disease despite treatment efforts in case of C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis-identifies a challenging juncture in the journey of these patients. Raising awareness for the vulnerability of this patient cohort; providing education on disease pathophysiology and management including the use of new, high-precision complement antagonists; and establishing an ongoing dialog of patients, families, and all members of the health care team involved on either side of the age divide will be inevitable to ensure optimal patient outcomes and a safe transition of these patients to adulthood.

Use of a B-cell depleting regimen for antifactor H autoantibody-mediated membranoproliferative glomerulonephritis in a paediatric patient

A male child presented initially well with a mixed nephrotic-nephritic syndrome and was commenced on standard high-dose oral corticosteroids. Clinical deterioration occurred 3 weeks later with rapidly progressing renal dysfunction, seizures and diminished urinary output, requiring renal replacement therapy. Once stabilised, renal biopsy demonstrated mesangial and capillary C3, minimal IgG deposition, with mesangial electron dense deposits felt consistent with postinfectious glomerulonephritis or C3 glomerulopathy. Further investigations identified circulating autoantibody directed against factor H, as a plausible aetiology of the membranoproliferative glomerulonephritis (MPGN). Treatment with rituximab and mycophenolate mofetil was associated with a reduction in antibody titres and a concurrent reduction in proteinuria and normalisation of renal function.Subsequent monitoring of antibody titres prompted further administrations of rituximab, with reduction in titres demonstrated after repeat doses. Atypical presentations or complications of nephrotic syndrome or MPGN should prompt detailed investigations for the cause with consideration of antifactor H antibodies.

A clinical approach to children with C3 glomerulopathy

C3 glomerulopathy is a relatively new clinical entity that represents a challenge both to diagnose and to treat. As new therapeutic agents that act as complement inhibitors become available, many with an oral formulation, a better understanding of this disease and of the underlying complement dysregulation driving it has become increasingly useful to optimize patient care. Moreover, recent advances in research have clarified the role of complement in other glomerular diseases in which its role was less established, namely in immune-complex membranoproliferative glomerulonephritis (IC-MPGN), ANCA-vasculitis, IgA nephropathy, and idiopathic membranous nephropathy. Complement inhibitors are being studied in adult and adolescent clinical trials for these indications. This review summarizes current knowledge and future perspectives on every aspect of the diagnosis and management of C3 glomerulopathy and elucidates current understanding of the role of complement in this condition and in other glomerular diseases in children. An overview of ongoing trials involving therapeutic agents targeting complement in glomerular diseases is also provided.

FHR-5 Serum Levels and CFHR5 Genetic Variations in Patients With Immune Complex-Mediated Membranoproliferative Glomerulonephritis and C3-Glomerulopathy

Background

Factor H-related protein 5 (FHR-5) is a member of the complement Factor H protein family. Due to the homology to Factor H, the main complement regulator of the alternative pathway, it may also be implicated in the pathomechanism of kidney diseases where Factor H and alternative pathway dysregulation play a role. Here, we report the first observational study on CFHR5 variations along with serum FHR-5 levels in immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G) patients together with the clinical, genetic, complement, and follow-up data.

Methods

A total of 120 patients with a histologically proven diagnosis of IC-MPGN/C3G were enrolled in the study. FHR-5 serum levels were measured in ELISA, the CFHR5 gene was analyzed by Sanger sequencing, and selected variants were studied as recombinant proteins in ELISA and surface plasmon resonance (SPR).

Results

Eight exonic CFHR5 variations in 14 patients (12.6%) were observed. Serum FHR-5 levels were lower in patients compared to controls. Low serum FHR-5 concentration at presentation associated with better renal survival during the follow-up period; furthermore, it showed clear association with signs of complement overactivation and clinically meaningful clusters.

Conclusions

Our observations raise the possibility that the FHR-5 protein plays a fine-tuning role in the pathogenesis of IC-MPGN/C3G.

Functional Characterization of Rare Genetic Variants in the N-Terminus of Complement Factor H in aHUS, C3G, and AMD

Membranoproliferative glomerulonephritis (MPGN), C3 glomerulopathy (C3G), atypical haemolytic uraemic syndrome (aHUS) and age-related macular degeneration (AMD) have all been strongly linked with dysfunction of the alternative pathway (AP) of complement. A significant proportion of individuals with MPGN, C3G, aHUS and AMD carry rare genetic variants in the CFH gene that cause functional or quantitative deficiencies in the factor H (FH) protein, an important regulator of the AP. In silico analysis of the deleteriousness of rare genetic variants in CFH is not reliable and careful biochemical assessment remains the gold standard. Six N-terminal variants of uncertain significance in CFH were identified in patients with these diseases of the AP and selected for analysis. The variants were produced in Pichia Pastoris in the setting of FH CCPs 1-4, purified by nickel affinity chromatography and size exclusion and characterized by surface plasmon resonance and haemolytic assays as well as by cofactor assays in the fluid phase. A single variant, Q81P demonstrated a profound loss of binding to C3b with consequent loss of cofactor and decay accelerating activity. A further 2 variants, G69E and D130N, demonstrated only subtle defects which could conceivably over time lead to disease progression of more chronic AP diseases such as C3G and AMD. In the variants S159N, A161S, and M162V any functional defect was below the capacity of the experimental assays to reliably detect. This study further underlines the importance of careful biochemical assessment when assigning functional consequences to rare genetic variants that may alter clinical decisions for patients.

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.

C3 glomerulopathy and atypical hemolytic uremic syndrome: an updated review of the literature on alternative complement pathway disorders

The complement system plays a significant role within the pathological process of C3 glomerulopathy (C3GP) and atypical hemolytic uremic syndrome (aHUS). In daily practice, clinicians should differentiate the subgroups of C3GP because of they should apply different treatment modalities. In the past, C3GP was considered as a part of membranoproliferative glomerulonephritis (MPGN). MPGN is defined as glomerular capillary thickening secondary to the synthesis of the new glomerular basement membrane and mesangial cellular hyperplasia with mesangial matrix expansion. Atypical hemolytic uremic syndrome is an ultra-rare disease that can be outlined by the triad of Coombs negative microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Recent advances demonstrated that these diseases share common abnormalities of the control of the alternative complement system. Therefore, nowadays, most researchers advocate that there may be overlap in the pathogenesis of C3GP and aHUS. This review will provide recent novel mechanisms and treatment options in these diseases. For the purposes that we mentioned above and to help clinicians, we aimed to describe the etiology, pathophysiology, and treatment of C3GP and aHUS in this comprehensive review.

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.

Revisiting the role of factor H in age-related macular degeneration: Insights from complement-mediated renal disease and rare genetic variants

Ophthalmologists are long familiar with the eye showing signs of systemic disease, but the association between age-related macular degeneration and abnormal complement activation, common to several renal disorders, has only recently been elucidated. Although complement activation products were identified in drusen almost three decades ago, it was not until the early 21st century that a single-nucleotide polymorphism in the complement factor H gene was identified as a major heritable determinant of age-related macular degeneration, galvanizing global efforts to unravel the pathogenesis of this common disease. Advances in proteomic analyses and familial aggregation studies have revealed distinctive clinical phenotypes segregated by the functional effects of common and rare genetic variants on the mature protein and its splice variant, factor H-like protein 1. The predominance of loss-of-function, N-terminal mutations implicate age-related macular degeneration as a disease of general complement dysregulation, offering several therapeutic avenues for its modulation. Here, we explore the molecular impact of these mutations/polymorphisms on the ability of variant factor H/factor H-like protein 1 to localize to polyanions, pentraxins, proinflammatory triggers, and cell surfaces across ocular and renal tissues and exert its multimodal regulatory functions and their clinical implications. Finally, we critically evaluate key therapeutic and diagnostic efforts in this rapidly evolving field.

Clinical and Pathophysiological Insights Into Immunological Mediated Glomerular Diseases in Childhood

The kidney is often the target of immune system dysregulation in the context of primary or systemic disease. In particular, the glomerulus represents the anatomical entity most frequently involved, generally as the expression of inflammatory cell invasion or circulant or in situ immune-complex deposition. Glomerulonephritis is the most common clinical and pathological manifestation of this involvement. There are no universally accepted classifications for glomerulonephritis. However, recent advances in our understanding of the pathophysiological mechanisms suggest the assessment of immunological features, biomarkers, and genetic analysis. At the same time, more accurate and targeted therapies have been developed. Data on pediatric glomerulonephritis are scarce and often derived from adult studies. In this review, we update the current understanding of the etiologic events and genetic factors involved in the pathogenesis of pediatric immunologically mediated primitive forms of glomerulonephritis, together with the clinical spectrum and prognosis. Possible new therapeutic targets are also briefly discussed.

Clinicopathological Significance and Renal Outcomes of Light Microscopic Patterns in Complement Component 3 Glomerulopathy

BACKGROUND

Complement component 3 glomerulopathy (C3G) is a disease diagnosed based on the predominance of C3 immunostaining in glomeruli. The popular electron microscopic subtyping of C3G into dense deposit disease and C3 glomerulonephritis (GN) is not without limitations. We aimed to study the light microscopic (LM) patterns of C3G along with their clinicopathological correlation and treatment outcome.

METHODS

C3G biopsies were classified into 4 LM patterns (membranoproliferative GN [MPGN], mesangial proliferative GN [MesPGN], diffuse proliferative GN [DPGN], and crescentic GN [CrGN]). These patterns were compared for clinicopathological profile, treatment outcome, and renal survival. Further, predictors of end-stage renal disease (ESRD) were determined using the Cox proportional hazards model.

RESULTS

Of 162 biopsies, there were 83 MPGN, 36 DPGN, 22 MesPGN, and 21 CrGN. Majority of the patients were young, with males being more than females. About half (48%) of the patients received immunosuppression, steroids alone (29%) or steroids with other immunosuppressants (19%). The overall remission rate was 32.7% (median follow-up = 14 months). CKD developed in 46 patients and 31 patients progressed to ESRD. Predictors of progression to ESRD were older age (hazard ratio [HR] = 1.04, p < 0.01), advanced renal failure at presentation (HR = 3.73, p < 0.01), glomerulosclerosis (HR = 5.07, p < 0.01), and severity of interstitial fibrosis and tubular atrophy (HR = 8.25, p = 0.01).

CONCLUSIONS

The LM patterns differed in their clinicopathological profiles, without any significant difference in their renal outcomes. Glomerulosclerosis and interstitial fibrosis portend a poor prognosis. Besides CrGN, MesPGN pattern of C3G presented as a severe form of disease.

Regulation of regulators: Role of the complement factor H-related proteins

The complement system, while being an essential and very efficient effector component of innate immunity, may cause damage to the host and result in various inflammatory, autoimmune and infectious diseases or cancer, when it is improperly activated or regulated. Factor H is a serum glycoprotein and the main regulator of the activity of the alternative complement pathway. Factor H, together with its splice variant factor H-like protein 1 (FHL-1), inhibits complement activation at the level of the central complement component C3 and beyond. In humans, there are also five factor H-related (FHR) proteins, whose function is poorly characterized. While data indicate complement inhibiting activity for some of the FHRs, there is increasing evidence that FHRs have an opposite role compared with factor H and FHL-1, namely, they enhance complement activation directly and also by competing with the regulators FH and FHL-1. This review summarizes the current stand and recent data on the roles of factor H family proteins in health and disease, with focus on the function of FHR proteins.

C4 nephritic factor in patients with immune-complex-mediated membranoproliferative glomerulonephritis and C3-glomerulopathy

BACKGROUND

Acquired or genetic abnormalities of the complement alternative pathway are the primary cause of C3glomerulopathy(C3G) but may occur in immune-complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) as well. Less is known about the presence and role of C4nephritic factor(C4NeF) which may stabilize the classical pathway C3-convertase. Our aim was to examine the presence of C4NeF and its connection with clinical features and with other pathogenic factors.

RESULTS

One hunfe IC-MPGN/C3G patients were enrolled in the study. C4NeF activity was determined by hemolytic assay utilizing sensitized sheep erythrocytes. Seventeen patients were positive for C4NeF with lower prevalence of renal impairment and lower C4d level, and higher C3 nephritic factor (C3NeF) prevalence at time of diagnosis compared to C4NeF negative patients. Patients positive for both C3NeF and C4NeF had the lowest C3 levels and highest terminal pathway activation. End-stage renal disease did not develop in any of the C4NeF positive patients during follow-up period. Positivity to other complement autoantibodies (anti-C1q, anti-C3) was also linked to the presence of nephritic factors. Unsupervised, data-driven cluster analysis identified a group of patients with high prevalence of multiple complement autoantibodies, including C4NeF.

CONCLUSIONS

In conclusion, C4NeF may be a possible cause of complement dysregulation in approximately 10-15% of IC-MPGN/C3G patients.

Complement deficiencies and dysregulation: Pathophysiological consequences, modern analysis, and clinical management

Complement defects are associated with an enhanced risk of a broad spectrum of infectious as well as systemic or local inflammatory and thrombotic disorders. Inherited complement deficiencies have been described for virtually all complement components but can be mimicked by autoantibodies, interfering with the activity of specific complement components, convertases or regulators. While being rare, diseases related to complement deficiencies are often severe with a frequent but not exclusive manifestation during childhood. Whereas defects of early components of the classical pathway significantly increase the risk of autoimmune disorders, lack of components of the terminal pathway as well as of properdin are associated with an enhanced susceptibility to meningococcal infections. The impaired synthesis or function of C1 inhibitor results in the development of hereditary angioedema (HAE). Furthermore, complement dysregulation causes renal disorders such as atypical hemolytic uremic syndrome (aHUS) or C3 glomerulopathy (C3G) but also age-related macular degeneration (AMD). While paroxysmal nocturnal hemoglobinuria (PNH) results from the combined deficiency of the regulatory complement proteins CD55 and CD59, which is caused by somatic mutation of a common membrane anchor, isolated CD55 or CD59 deficiency is associated with the CHAPLE syndrome and polyneuropathy, respectively. Here, we provide an overview on clinical disorders related to complement deficiencies or dysregulation and describe diagnostic strategies required for their comprehensive molecular characterization - a prerequisite for informed decisions on the therapeutic management of these disorders.

Usefulness of mycophenolate mofetil in Indian patients with C3 glomerulopathy

Background

C3 glomerulopathy (C3G) is a heterogeneous disease caused by alternative complement pathway abnormalities without any standardized treatment. An immunosuppressive agent, mycophenolate mofetil (MMF), has been recently shown to be useful in treating C3G, mainly in studies from the west. We report the clinical outcome of 17 Indian C3G patients treated with MMF with or without steroids.

Methods

The clinical and histology details of the C3G patients treated with MMF for at least 6 months with a follow-up of at least 12 months were retrieved from the medical records of our center.

Results

The median serum creatinine and proteinuria at presentation were 0.8 mg/dL and 3.7 g/day, respectively, with the majority (88.2%) presenting as nephrotic syndrome. The mean dose of MMF was 1.65 (±0.56) g/day, and the median duration of MMF therapy was 18 months. Two-thirds (64%) of the patients responded to the treatment, with complete remission in 4 (23%) and partial remission in 7 (41%) (median time: 9 months). Three patients progressed to end-stage renal disease (ESRD) on follow-up. Of the three patients, one (33%) had an initial response in proteinuria to MMF but did not respond after a relapse and subsequently progressed to ESRD and two (67%) other patients were nonresponsive to MMF from the start of the therapy.

Conclusion

Despite a small sample size and lack of a control arm, this study describes the effectiveness of MMF in treating C3G patients from Asia and forms a basis for future randomized trials.

Validation of distinct pathogenic patterns in a cohort of membranoproliferative glomerulonephritis patients by cluster analysis

Background

A novel data-driven cluster analysis identified distinct pathogenic patterns in C3-glomerulopathies and immune complex-mediated membranoproliferative glomerulonephritis. Our aim was to replicate these observations in an independent cohort and elucidate disease pathophysiology with detailed analysis of functional complement markers.

Methods

A total of 92 patients with clinical, histological, complement and genetic data were involved in the study, and hierarchical cluster analysis was done by Ward method, where four clusters were generated.

Results

High levels of sC5b-9 (soluble membrane attack complex), low serum C3 levels and young age at onset (13 years) were characteristic for Cluster 1 with a high prevalence of likely pathogenic variations (LPVs) and C3 nephritic factor, whereas for Cluster 2—which is not reliable because of the small number of cases—strong immunoglobulin G staining, low C3 levels and high prevalence of nephritic syndrome at disease onset were observed. Low plasma sC5b-9 levels, decreased C3 levels and high prevalence of LPV and sclerotic glomeruli were present in Cluster 3, and patients with late onset of the disease (median: 39.5 years) and near-normal C3 levels in Cluster 4. A significant difference was observed in the incidence of end-stage renal disease during follow-up between the different clusters. Patients in Clusters 3–4 had worse renal survival than patients in Clusters 1–2.

Conclusions

Our results confirm the main findings of the original cluster analysis and indicate that the observed, distinct pathogenic patterns are replicated in our cohort. Further investigations are necessary to analyse the distinct biological and pathogenic processes in these patient groups.

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.

A novel mutation in complement 2 accompanied by susceptibility variants in C3 glomerulonephritis: A case study

BACKGROUND

C3 glomerulonephritis is a rare, chronic disease characterized by C3c-dominant staining on renal biopsy and is caused by inherited or acquired alternative complement pathway dysregulation.

CASE PRESENTATION

Here, we reported a 36-year-old man presenting with nephritic syndrome and normal renal function. Secondary causes were excluded by detailed clinical history and laboratory tests. His renal biopsy was consistent with C3 glomerulonephritis with a membranoproliferative glomerulonephritis pattern. To identify the etiology, we carried out genetic and autoantibody screening tests. The results showed he was negative for autoantibodies, while the next-generation sequencing revealed common variants of complement factor H (c.1204T>C; p.Tyr402His), (c.184G>A; p.Val62Ile) and thrombomodulin (c.1418C>T; p.Ala473Val), which have previously been reported to increase susceptibility to complement-mediated diseases. He also carried complement factor H (c.2808G>T; p.Glu936Asp) and mannose-binding lectin (c.161G>A; p.Gly54Asp), putting the patient at an increased risk of infections, which was an important trigger for C3 glomerulonephritis. A novel variant of complement 2 (c.53A>G; p.His18Arg) that might contribute to the occurrence of C3 glomerulonephritis when combined with these susceptibility variants was further identified. The patient was treated with ramipril and regular fresh frozen plasma infusion. He had a good response to treatment with well-controlled proteinuria, stable renal function and an increasing serum C3 level.

CONCLUSIONS

This case adds insight into the pathogenesis of C3 glomerulopathy by showing that a combination of susceptibility variants, genetic mutations and triggers might be responsible for the clinical and pathological phenotypes.

Nephritic Factors: An Overview of Classification, Diagnostic Tools and Clinical Associations

Nephritic factors comprise a heterogeneous group of autoantibodies against neoepitopes generated in the C3 and C5 convertases of the complement system, causing its dysregulation. Classification of these autoantibodies can be clustered according to their stabilization of different convertases either from the classical or alternative pathway. The first nephritic factor described with the capacity to stabilize C3 convertase of the alternative pathway was C3 nephritic factor (C3NeF). Another nephritic factor has been characterized by the ability to stabilize C5 convertase of the alternative pathway (C5NeF). In addition, there are autoantibodies against assembled C3/C5 convertase of the classical and lectin pathways (C4NeF). These autoantibodies have been mainly associated with kidney diseases, like C3 glomerulopathy and immune complex-associated-membranoproliferative glomerulonephritis. Other clinical situations where these autoantibodies have been observed include infections and autoimmune disorders such as systemic lupus erythematosus and acquired partial lipodystrophy. C3 hypocomplementemia is a common finding in all patients with nephritic factors. The methods to measure nephritic factors are not standardized, technically complex, and lack of an appropriate quality control. This review will be focused in the description of the mechanism of action of the three known nephritic factors (C3NeF, C4NeF, and C5NeF), and their association with human diseases. Moreover, we present an overview regarding the diagnostic tools for its detection, and the main therapeutic approach for the patients with nephritic factors.

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.

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.

Diagnostic Utility of Complement Serology for Atypical Hemolytic Uremic Syndrome

OBJECTIVE

To investigate the clinical utility of a 9-analyte complement serology panel (COMS) covering complement function (CH50 and AH50), components (C3, C4), factor B (CFB), factor H, and activation markers (C4d, Bb, and soluble membrane attack complex) for the diagnosis of atypical hemolytic uremic syndrome (aHUS).

METHODS

Physician orders for COMS from January 19, 2015, through November 4, 2016, were reviewed. Demographic characteristics, patient diagnosis, and laboratory parameters were recorded.

RESULTS

There were 177 COMS orders for 147 patients. The median patient age was 44.9 years (range, 0.9-88.0 years). Common reasons for ordering COMS included monitoring and diagnosis of C3 glomerulopathy and renal dysfunction and differentiation of aHUS from other thrombotic microangiopathies (TMAs). Forty-four patients had COMS ordered for TMAs: 8 had aHUS and all had 1 or more abnormalities within the alternative pathway of complement. Although the sensitivity of this finding for the diagnosis of aHUS is 100%, the specificity is only 28%, with a positive likelihood ratio of 1.39. Patients with aHUS had lower CH50, C3, and CFB than did those with secondary non-aHUS TMA (all P<.01). A combined CFB of 20.9 mg/dL or less and CH50 of 56% or less led to sensitivity of 75% with increased specificity of 88.9% and a diagnostic odds ratio of 24.

CONCLUSION

A COMS abnormality should not be interpreted in isolation. In conjunction with clinical presentation, a decrease in both CFB and CH50 may be an important clue to support the diagnosis of aHUS.

Thrombotic microangiopathy after renal transplantation: Current insights in de novo and recurrent disease

Thrombotic microangiopathy (TMA) is one of the most devastating sequalae of kidney transplantation. A number of published articles have covered either de novo or recurrent TMA in an isolated manner. We have, hereby, in this article endeavored to address both types of TMA in a comparative mode. We appreciate that de novo TMA is more common and its prognosis is poorer than recurrent TMA; the latter has a genetic background, with mutations that impact disease behavior and, consequently, allograft and patient survival. Post-transplant TMA can occur as a recurrence of the disease involving the native kidney or as de novo disease with no evidence of previous involvement before transplant. While atypical hemolytic uremic syndrome is a rare disease that results from complement dysregulation with alternative pathway overactivity, de novo TMA is a heterogenous set of various etiologies and constitutes the vast majority of post-transplant TMA cases. Management of both diseases varies from simple maneuvers, e.g., plasmapheresis, drug withdrawal or dose modification, to lifelong complement blockade, which is rather costly. Careful donor selection and proper recipient preparation, including complete genetic screening, would be a pragmatic approach. Novel therapies, e.g., purified products of the deficient genes, though promising in theory, are not yet of proven value.

Common and rare genetic variants of complement components in human disease

Genetic variability in the complement system and its association with disease has been known for more than 50 years, but only during the last decade have we begun to understand how this complement genetic variability contributes to the development of diseases. A number of reports have described important genotype-phenotype correlations that associate particular diseases with genetic variants altering specific aspects of the activation and regulation of the complement system. The detailed functional characterization of some of these genetic variants provided key insights into the pathogenic mechanisms underlying these pathologies, which is facilitating the design of specific anti-complement therapies. Importantly, these analyses have sometimes revealed unknown features of the complement proteins. As a whole, these advances have delineated the functional implications of genetic variability in the complement system, which supports the implementation of a precision medicine approach based on the complement genetic makeup of the patients. Here we provide an overview of rare complement variants and common polymorphisms associated with disease and discuss what we have learned from them.

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.

The MFHR1 Fusion Protein Is a Novel Synthetic Multitarget Complement Inhibitor with Therapeutic Potential

The complement system is essential for host defense, but uncontrolled complement system activation leads to severe, mostly renal pathologies, such as atypical hemolytic uremic syndrome or C3 glomerulopathy. Here, we investigated a novel combinational approach to modulate complement activation by targeting C3 and the terminal pathway simultaneously. The synthetic fusion protein MFHR1 links the regulatory domains of complement factor H (FH) with the C5 convertase/C5b-9 inhibitory fragment of the FH-related protein 1. In vitro, MFHR1 showed cofactor and decay acceleration activity and inhibited C5 convertase activation and C5b-9 assembly, which prevented C3b deposition and reduced C3a/C5a and C5b-9 generation. Furthermore, this fusion protein showed the ability to escape deregulation by FH-related proteins and form multimeric complexes with increased inhibitory activity. In addition to substantially inhibiting alternative and classic pathway activation, MFHR1 blocked hemolysis mediated by serum from a patient with aHUS expressing truncated FH. In FH-/- mice, MFHR1 administration augmented serum C3 levels, reduced abnormal glomerular C3 deposition, and ameliorated C3 glomerulopathy. Taking the unique design of MFHR1 into account, we suggest that the combination of proximal and terminal cascade inhibition together with the ability to form multimeric complexes explain the strong inhibitory capacity of MFHR1, which offers a novel basis for complement therapeutics.

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.

Diseases of complement dysregulation-an overview

Atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and paroxysmal nocturnal hemoglobinuria (PNH) are prototypical disorders of complement dysregulation. Although complement overactivation is common to all, cell surface alternative pathway dysregulation (aHUS), fluid phase alternative pathway dysregulation (C3G), or terminal pathway dysregulation (PNH) predominates resulting in the very different phenotypes seen in these diseases. The mechanism underlying the dysregulation also varies with predominant acquired autoimmune (C3G), somatic mutations (PNH), or inherited germline mutations (aHUS) predisposing to disease. Eculizumab has revolutionized the treatment of PNH and aHUS although has been less successful in C3G. With the next generation of complement therapeutic in late stage development, these archetypal complement diseases will provide the initial targets.

Cluster Analysis Identifies Distinct Pathogenetic Patterns in C3 Glomerulopathies/Immune Complex-Mediated Membranoproliferative GN

Membranoproliferative GN (MPGN) was recently reclassified as alternative pathway complement-mediated C3 glomerulopathy (C3G) and immune complex-mediated membranoproliferative GN (IC-MPGN). However, genetic and acquired alternative pathway abnormalities are also observed in IC-MPGN. Here, we explored the presence of distinct disease entities characterized by specific pathophysiologic mechanisms. We performed unsupervised hierarchical clustering, a data-driven statistical approach, on histologic, genetic, and clinical data and data regarding serum/plasma complement parameters from 173 patients with C3G/IC-MPGN. This approach divided patients into four clusters, indicating the existence of four different pathogenetic patterns. Specifically, this analysis separated patients with fluid-phase complement activation (clusters 1-3) who had low serum C3 levels and a high prevalence of genetic and acquired alternative pathway abnormalities from patients with solid-phase complement activation (cluster 4) who had normal or mildly altered serum C3, late disease onset, and poor renal survival. In patients with fluid-phase complement activation, those in clusters 1 and 2 had massive activation of the alternative pathway, including activation of the terminal pathway, and the highest prevalence of subendothelial deposits, but those in cluster 2 had additional activation of the classic pathway and the highest prevalence of nephrotic syndrome at disease onset. Patients in cluster 3 had prevalent activation of C3 convertase and highly electron-dense intramembranous deposits. In addition, we provide a simple algorithm to assign patients with C3G/IC-MPGN to specific clusters. These distinct clusters may facilitate clarification of disease etiology, improve risk assessment for ESRD, and pave the way for personalized treatment.

Functional Characterization of the Disease-Associated N-Terminal Complement Factor H Mutation W198R

Dysregulation of the complement alternative pathway is involved in the pathogenesis of several diseases, including the kidney diseases atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). In a patient, initially diagnosed with chronic glomerulonephritis, possibly C3G, and who 6 years later had an episode of aHUS, a heterozygous missense mutation leading to a tryptophan to arginine exchange (W198R) in the factor H (FH) complement control protein (CCP) 3 domain has previously been identified. The aim of this study was to clarify the functional relevance of this mutation. To this end, wild-type (FH1-4_WT) and mutant (FH1-4_W198R) CCPs 1-4 of FH were expressed as recombinant proteins. The FH1-4_W198R mutant showed decreased C3b binding compared with FH1-4_WT. FH1-4_W198R had reduced cofactor and decay accelerating activity compared with the wild-type protein. Hemolysis assays demonstrated impaired capacity of FH1-4_W198R to protect rabbit erythrocytes from human complement-mediated lysis, and also to prevent lysis of sheep erythrocytes in human serum induced by a monoclonal antibody binding in FH CCP5 domain, compared with that of FH1-4_WT. Thus, the FH W198R exchange results in impaired complement alternative pathway regulation. The heterozygous nature of this mutation in the index patient may explain the manifestation of two diseases, likely due to different triggers leading to complement dysregulation in plasma or on cell surfaces.

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.

C3 glomerulopathy

C3 glomerulopathy is a recently defined entity that encompasses a group of kidney diseases caused by abnormal control of complement activation with deposition of complement component C3 in glomeruli leading to variable glomerular inflammation. Before the recognition of the unique pathogenesis of these cases, they were variably classified according to their morphological features. C3 glomerulopathy accounts for roughly 1% of all renal biopsies. Clear definition of this entity has allowed a better understanding of its pathogenesis and clinical course and is likely to lead to the design of rational therapies over the next few years.