Patterns of Clinical Response to Eculizumab in Patients With C3 Glomerulopathy.

BACKGROUND: Cases reports and small series of patients with C3 glomerulopathy have reported variable efficacy of eculizumab. STUDY DESIGN: Case series of C3 glomerulopathy. SETTING & PARTICIPANTS: Pediatric and adult patients with C3 glomerulopathy treated with eculizumab between 2010 and 2016 were identified through the C3 glomerulopathy French registry database, and a questionnaire was sent to participating French pediatric and adult nephrology centers, as well as one pediatric referral center in Québec, Canada. OUTCOMES: Global or partial clinical renal response. MEASUREMENTS: Evolution of serum creatinine and proteinuria values. RESULTS: 26 patients (13 children/adolescents) were included. 22 (85%) patients had received steroids, plasma exchange, or immunosuppressive therapy before eculizumab, and 3 of them had rapid progression of their kidney disease despite treatment. At the initiation of eculizumab therapy, 11 (42%) patients had chronic kidney disease, 7 (27%) had rapidly progressive disease, and 3 (12%) required dialysis. After eculizumab treatment (median duration, 14 months), 6 (23%) patients had a global clinical response; 6 (23%), a partial clinical response; and 14 (54%), no response. Compared with those who had a partial clinical or no response, patients who had a global clinical response had lower estimated glomerular filtration rates, a more rapidly progressive course, and more extracapillary proliferation on kidney biopsy. Age, extent of renal fibrosis, frequency of nephrotic syndrome, low serum C3 and C3 nephritic factor and elevated soluble C5b-9 concentrations, or complement gene variants did not differ between responders and nonresponders. LIMITATIONS: Retrospective design without a control group, relatively small number of cases, inclusion of pediatric and adult cases. CONCLUSIONS: Eculizumab appears to be a potential treatment for patients with crescentic rapidly progressive C3 glomerulopathy. Its benefit in patients with non-rapidly progressing forms seems to be limited.

Modeling C3 glomerulopathies: C3 convertase regulation on an extracellular matrix surface.

Introduction: C3 glomerulopathies (C3G) are ultra-rare complement-mediated diseases that lead to end-stage renal disease (ESRD) within 10 years of diagnosis in ~50% of patients. Overactivation of the alternative pathway (AP) of complement in the fluid phase and on the surface of the glomerular endothelial glycomatrix is the underlying cause of C3G. Although there are animal models for C3G that focus on genetic drivers of disease, in vivo studies of the impact of acquired drivers are not yet possible. Methods: Here we present an in vitro model of AP activation and regulation on a glycomatrix surface. We use an extracellular matrix substitute (MaxGel) as a base upon which we reconstitute AP C3 convertase. We validated this method using properdin and Factor H (FH) and then assessed the effects of genetic and acquired drivers of C3G on C3 convertase. Results: We show that C3 convertase readily forms on MaxGel and that this formation was positively regulated by properdin and negatively regulated by FH. Additionally, Factor B (FB) and FH mutants impaired complement regulation when compared to wild type counterparts. We also show the effects of C3 nephritic factors (C3Nefs) on convertase stability over time and provide evidence for a novel mechanism of C3Nef-mediated C3G pathogenesis. Discussion: We conclude that this ECM-based model of C3G offers a replicable method by which to evaluate the variable activity of the complement system in C3G, thereby offering an improved understanding of the different factors driving this disease process.

Detection of C3 Nephritic Factor by Hemolytic Assay.

C3 nephritic Factor (C3NeF) is autoantibody that binds neoepitopes of the C3 convertase C3bBb, resulting in a stabilization of the enzyme. First functional characterizations of C3NeF were performed by hemolytic assays using preactivated sheep erythrocytes (bearing C3b). Sheep erythrocytes are beforehand sensitized with an anti-sheep red blood cell stroma antibody produced in rabbit (hemolysin). Sensitized sheep erythrocytes will initiate cascade complement activation via the classic pathway, followed by alternative pathway amplification loop, resulting in C3b covalent binding to cell surface. Sheep erythrocytes bearing C3b permit the alternative pathway exploration, in particular decay of alternative pathway C3 convertase.

Outcome of C3 glomerulopathy patients: largest single-centre experience from South Asia.

BACKGROUND: C3 glomerulopathy (C3G) is related to dysfunction of alternative complement pathway (ACP) because of its hyperactivation. Triggering factors and genetic profile are likely to be different in developing countries as compared to the Western world. Data regarding C3G from South Asian is scanty. STUDY DESIGN: In the present study, 115 patients of C3G from 2012 to 2017 were analyzed. Clinical details were reviewed; serological levels of C3, C4, complement factor H or B and autoantibody testing was done by nephelometry/ELISA. Limited genetics workup for CFH and CFHR5 genes was done. RESULTS: The prevalence of C3G was 1.52%. There was no difference in demographic and histopathologic profiles of C3G patients. Majority of patients had low functional assay and C3 levels. C3 nephritic factor was present in 47.5% of DDD and 38.6% of C3GN. Autoantibodies to CFH were present more often in the patients of C3GN (29.5%) than DDD (12.5%). Autoantibodies to CFB were equally common in both groups. Past history of infections was present in one-third patients and monoclonal paraproteins were present only in two patients. No pathogenic variants were noted in CFH/CFHR5 gene. On follow-up (3.2 + 1.6 years), complete and partial remission was achieved in one-fourth patients and 26% had resistance disease. About 40% progressed to ESRD and 18 underwent renal transplantation of which nine had a post-transplant recurrence. CONCLUSIONS: Indian cohort had some differences in the immunological and genetic profile when compared to the Western literature; most significant was the absence of monoclonal immunoglobulins as a trigger for C3G.

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.

Gain of function mutant of complement factor B K323E mimics pathogenic C3NeF autoantibodies in convertase assays.

Complement convertases are enzymatic complexes, which play a critical role in propagation and amplification of the complement cascade. Under physiological conditions, convertases decay shortly after being formed in either spontaneous or inhibitor-driven process. Prolongation of their half-life by C3NeF autoantibodies that prevent convertase dissociation results in pathogenic condition often manifested by renal diseases. However, the diagnosis of convertase abnormalities is difficult due to the labile nature of these enzymes and low credibility of existing methods. Only recently, two-step functional assays employing C5-depleted serum or C5 inhibitors were introduced. Their advantage is convertase formation in the physiological milieu of whole serum and the drawback is inter-assay variability due to variations in rabbit erythrocytes used for the haemolysis-based readout. Abovementioned problems demand the application of the internal standard in each experiment. Obtaining a defined preparation of autoantibodies is complicated due to ethical and practical considerations. We found that recombinant, his-tagged factor B (fB) variant K323E retains full hemolytic activity and possess the ability to form convertases with prolonged half-life either in fB-depleted serum or when mixed with normal human serum. Such dominant character of K323E mutation allows using recombinant protein as a reference in functional convertase assays, not limited to these using rabbit erythrocytes. Additionally, our results demonstrate that gain of function mutations in complement components mimic the phenotype of C3NeF. Hence, patients with such "genetic C3NeF" would not benefit from B-cell depletion (e.g. by rituximab) and therefore should be properly diagnosed in order to choose suitable therapeutic intervention.

Acquired partial lipodystrophy and C3 glomerulopathy: Dysregulation of the complement system as a common pathogenic mechanism. / Lipodistrofia parcial adquirida y glomerulopatía C3: la desregulación del sistema del complemento como mecanismo común.

The activation of the alternative pathway of the complement is involved in the development of several renal diseases, such as atypical haemolytic uremic syndrome and C3 glomerulopathy. In C3 glomerulopathy, a high percentage of patients have circulating levels of the autoantibody called C3NeF, which causes systemic dysregulation of the complement system. In some cases, the presence of this antibody has been related with abnormalities of adipose tissue, causing acquired partial lipodystrophy (Barraquer-Simons syndrome). Acquired partial lipodystrophy is an extremely rare disorder affecting the distribution of subcutaneous adipose tissue and that mainly onsets during childhood. These patients, in addition to possibly presenting with all the metabolic disorders associated with the adipose tissue defect, present with C3 hypocomplementemia and C3NeF and 25% have developed C3 glomerulopathy. Although it has been known for some time how the dysregulation of the complement system affects the kidneys, it remains unknown how it exactly affects adipose tissue; nevertheless, the relationship is quite clear. In this paper, we describe the connection between the complement system with the biology of the adipose tissue and its pathogenesis reflected from acquired partial lipodystrophy.

Autoantibodies against alternative complement pathway proteins in renal pathologies. / Autoanticuerpos frente a proteínas de la vía alternativa del complemento en enfermedad renal.

Complement system activation plays an important role in several renal pathologies, including antibody-mediated glomerulonephritis, ischaemia-reperfusion injury of trasplanted kidneys or renal allograft rejection. Besides these conditions, alternative pathway abnormalities are directly involved in the pathogenesis of C3 glomerulopathies and atypical haemolytic uraemic syndrome. These abnormalities may be inherited or acquired, the latter as autoantibodies directed against the various components and regulators of the alternative complement pathway. The functional consequences of some of these antibodies and their association with these conditions are well known, whereas for other antibodies only isolated cases have been reported. This article describes the autoantibodies that target the alternative complement pathway proteins, their characteristics and their clinical relevance in renal pathologies.