C3 glomerulonephritis secondary to mutations in factors H and I: rapid recurrence in deceased donor kidney transplant effectively treated with eculizumab

Childhood onset C3 glomerulopathy: recurrence after kidney transplantation-a case series

Background

C3 Glomerulopathy (C3G) is a complement-mediated disease, with predominant C3 deposits, where pathogenic genetic variants in complement system components and circulating autoantibodies result in loss of control of the alternative pathway, have been described. A high incidence of disease recurrence including graft failure has been reported after kidney transplantation (KTx). Currently treatment modalities for preventing and treating post KTx C3G recurrence (plasma exchange, rituximab and eculizumab) in adults have yielded inconsistent results. Data on post KTx C3G recurrence in childhood-onset C3G is still unknown.

Methods

A comprehensive case study of patients diagnosed with C3G as children or adolescents, who underwent KTx between the years 2015-2023. Data collected included complement workup, treatment modalities, and outcomes.

Results

19 patients with C3G were identified during the study period. Five patients developed ESRD and received a kidney transplant. C3G recurrence was diagnosed post KTx in 100% of patients. Graft function improved in 3 of these patients (two with anti-factor H antibodies) after eculizumab treatment, one patient reached graft failure 9 months after transplantation despite eculizumab, recieved a second successful transplantation with pre-emptive eculizumab treatment and one patient showed histologic signs of disease recurrence without clinical signs.

Conclusions

C3G recurrence after KTx in patients diagnosed as children or adolescents may be higher than previously described. Treatment with eculizumab is beneficial in some patients. New treatments are needed for improving post-transplant outcome in patients with C3G.

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 Complement System in Kidney Transplantation

Kidney transplantation is the therapy of choice for patients who suffer from end-stage renal diseases. Despite improvements in surgical techniques and immunosuppressive treatments, long-term graft survival remains a challenge. A large body of evidence documented that the complement cascade, a part of the innate immune system, plays a crucial role in the deleterious inflammatory reactions that occur during the transplantation process, such as brain or cardiac death of the donor and ischaemia/reperfusion injury. In addition, the complement system also modulates the responses of T cells and B cells to alloantigens, thus playing a crucial role in cellular as well as humoral responses to the allograft, which lead to damage to the transplanted kidney. Since several drugs that are capable of inhibiting complement activation at various stages of the complement cascade are emerging and being developed, we will discuss how these novel therapies could have potential applications in ameliorating outcomes in kidney transplantations by preventing the deleterious effects of ischaemia/reperfusion injury, modulating the adaptive immune response, and treating antibody-mediated rejection.

Alternative pathway diagnostics

Uncontrolled alternative pathway activation is the primary driver of several diseases, and it contributes to the pathogenesis of many others. Consequently, diagnostic tests to monitor this arm of the complement system are increasingly important. Defects in alternative pathway regulation are strong risk factors for disease, and drugs that specifically block the alternative pathway are entering clinical use. A range of diagnostic tests have been developed to evaluate and monitor the alternative pathway, including assays to measure its function, expression of alternative pathway constituents, and activation fragments. Genetic studies have also revealed many disease-associated variants in alternative pathway genes that predict the risk of disease and prognosis. Newer imaging modalities offer the promise of non-invasively detecting and localizing pathologic complement activation. Together, these various tests help in the diagnosis of disease, provide important prognostic information, and can help guide therapy with complement inhibitory drugs.

The yin and the yang of early classical pathway complement disorders

The classical pathway of the complement cascade has been recognized as a key activation arm, partnering with the lectin activation arm and the alternative pathway to cleave C3 and initiate the assembly of the terminal components. While deficiencies of classical pathway components have been recognized since 1966, only recently have gain-of-function variants been described for some of these proteins. Loss-of-function variants in C1, C4, and C2 are most often associated with lupus and systemic infections with encapsulated bacteria. C3 deficiency varies slightly from this phenotypic class with membranoproliferative glomerulonephritis and infection as the dominant phenotypes. The gain-of-function variants recently described for C1r and C1s lead to periodontal Ehlers Danlos syndrome, a surprisingly structural phenotype. Gain-of-function in C3 and C2 are associated with endothelial manifestations including hemolytic uremic syndrome and vasculitis with C2 gain-of-function variants thus far having been reported in patients with a C3 glomerulopathy. This review will discuss the loss-of-function and gain-of-function phenotypes and place them within the larger context of complement deficiencies.

Complement Factor I Variants in Complement-Mediated Renal Diseases

C3 glomerulopathy (C3G) and atypical hemolytic uremic syndrome (aHUS) are two rare diseases caused by dysregulated activity of the alternative pathway of complement secondary to the presence of genetic and/or acquired factors. Complement factor I (FI) is a serine protease that downregulates complement activity in the fluid phase and/or on cell surfaces in conjunction with one of its cofactors, factor H (FH), complement receptor 1 (CR1/CD35), C4 binding protein (C4BP) or membrane cofactor protein (MCP/CD46). Because altered FI activity is causally related to the pathogenesis of C3G and aHUS, we sought to test functional activity of select CFI missense variants in these two patient cohorts. We identified 65 patients (16, C3G; 48, aHUS; 1 with both) with at least one rare variant in CFI (defined as a MAF < 0.1%). Eight C3G and eleven aHUS patients also carried rare variants in either another complement gene, ADAMTS13 or THBD. We performed comprehensive complement analyses including biomarker profiling, pathway activity and autoantibody testing, and developed a novel FI functional assay, which we completed on 40 patients. Seventy-eight percent of rare CFI variants (31/40) were associated with FI protein levels below the 25th percentile; in 22 cases, FI levels were below the lower limit of normal (type 1 variants). Of the remaining nine variants, which associated with normal FI levels, two variants reduced FI activity (type 2 variants). No patients carried currently known autoantibodies (including FH autoantibodies and nephritic factors). We noted that while rare variants in CFI predispose to complement-mediated diseases, phenotypes are strongly contingent on the associated genetic background. As a general rule, in isolation, a rare CFI variant most frequently leads to aHUS, with the co-inheritance of a CD46 loss-of-function variant driving the onset of aHUS to the younger age group. In comparison, co-inheritance of a gain-of-function variant in C3 alters the phenotype to C3G. Defects in CFH (variants or fusion genes) are seen with both C3G and aHUS. This variability underscores the complexity and multifactorial nature of these two complement-mediated renal diseases.

Role of Complement System in Kidney Transplantation: Stepping From Animal Models to Clinical Application

Kidney transplantation is a life-saving strategy for patients with end-stage renal diseases. Despite the advances in surgical techniques and immunosuppressive agents, the long-term graft survival remains a challenge. Growing evidence has shown that the complement system, part of the innate immune response, is involved in kidney transplantation. Novel insights highlighted the role of the locally produced and intracellular complement components in the development of inflammation and the alloreactive response in the kidney allograft. In the current review, we provide the updated understanding of the complement system in kidney transplantation. We will discuss the involvement of the different complement components in kidney ischemia-reperfusion injury, delayed graft function, allograft rejection, and chronic allograft injury. We will also introduce the existing and upcoming attempts to improve allograft outcomes in animal models and in the clinical setting by targeting the complement system.

Homodimeric Minimal Factor H: In Vivo Tracking and Extended Dosing Studies in Factor H Deficient Mice

C3 glomerulopathy (C3G) is associated with dysregulation of the alternative pathway (AP) of complement and treatment options remain inadequate. Factor H (FH) is a potent regulator of the AP. An in-depth analysis of FH-related protein dimerised minimal (mini)-FH constructs has recently been published. This analysis showed that addition of a dimerisation module to mini-FH not only increased serum half-life but also improved complement regulatory function, thus providing a potential treatment option for C3G. Herein, we describe the production of a murine version of homodimeric mini-FH [mHDM-FH (mFH1-5^18-20^R1-2)], developed to reduce the risk of anti-drug antibody formation during long-term experiments in murine models of C3G and other complement-driven pathologies. Our analysis of mHDM-FH indicates that it binds with higher affinity and avidity to WT mC3b when compared to mouse (m)FH (mHDM-FH KD=505 nM; mFH KD=1370 nM) analogous to what we observed with the respective human proteins. The improved binding avidity resulted in enhanced complement regulatory function in haemolytic assays. Extended interval dosing studies in CFH-/- mice (5mg/kg every 72hrs) were partially effective and bio-distribution analysis in CFH-/- mice, through in vivo imaging technologies, demonstrates that mHDM-FH is preferentially deposited and remains fixed in the kidneys (and liver) for up to 4 days. Extended dosing using an AAV- human HDM-FH (hHDM-FH) construct achieved complete normalisation of C3 levels in CFH-/- mice for 3 months and was associated with a significant reduction in glomerular C3 staining. Our data demonstrate the ability of gene therapy delivery of mini-FH constructs to enhance complement regulation in vivo and support the application of this approach as a novel treatment strategy in diseases such as C3G.

Beyond Panel-Based Testing: Exome Analysis Increases Sensitivity for Diagnosis of Genetic Kidney Disease

BACKGROUND

Next-generation sequencing (NGS) is a useful tool for evaluating patients with suspected genetic kidney disease. Clinical practice relies on the use of targeted gene panels that are ordered based on patient presentation. We compare the diagnostic yield of clinical panel-based testing to exome analysis.

METHODS

In total, 324 consecutive patients underwent physician-ordered, panel-based NGS testing between December 2014 and October 2018. Gene panels were available for four clinical phenotypes, including atypical hemolytic uremic syndrome (n=224), nephrotic syndrome (n=56), cystic kidney disease (n=26), and Alport syndrome (n=13). Variants were analyzed and clinical reports were signed out by a pathologist or clinical geneticist at the time of testing. Subsequently, all patients underwent retrospective exome analysis to detect additional clinically significant variants in kidney disease genes that were not analyzed as part of the initial clinical gene panel. Resulting variants were classified according to the American College of Medical Genetics and Genomics 2015 guidelines.

RESULTS

In the initial physician-ordered gene panels, we identified clinically significant pathogenic or likely pathogenic variants in 13% of patients (n=42/324). CFHR3-CFHR1 homozygous deletion was detected in an additional 13 patients with aHUS without a pathogenic or likely pathogenic variant. Diagnostic yield of the initial physician-ordered gene panel was 20% and varied between groups. Retrospective exome analysis identified 18 patients with a previously unknown pathogenic or likely pathogenic variant in a kidney disease gene and eight patients with a high-risk APOL1 genotype. Overall, retrospective exome analysis increased the diagnostic yield of panel-based testing from 20% to 30%.

CONCLUSIONS

These results highlight the importance of a broad and collaborative approach between the clinical laboratory and their physician clients that employs additional analysis when a targeted panel of kidney disease-causing genes does not return a clinically meaningful result.

Diverse Clinical Presentations of C3 Dominant Glomerulonephritis

C3 dominant immunofluorescence staining is present in a subset of patients with idiopathic immune complex membranoproliferative glomerulonephritis (iMPGN). It is increasingly recognized that iMPGN may be complement driven, as are cases of "typical" C3 glomerulopathy (C3G). In both iMPGN and C3G, a frequent membranoproliferative pattern of glomerular injury may indicate common pathogenic mechanisms via complement activation and endothelial cell damage. Dysregulation of the alternative complement pathway and mutations in certain regulatory factors are highly implicated in C3 glomerulopathy (which encompasses C3 glomerulonephritis, dense deposit disease, and cases of C3 dominant MPGN). We report three cases that demonstrate that an initial biopsy diagnosis of iMPGN does not exclude complement alterations similar to the ones observed in patients with a diagnosis of C3G. The first patient is a 39-year-old woman with iMPGN and C3 dominant staining, with persistently low C3 levels throughout her course. The second case is a 22-year-old woman with elevated anti-factor H antibodies and C3 dominant iMPGN findings on biopsy. The third case is a 25-year-old woman with C3 dominant iMPGN, dense deposit disease, and a crescentic glomerulonephritis on biopsy. We present the varied phenotypic variations of C3 dominant MPGN and review clinical course, complement profiles, genetic testing, treatment course, and peri-transplantation plans. Testing for complement involvement in iMPGN is important given emerging treatment options and transplant planning.

Complementopathies and precision medicine

The renaissance of complement diagnostics and therapeutics has introduced precision medicine into a widened field of complement-mediated diseases. In particular, complement-mediated diseases (or complementopathies) with ongoing or published clinical trials of complement inhibitors include paroxysmal nocturnal hemoglobinuria, cold agglutinin disease, hemolytic uremic syndrome, nephropathies, HELLP syndrome, transplant-associated thrombotic microangiopathy, antiphospholipid antibody syndrome, myasthenia gravis, and neuromyelitis optica. Recognizing that this field is rapidly expanding, we aim to provide a state-of-the-art review of (a) current understanding of complement biology for the clinician, (b) novel insights into complement with potential applicability to clinical practice, (c) complement in disease across various disciplines (hematology, nephrology, obstetrics, transplantation, rheumatology, and neurology), and (d) the potential future of precision medicine. Better understanding of complement diagnostics and therapeutics will not only facilitate physicians treating patients in clinical practice but also provide the basis for future research toward precision medicine in this field.

Poor allograft outcome in Indian patients with post-transplant C3 glomerulopathy

Background

Complement 3 glomerulopathy (C3G) results from dysfunction of the alternative complement pathway (ACP). No data are available on post-transplant C3G in South Asia.

Methods

In this study, renal allograft biopsies of C3G patients performed from 2012 to 2017 were analysed for ACP functional assay (APFA), serum complement levels, complement factor H (CFH), complement factor B (CFB) and autoantibodies to CFH and CFB. Limited genetic screening for CFH/CFHR5 genes was carried out. All study patients were also followed up.

Results

A total of 21 cases of C3G were included, of which 11 had native C3G disease (that is, recurrent C3G). Of these 11 recurrent cases, 7 presented with allograft dysfunction and 4 with proteinuria and renal dysfunction. Early post-transplant recurrence (<1 month) was noted in six patients, whereas recurrence in five patients occurred within 8–17 months of transplant. Biopsies showed mild focal mesangial expansion with or without endocapillary proliferation and thrombotic microangiopathy. Rejection was also noted in six patients. APFA/C3 levels were low in all cases. Serum CFH levels were low [dense deposit disease (DDD), 44%; C3 glomerulonephritis (C3GN), 25%], whereas CFB levels were normal. Autoantibodies to CFH, CFB and C3 nephritic factor were present in 11, 0 and 44% of DDD cases, respectively, and in 17, 17 and 33% of C3GN cases, respectively. Genetic analysis revealed only non-pathogenic CFH gene variants (93%). No novel mutation was found. At follow-up (140 months), stable graft was noted in 28% of cases, progressive renal failure in 19%, graft loss in 34%, and 19% of patients died.

Conclusion

Post-transplant C3G can present with graft dysfunction and/or proteinuria. Subtle histological findings demand careful interpretation of immunofluorescence results. Autoantibodies to complement pathway regulatory proteins are common, and no novel mutation has been found from limited genetic workup. Clinical outcome is poor.

Invasive meningococcal disease in patients with complement deficiencies: a case series (2008-2017)

BACKGROUND

To describe patients with inherited and acquired complement deficiency who developed invasive meningococcal disease (IMD) in England over the last decade.

METHODS

Public Health England conducts enhanced surveillance of IMD in England. We retrospectively identified patients with complement deficiency who developed IMD in England during 2008-2017 and retrieved information on their clinical presentation, vaccination status, medication history, recurrence of infection and outcomes, as well as characteristics of the infecting meningococcal strain.

RESULTS

A total of 16 patients with 20 IMD episodes were identified, including four with two episodes. Six patients had inherited complement deficiencies, two had immune-mediated conditions associated with complement deficiency (glomerulonephritis and vasculitis), and eight others were on Eculizumab therapy, five for paroxysmal nocturnal haemoglobinuria and three for atypical haemolytic uraemic syndrome. Cultures were available for 7 of 11 episodes among those with inherited complement deficiencies/immune-mediated conditions and the predominant capsular group was Y (7/11), followed by B (3/11) and non-groupable (1/11) strains. Among patients receiving Eculizumab therapy, 3 of the 9 episodes were due to group B (3/9), three others were NG but genotypically group B, and one case each of groups E, W and Y.

CONCLUSIONS

In England, complement deficiency is rare among IMD cases and includes inherited disorders of the late complement pathway, immune-mediated disorders associated with low complement levels and patients on Eculizumab therapy. IMD due to capsular group Y predominates in patient with inherited complement deficiency, whilst those on Eculizumab therapy develop IMD due to more diverse capsular groups including non-encapsulated strains.

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.