Complement therapy in atypical haemolytic uraemic syndrome (aHUS)

Contribution of animal models to the mechanistic understanding of Alternative Pathway and Amplification Loop (AP/AL)-driven Complement-mediated Diseases

This review aimed to capture the key findings that animal models have provided around the role of the alternative pathway and amplification loop (AP/AL) in disease. Animal models, particularly mouse models, have been incredibly useful to define the role of complement and the alternative pathway in health and disease; for instance, the use of cobra venom factor and depletion of C3 provided the initial insight that complement was essential to generate an appropriate adaptive immune response. The development of knockout mice have further underlined the importance of the AP/AL in disease, with the FH knockout mouse paving the way for the first anti-complement drugs. The impact from the development of FB, properdin, and C3 knockout mice closely follows this in terms of mechanistic understanding in disease. Indeed, our current understanding that complement plays a role in most conditions at one level or another is rooted in many of these in vivo studies. That C3, in particular, has roles beyond the obvious in innate and adaptive immunity, normal physiology, and cellular functions, with or without other recognized AP components, we would argue, only extends the reach of this arm of the complement system. Humanized mouse models also continue to play their part. Here, we argue that the animal models developed over the last few decades have truly helped define the role of the AP/AL in disease.

Case report: Novel FHR2 variants in atypical Hemolytic Uremic Syndrome: A case study of a translational medicine approach in renal transplantation

Atypical hemolytic–uremic syndrome (aHUS) is a severe thrombotic microangiopathy in which kidney involvement is common. aHUS can be due to either genetic or acquired abnormalities, with most abnormalities affecting the alternative complement pathway. Several genetic factors/alterations can drive the clinical presentation, therapeutic response, and risk of recurrence, especially recurrence following kidney transplantation. We report here the case of a 22-year-old man who developed a severe form of aHUS. Renal biopsy revealed thrombotic microangiopathy and features of chronic renal damage. Despite two eculizumab infusions, the patient remained dialysis dependent. Two novel rare variants, c.109G>A (p.E37K) and c.159 C>A (p.Y53*), were identified in the factor H-related 2 (FHR2) gene, and western blot analysis revealed a significant reduction in the level of FHR2 protein in the patient’s serum. Although FHR2 involvement in complement 3 glomerulopathy has been reported previously, a role for FRH2 as a complement modulator has not yet been definitively shown. In addition, no cases of aHUS in individuals with FHR2 variants have been reported. Given the role of FHRs in the complement system and the fact that this patient was a candidate for a kidney transplant, we studied the relevance of low FHR2 plasma levels through a set of functional in vitro assays. The aim of our work was to determine if low FHR2 plasma levels could influence complement control at the endothelial surface with a view to identifying a therapeutic approach tailored to this specific patient. Interestingly, we observed that low FHR2 levels in the patient’s serum could induce complement activation, as well as C5b–9 deposition on human endothelial cells, and affected cell morphology. As C5b–9 deposition is a prerequisite for endothelial cell damage, these results suggest that extremely low FHR2 plasma levels increase the risk of aHUS. Given their ability to reduce C5b–9 deposition, recombinant FHR2 and eculizumab were tested in vitro and found to inhibit hemolysis and endothelial cell surface damage. Both molecules showed effective and comparable profiles. Based on these results, the patient underwent a kidney transplant, and received eculizumab as induction and maintenance therapy. Five years after transplantation, the patient remains in good general health, with stable graft function and no evidence of disease recurrence. To our knowledge, this is first reported case of an aHUS patient carrying FHR2 mutations and provides an example of a translational therapeutic approach in kidney transplantation.

Association of Palm gene mutations with structure and function of paralemmin proteins in Lori-Bakhtiari and Zel sheep Breeds

The aim of current study was to survey genetic variability of PALM gene’s exon 3 and 4 by PCR-SSCP and DNA sequencing in Zel and Lori Bakhtiari sheep breeds. The SIFT (Sorting Intolerant from Tolerant) and PHyre2 program were used to predict the possible impact of amino acid substitutions on performance and structure of the paralemmin protein. A total of 140 animal's from 2 Iranian sheep breeds with different fat metabolisms, Lori-Bakhtiari and Zel sheep breeds were considered. The results showed that there are two polymorphic sites including a nonsynonymous substitution and an insertion mutation (49bp). Non-synonymous mutation deduced Thr20Ala amino acid exchange and ensuing two different structures for paralemmin protein that could be potentially affect protein structure and function during the interaction with glutamate in the cytosolic surface of plasma membrane. PALM gene, according to evolutionary path, is classified into two separate categories. In first covey, Gallus gallus and in second one, other species in several branches, so that the sequence of cow and sheep is placed in a sub-branch which forms a clade beside goat. Comparison of illustrated coding region sequences, PALM gene among different species, is of orthologous which are derived from a common ancestor.

Genetic abnormalities in biopsy-proven, adult-onset hemolytic uremic syndrome and C3 glomerulopathy

Abstract

Atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) have been linked to mutations in many of the proteins that are involved in alternative complement pathway activation. Age and etiology confounded, the prevalence of such mutations has been reported to be over 30 to 50% in these diseases. However, the cohorts studied included many children or individuals with a familial history of complement-related disorders and genetic tests were usually limited to exome sequencing of known causative or risk-associated genes. In this study, a retrospective adult cohort of 35 patients with biopsy-proven thrombotic microangiopathy (the largest in Canada) and 10 patients with C3 glomerulopathy was tested through an extended exome panel to identify causative defects in associated or candidate genes including those of the alternative and terminal complement pathways. A variant of unknown significance was also analyzed for pathogenicity through in vitro studies. To our surprise, the prevalence of known causative or risk-associated variants in either of these cohorts was found to be less than ~ 15% overall. However, the panel used and analyses carried out allowed to identify novel variants of potential clinical significance and a number of candidate genes. The prevalence of known genetic defects in adult-onset aHUS and C3G is thus probably much lower than 30 to 50%. Our results also point towards the importance of investigating diseases of the alternative complement pathway through extended exome panels and in vitro analyses.

Key messages

The alternative complement pathway plays a major role in the pathogenesis of hemolytic uremic syndrome and C3 glomerulopathy.

Based on previous studies, both disorders have been commonly linked to variants in the various intermediates that sustain or regulate this pathway.

The prevalence of such mutations in the adult-onset and sporadic forms of these diseases is probably much lower than expected based on larger series.

The sporadic forms of complementopathies are likely to involve additional genes that are yet to be uncovered.

Supplementary information

The online version contains supplementary material available at 10.1007/s00109-021-02102-1.

Improved Renal Recovery with Eculizumab Therapy among Children with High Prevalence of Mutation-Associated Atypical Hemolytic Uremic Syndrome: A Retrospective Cohort Study

INTRODUCTION

Genetic defects that determine uncontrolled activation of the alternative complement pathway have been well documented, which account for approximately 40-60% of atypical hemolytic uremic syndrome (aHUS) cases worldwide. In Saudi Arabia, nearly half of the marriages are consanguineous, resulting in a high prevalence of such genetic diseases. Recent studies have demonstrated the effectiveness of eculizumab against aHUS.

OBJECTIVE

We report our experience of using plasma therapy or/and eculizumab to treat children with aHUS in a tertiary care center in Saudi Arabia and to compare their clinical characteristics, genetic mutations, and treatment outcomes.

METHODS

A retrospective cohort study was conducted between January 2010 and May 2017. Data, including demographic parameters, clinical presentation, hospital stay duration, need for dialysis, renal recovery, genetic mutations, and outcomes, were obtained from electronic medical records of all eligible patients.

RESULTS

Overall, 21 children with aHUS were included, of which 12 (57.1%) received eculizumab therapy and 9 (42.9%) received only plasma therapy. End-stage renal disease occurred in 7 children (33.3%), of which 4 (57.1%) received only plasma therapy and 3 (42.9%) received eculizumab therapy whose genetic mutations were not related to the complement dysregulation system. No child who received eculizumab therapy showed recurrence; however, 3 children (33.3%) who received plasma therapy alone showed recurrence. Genetic mutations were detected in 12/20 (60%) of those who underwent genetic screening.

CONCLUSIONS

Children who received eculizumab therapy showed good renal recovery and maintained remission compared with children who received plasma therapy alone. Genetic mutations were detected in 60% of the patients, which was associated with a high prevalence of consanguineous marriages.

Broadly effective metabolic and immune recovery with C5 inhibition in CHAPLE disease

Complement hyperactivation, angiopathic thrombosis and protein-losing enteropathy (CHAPLE disease) is a lethal disease caused by genetic loss of the complement regulatory protein CD55, leading to overactivation of complement and innate immunity together with immunodeficiency due to immunoglobulin wasting in the intestine. We report in vivo human data accumulated using the complement C5 inhibitor eculizumab for the medical treatment of patients with CHAPLE disease. We observed cessation of gastrointestinal pathology together with restoration of normal immunity and metabolism. We found that patients rapidly renormalized immunoglobulin concentrations and other serum proteins as revealed by aptamer profiling, re-established a healthy gut microbiome, discontinued immunoglobulin replacement and other treatments and exhibited catch-up growth. Thus, we show that blockade of C5 by eculizumab effectively re-establishes regulation of the innate immune complement system to substantially reduce the pathophysiological manifestations of CD55 deficiency in humans.

A case report of late-onset atypical Hemolytic Uremic Syndrome during interferon beta in multiple sclerosis: Open issues in literature review

BACKGROUND AND AIMS

Interferon beta (IFNβ) is a well-established first-line therapy for relapsing-remitting multiple sclerosis (RRMS) patients and remains the most widely prescribed agent. Atypical hemolytic uremic syndrome (aHUS) represents a rare but severe adverse effect (AE) that could occur even after many years from the beginning of IFNβ therapy. Eculizumab is currently approved for treatment of aHUS and recently for neuromyelitis optica spectrum disorder (NMOSD) with aquaporin-4 antibodies (AQP4-IgG). In this article, we report the case of the latest onset of IFNβ-related aHUS experienced by an MS patient and we briefly review the literature on this topic.

METHODS

We performed a systematic review of the literature using PubMed, and we performed a retrospective analysis of RRMS patients that received IFNβ-1a in our center and developed thrombotic microangiopathy (TMA). From this search, we identified only one patient.

RESULTS

In the published literature, we identified 24 MS patients who received IFNβ as disease-modifying treatment (DMT) and then developed thrombotic microangiopathy with kidney injury. The aHUS has been diagnosed in 6, all received IFNβ-1a and the latest onset was after 15 years. We report a case of a 39-year-old man affected by RRMS who assumed IFNβ-1a since 1999. In July 2018, he developed an IFNβ-related aHUS. After the failure of plasma exchange, he underwent eculizumab, with an improvement of glomerular filtration rate and without new signs of MS activity.

CONCLUSION

To our knowledge, this case represents the latest onset of IFNβ-related aHUS in MS patients. Up to now, there are not literary reports about the possibility to reintroduce a DMT as add-on therapy to eculizumab.

Complement System: a Neglected Pathway in Immunotherapy

Approved for the treatment of autoimmune diseases, hematological malignancies, and solid cancers, several monoclonal antibodies (mAb) make use of complement in their mechanism of action. Such an assessment is based on comprehensive investigations that used mouse models, in vitro studies, and analyses from patients at initiation (basal level to highlight deficiencies) and after treatment initiation (mAb impact on complement), which have further provided key insights into the importance of the complement activation and/or complement deficiencies in mAb activity. Accordingly, new approaches can now be developed with the final objective of increasing the clinical efficacy of mAb. These improvements include (i) the concurrent administration of fresh frozen plasma during mAb therapy; (ii) mAb modifications such as immunoglobulin G subclass switching, Fc mutation, or IgG hexamerization to improve the fixation and activation of C1q; (iii) optimization of the target recognition to induce a higher complement-dependent cytotoxicity (CDC) and/or complement-dependant cellular cytotoxicity (CDCC); and (iv) the control of soluble and cellular complement inhibitors.

Characterizing the original anti-C5 function-blocking antibody, BB5.1, for species specificity, mode of action and interactions with C5

The implication of complement in multiple diseases over the last 20 years has fuelled interest in developing anti-complement drugs. To date, the focus has been on C5; blocking cleavage of C5 prevents formation of two pro-inflammatory activities, C5a anaphylatoxin and membrane attack complex. The concept of C5 blockade to inhibit inflammation dates back 30 years to the description of BB5.1, an anti-C5 blocking monoclonal antibody raised in C5-deficient mice. This antibody proved an invaluable tool to demonstrate complement involvement in mouse disease models and catalysed enthusiasm for anti-complement drug development, culminating in the anti-human C5 monoclonal antibody eculizumab, the most successful anti-complement drug to date, already in clinical use for several rare diseases. Despite its key role in providing proof-of-concept for C5 blockade, the mechanism of BB5.1 inhibition remains poorly understood. Here, we characterized BB5.1 cross-species inhibition, C5 binding affinity and chain specificity. BB5.1 efficiently inhibited C5 in mouse serum but not in human or other rodent sera; it prevented C5 cleavage and C5a generation. BB5.1 bound the C5 α-chain with high affinity and slow off-rate. BB5.1 complementarity-determining regions were obtained and docking algorithms were used to predict the likely binding interface on mouse C5.

Quantification of Factor H Mediated Self vs. Non-self Discrimination by Mathematical Modeling

The complement system is part of the innate immune system and plays an important role in the host defense against infectious pathogens. One of the main effects is the opsonization of foreign invaders and subsequent uptake by phagocytosis. Due to the continuous default basal level of active complement molecules, a tight regulation is required to protect the body's own cells (self cells) from opsonization and from complement damage. A major complement regulator is Factor H, which is recruited from the fluid phase and attaches to cell surfaces where it effectively controls complement activation. Besides self cells, pathogens also have the ability to bind Factor H; they can thus escape opsonization and phagocytosis causing severe infections. In order to advance our understanding of the opsonization process at a quantitative level, we developed a mathematical model for the dynamics of the complement system-termed DynaCoSys model-that is based on ordinary differential equations for cell surface-bound molecules and on partial differential equations for concentration profiles of the fluid phase molecules in the environment of cells. This hybrid differential equation approach allows to model the complement cascade focusing on the role of active C3b in the fluid phase and on the cell surface as well as on its inactivation on the cell surface. The DynaCoSys model enables us to quantitatively predict the conditions under which Factor H mediated complement evasion occurs. Furthermore, investigating the quantitative impact of model parameters by a sensitivity analysis, we identify the driving processes of complement activation and regulation in both the self and non-self regime. The two regimes are defined by a critical Factor H concentration on the cell surface and we use the model to investigate the differential impact of complement model parameters on this threshold value. The dynamic modeling on the surface of pathogens are further relevant to understand pathophysiological situations where Factor H mutants and defective Factor H binding to target surfaces results in pathophysiology such as renal and retinal disease. In the future, this DynaCoSys model will be extended to also enable evaluating treatment strategies of complement-related diseases.

[The experience of using the Russian biosimilar of the original drug eculizumab for the treatment of patients with atypical hemolytic-uremic syndrome]

Atypical hemolytic-uremic syndrome (aHUS) is a chronic systemic disease of a genetic nature, which is based on uncontrolled activation of the alternative complement pathway, leading to generalized thrombosis in the vessels of the microvasculature (complement-mediated thrombotic microangiopathy). To date, therapy with eculizumab is the most effective and pathogenetically substantiated method of treating patients with ASH. Using the example of three clinical cases of patients with a verified diagnosis of aHUS, the high efficiency and safety of the worlds first bioanalogue of eculizumab in the treatment of adult patients with aHUS (complement-mediated thrombotic microangiopathy) was demonstrated.

Innate immunity in diabetic kidney disease

Increasing evidence suggests that renal inflammation contributes to the pathogenesis and progression of diabetic kidney disease (DKD) and that anti-inflammatory therapies might have renoprotective effects in DKD. Immune cells and resident renal cells that activate innate immunity have critical roles in triggering and sustaining inflammation in this setting. Evidence from clinical and experimental studies suggests that several innate immune pathways have potential roles in the pathogenesis and progression of DKD. Toll-like receptors detect endogenous danger-associated molecular patterns generated during diabetes and induce a sterile tubulointerstitial inflammatory response via the NF-κB signalling pathway. The NLRP3 inflammasome links sensing of metabolic stress in the diabetic kidney to activation of pro-inflammatory cascades via the induction of IL-1β and IL-18. The kallikrein-kinin system promotes inflammatory processes via the generation of bradykinins and the activation of bradykinin receptors, and activation of protease-activated receptors on kidney cells by coagulation enzymes contributes to renal inflammation and fibrosis in DKD. In addition, hyperglycaemia leads to protein glycation and activation of the complement cascade via recognition of glycated proteins by mannan-binding lectin and/or dysfunction of glycated complement regulatory proteins. Data from preclinical studies suggest that targeting these innate immune pathways could lead to novel therapies for DKD.

Complement and Complement Targeting Therapies in Glomerular Diseases

The complement cascade is part of the innate immune system whose actions protect hosts from pathogens. Recent research shows complement involvement in a wide spectrum of renal disease pathogenesis including antibody-related glomerulopathies and non-antibody-mediated kidney diseases, such as C3 glomerular disease, atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. A pivotal role in renal pathogenesis makes targeting complement activation an attractive therapeutic strategy. Over the last decade, a growing number of anti-complement agents have been developed; some are approved for clinical use and many others are in the pipeline. Herein, we review the pathways of complement activation and regulation, illustrate its role instigating or amplifying glomerular injury, and discuss the most promising novel complement-targeting therapies.

The Changing Landscape of Acute Kidney Injury in Pregnancy from an Obstetrics Perspective

Pregnancy-related acute kidney injury (PR-AKI) is a heterogeneous disorder with multiple aetiologies that can occur at any time throughout pregnancy and the post-partum period. PR-AKI is an important obstetric complication that is associated with significant maternal and foetal morbidity and mortality. Although there has been an overall decline in the incidence of PR-AKI worldwide, a recent shift in the occurrence of this disease has been reported. Following improvements in obstetric care, PR-AKI incidence has been reduced in developing countries, whereas an increase in PR-AKI incidence has been reported in developed countries. Awareness of the physiological adaptations of the renal system is essential for the diagnosis and management of kidney impairment in pregnancy. In this review we scrutinize the factors that have contributed to the changing epidemiology of PR-AKI and discuss challenges in the diagnosis and management of acute kidney injury (AKI) in pregnancy from an obstetrics perspective. Thereafter we provide brief discussions on the diagnostic approach of certain PR-AKI aetiologies and summarize key therapeutic measures.

Development and characterization of novel anti-C5 monoclonal antibodies capable of inhibiting complement in multiple species

Over the last decade there has been an explosion in complement therapies; one-third of the drugs in the clinic or in development target C5 protein. Eculizumab, a monoclonal antibody (mAb) that binds C5 and blocks its cleavage by the convertase, is the current reference standard treatment for atypical haemolytic uraemic syndrome (aHUS) and paroxysmal nocturnal haemoglobinuria (PNH) and in clinical trials for many other diseases. Here we describe a panel of novel anti-C5 mAb, including mAb that, like Eculizumab, are efficient inhibitors of complement but, unlike Eculizumab, inhibit across species, including human, rat, rabbit and guinea pig. Several inhibitory anti-C5 mAb were identified and characterized for C5 binding and lytic inhibitory capacity in comparison to current therapeutic anti-C5 mAb; three clones, 4G2, 7D4 and 10B6, were selected and further characterized for ligand specificity and affinity and cross-species inhibitory activity. The mAb 10B6 was human-specific whereas mAb 4G2 and 7D4 efficiently inhibited lysis by human, rabbit and rat serum, and weakly inhibited guinea pig complement; 7D4 also weakly inhibited mouse complement in vitro The rat C5-cross-reactive mAb 4G2, when administered intraperitoneally in a rat model of myasthenia gravis, effectively blocked the disease and protected muscle endplates from destruction. To our knowledge this is the first report of an anti-C5 function blocking mAb that permits preclinical studies in rats.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

New concepts on the therapeutic control of complement anaphylatoxin receptors

The complement system is a pivotal driver of innate immunity, coordinating the host response to protect against pathogens. At the heart of the complement response lie the active fragments, C3a and C5a, acting through their specific receptors, C3aR, C5aR1, and C5aR2, to direct the cellular response to inflammation. Their potent function however, places them at risk of damaging the host, with aberrant C3a and C5a signaling activity linked to a wide range of disorders of inflammatory, autoimmune, and neurodegenerative etiologies. As such, the therapeutic control of these receptors represents an attractive drug target, though, the realization of this clinical potential remains limited. With the success of eculizumab, and the progression of a number of novel C5a-C5aR1 targeted drugs to phase II and III clinical trials, there is great promise for complement therapeutics in future clinical practice. In contrast, the toolbox of drugs available to modulate C3aR and C5aR2 signaling remains limited, however, the emergence of new selective ligands and molecular tools, and an increased understanding of the function of these receptors in disease, has highlighted their unique potential for clinical applications. This review provides an update on the growing arsenal of drugs now available to target C5, and C5a and C3a receptor signaling, and discusses their utility in both clinical and pre-clinical development.

Rare genetic variant in the CFB gene presenting as atypical hemolytic uremic syndrome and immune complex diffuse membranoproliferative glomerulonephritis, with crescents, successfully treated with eculizumab

BACKGROUND

Complement factor B gene (CFB) is an important component of the alternate pathway of complement activation that provides an active subunit that associates with C3b to form the C3 convertase, which is an essential element in complement activation. Among the complement-associated disorders, mutations and pathogenic variants in the CFB gene are relatively rare phenomena. Moreover, mutated CFB affiliation with immune-complex diffuse membranoproliferative glomerulonephritis (IC-MPGN) and atypical hemolytic uremic syndrome (aHUS) are considered a highly rare occurrence.

CASE PRESENTATION

We describe the clinical presentation, course, and pathological findings in a 7-year-old boy who has confirmed CFB heterozygous variants with pathological features compatible with IC-MPGN. Mutational analysis revealed a heterozygous variant p.Glu566Arg in exon 13 of the CFB gene. The patient did not respond to steroids and mycophenolate mofetil (MMF) therapy but responded clinically and biochemically to eculizumab treatment. This is the first case report of CFB alteration associated with IC-MPGN and aHUS that was successfully treated with eculizumab.

CONCLUSIONS

Heterozygous variants in the CFB gene can be pathogenic and associated with IC-MPGN and aHUS. Early diagnosis and prompt management can be essential in preventing end-stage renal disease. Eculizumab may provide an effective modality of treatment.

Potential influences of complement factor H in autoimmune inflammatory and thrombotic disorders

Complement system homeostasis is important for host self-protection and anti-microbial immune surveillance, and recent research indicates roles in tissue development and remodelling. Complement also appears to have several points of interaction with the blood coagulation system. Deficiency and altered function due to gene mutations and polymorphisms in complement effectors and regulators, including Factor H, have been associated with familial and sporadic autoimmune inflammatory - thrombotic disorders, in which autoantibodies play a part. These include systemic lupus erythematosus, rheumatoid arthritis, atypical haemolytic uremic syndrome, anti-phospholipid syndrome and age-related macular degeneration. Such diseases are generally complex - multigenic and heterogeneous in their symptoms and predisposition/susceptibility. They usually need to be triggered by vascular trauma, drugs or infection and non-complement genetic factors also play a part. Underlying events seem to include decline in peripheral regulatory T cells, dendritic cell, and B cell tolerance, associated with alterations in lymphoid organ microenvironment. Factor H is an abundant protein, synthesised in many cell types, and its reported binding to many different ligands, even if not of high affinity, may influence a large number of molecular interactions, together with the accepted role of Factor H within the complement system. Factor H is involved in mesenchymal stem cell mediated tolerance and also contributes to self-tolerance by augmenting iC3b production and opsonisation of apoptotic cells for their silent dendritic cell engulfment via complement receptor CR3, which mediates anti-inflammatory-tolerogenic effects in the apoptotic cell context. There may be co-operation with other phagocytic receptors, such as complement C1q receptors, and the Tim glycoprotein family, which specifically bind phosphatidylserine expressed on the apoptotic cell surface. Factor H is able to discriminate between self and nonself surfaces for self-protection and anti-microbe defence. Factor H, particularly as an abundant platelet protein, may also modulate blood coagulation, having an anti-thrombotic role. Here, we review a number of interaction pathways in coagulation and in immunity, together with associated diseases, and indicate where Factor H may be expected to exert an influence, based on reports of the diversity of ligands for Factor H.

Complements Spurned: Our Experience with Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder resulting from a dysregulated activation of the alternative pathway of the complement system. It results in significant morbidity and mortality if not diagnosed and treated promptly. It lends itself to myriad renal and extrarenal manifestations, all potentially disabling. Eculizumab, a monoclonal antibody to complement C5 is now the widely accepted norm for treatment. However, in resource-limited settings, plasma exchange if instituted early may be as beneficial. We report a case of aHUS treated with extended plasma exchange with excellent results. Critical care monitoring is essential for the management of the disease in view of a tendency to develop multiple complications. Long-term immunosuppression may be successful in maintaining remission.

A Case Report and Literature Review of Eculizumab Withdrawal in Atypical Hemolytic-Uremic Syndrome

BACKGROUND Recent advances in the treatment of atypical hemolytic-uremic syndrome (aHUS) have resulted to better long-term survival rates for patients with this life-threatening disease. However, many questions remain such as whether or not long-term treatment is necessary in some patients and what are the risks of prolonged therapy. CASE REPORT Here, we discuss the case of a 37-year-old woman with CFH and CD46 genetic abnormalities who developed aHUS with severe renal failure. She was successfully treated with three doses of rituximab and a three month treatment with eculizumab. After eculizumab withdrawal, symptoms of thrombotic micro-angiopathy (TMA) recurred, therefore eculizumab treatment was restarted. The patient exhibited normal renal function and no symptoms of aHUS at one-year follow-up with further eculizumab treatment. CONCLUSIONS This case highlights the clinical challenges of the diagnosis and management of patient with aHUS with complement-mediated TMA involvement. Attention was paid to the consequences of the treatment withdrawal. Exact information regarding genetic abnormalities and renal function associated with aHUS, as well as estimations of the relapse risk and monitoring of complement tests may provide insights into the efficacy of aHUS treatment, which will enable the prediction of therapeutic responses and testing of new treatment options. Improvements in our understanding of aHUS and its causes may facilitate the identification of patients in whom anti-complement therapies can be withdrawn without risk.

Complement: A primer for the coming therapeutic revolution

The complement system is an important part of the innate and adaptive immune systems. Originally characterized as a single serum component contributing to the killing of bacteria, we now know that there are close to sixty complement proteins, multiple activation pathways and a wide range of effector functions mediated by complement. The system plays a critical role in host defense against bacteria, viruses, fungi and other pathogens. However, inappropriate complement activation contributes to the pathophysiology of autoimmune diseases and many inflammatory syndromes. Over the last several decades, therapeutic approaches to inhibit complement activation at various steps in the pathways have met with initial success, particularly at the level of the terminal pathway. This success, combined with insight from animal model studies, has lead to an unprecedented effort by biotech and pharmaceutical companies to begin developing complement inhibitors. As a result, complement has been brought for the first time to the attention of pharmacologists, toxicologists, project managers and others in the drug development industry, as well as those in the investment world. The purpose of this primer is to provide a broad overview of complement immunobiology to help those new to complement understand the rationale behind the current therapeutic directions and the investment potential of these new therapeutics.

Monitoring of complement activation biomarkers and eculizumab in complement-mediated renal disorders

Various complement-mediated renal disorders are treated currently with the complement inhibitor eculizumab. By blocking the cleavage of C5, this monoclonal antibody prevents cell damage caused by complement-mediated inflammation. We included 23 patients with atypical haemolytic uraemic syndrome (aHUS, n = 12), C3 glomerulopathies (C3G, n = 9) and acute antibody-mediated renal graft rejection (AMR, n = 2), treated with eculizumab in 12 hospitals in Germany. We explored the course of complement activation biomarkers and the benefit of therapeutic drug monitoring of eculizumab. Complement activation was assessed by analysing the haemolytic complement function of the classical (CH50) and the alternative pathway (APH50), C3 and the activation products C3d, C5a and sC5b-9 prior to, 3 and 6 months after eculizumab treatment. Eculizumab concentrations were determined by a newly established specific enzyme-linked immunosorbent assay (ELISA). Serum eculizumab concentrations up to 1082 μg/ml point to drug accumulation, especially in paediatric patients. Loss of the therapeutic antibody via urine with concentrations up to 56 μg/ml correlated with proteinuria. In aHUS patients, effective complement inhibition was demonstrated by significant reductions of CH50, APH50, C3d and sC5b-9 levels, whereas C5a levels were only reduced significantly after 6 months' treatment. C3G patients presented increased C3d and consistently low C3 levels, reflecting ongoing complement activation and consumption at the C3 level, despite eculizumab treatment. A comprehensive complement analysis together with drug monitoring is required to distinguish mode of complement activation and efficacy of eculizumab treatment in distinct renal disorders. Accumulation of the anti-C5 antibody points to the need for a patient-orientated tailored therapy.

PEGylated Artificial Antibodies: Plasmonic Biosensors with Improved Selectivity

Molecular imprinting, which involves the formation of artificial recognition elements or cavities with complementary shape and chemical functionality to the target species, is a powerful method to overcome a number of limitations associated with natural antibodies. An important but often overlooked consideration in the design of artificial biorecognition elements based on molecular imprinting is the nonspecific binding of interfering species to noncavity regions of the imprinted polymer. Here, we demonstrate a universal method, namely, PEGylation of the noncavity regions of the imprinted polymer, to minimize the nonspecific binding and significantly enhance the selectivity of the molecular imprinted polymer for the target biomolecules. The nonspecific binding, as quantified by the localized surface plasmon resonance shift of imprinted plasmonic nanorattles upon exposure to common interfering proteins, was found to be more than 10 times lower compared to the non-PEGylated counterparts. The method demonstrated here can be broadly applied to a wide variety of functional monomers employed for molecular imprinting. The significantly higher selectivity of PEGylated molecular imprints takes biosensors based on these artificial biorecognition elements closer to real-world applications.

The relative merits of therapies being developed to tackle inappropriate ('self'-directed) complement activation

The complement system is an enzyme cascade that helps defend against infection. Many complement proteins occur in serum as inactive enzyme precursors or reside on cell surfaces. Complement components have many biologic functions and their activation can eventually damage the plasma membranes of cells and some bacteria. Although a direct link between complement activation and autoimmune diseases has not been found, there is increasing evidence that complement activation significantly contributes to the pathogenesis of a large number of inflammatory diseases that may have autoimmune linkage. The inhibition of complement may therefore be very important in a variety of autoimmune diseases since their activation may be detrimental to the individual involved. However, a complete and long-term inhibition of complement may have some contra side effects such as increased susceptibility to infection. The site of complement activation will, however, determine the type of inhibitor to be used, its route of application and dosage level. Compared with conventional drugs, complement inhibitors may be the best option for treatment of autoimmune diseases. The review takes a critical look at the relative merits of therapies being developed to tackle inappropriate complement activation that are likely to result in sporadic autoimmune diseases or worsen already existing one. It covers the complement system, general aspects of complement inhibition therapy, therapeutic strategies and examples of complement inhibitors. It concludes by highlighting on the possibility that a better inhibitor of complement activation when found will help provide a formidable treatment for autoimmune diseases as well as preventing one.

Progress with the use of monoclonal antibodies for the treatment of systemic lupus erythematosus

In recent years, significant progress has been made in the use of monoclonal antibodies in the treatment of systemic lupus erythematosus (SLE). Advances in our understanding of the complexity of SLE immunopathogenesis have led to the testing of several biologic agents in clinical trials. Monoclonal therapies currently emerging or under development include B-cell depletion therapies, agents targeting B-cell survival factors, blockade of T-cell co-stimulation and anticytokine therapies. Issues remain, however, regarding clinical trial design and outcome measures in SLE which need to be addressed to optimize translation of these promising therapies into clinical practice.

An international consensus approach to the management of atypical hemolytic uremic syndrome in children

Atypical hemolytic uremic syndrome (aHUS) emerged during the last decade as a disease largely of complement dysregulation. This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab). We review treatment and patient management issues related to this therapeutic approach. We present consensus clinical practice recommendations generated by HUS International, an international expert group of clinicians and basic scientists with a focused interest in HUS. We aim to address the following questions of high relevance to daily clinical practice: Which complement investigations should be done and when? What is the importance of anti-factor H antibody detection? Who should be treated with eculizumab? Is plasma exchange therapy still needed? When should eculizumab therapy be initiated? How and when should complement blockade be monitored? Can the approved treatment schedule be modified? What approach should be taken to kidney and/or combined liver-kidney transplantation? How should we limit the risk of meningococcal infection under complement blockade therapy? A pressing question today regards the treatment duration. We discuss the need for prospective studies to establish evidence-based criteria for the continuation or cessation of anticomplement therapy in patients with and without identified complement mutations.

An international consensus approach to the management of atypical hemolytic uremic syndrome in children

Atypical hemolytic uremic syndrome (aHUS) emerged during the last decade as a disease largely of complement dysregulation. This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab). We review treatment and patient management issues related to this therapeutic approach. We present consensus clinical practice recommendations generated by HUS International, an international expert group of clinicians and basic scientists with a focused interest in HUS. We aim to address the following questions of high relevance to daily clinical practice: Which complement investigations should be done and when? What is the importance of anti-factor H antibody detection? Who should be treated with eculizumab? Is plasma exchange therapy still needed? When should eculizumab therapy be initiated? How and when should complement blockade be monitored? Can the approved treatment schedule be modified? What approach should be taken to kidney and/or combined liver-kidney transplantation? How should we limit the risk of meningococcal infection under complement blockade therapy? A pressing question today regards the treatment duration. We discuss the need for prospective studies to establish evidence-based criteria for the continuation or cessation of anticomplement therapy in patients with and without identified complement mutations.

Complement activation patterns in atypical haemolytic uraemic syndrome during acute phase and in remission

Atypical haemolytic uraemic syndrome (aHUS) is associated with (genetic) alterations in alternative complement pathway. Nevertheless, comprehensive evidence that the complement system in aHUS patients is more prone to activation is still lacking. Therefore, we performed a thorough analysis of complement activation in acute phase and in remission of this disease. Complement activation patterns of the aHUS patients in acute phase and in remission were compared to those of healthy controls. Background levels of complement activation products C3b/c, C3bBbP and terminal complement complex (TCC) were measured using enzyme-linked immunosorbent assay (ELISA) in ethylenediamine tetraacetic acid (EDTA) plasma. In vitro-triggered complement activation in serum samples was studied using zymosan-coating and pathway-specific assay. Furthermore, efficiencies of the C3b/c, C3bBbP and TCC generation in fluid phase during spontaneous activation were analysed. Patients with acute aHUS showed elevated levels of C3b/c (P < 0·01), C3bBbP (P < 0·0001) and TCC (P < 0·0001) in EDTA plasma, while values of patients in remission were normal, compared to those of healthy controls. Using data from a single aHUS patient with complement factor B mutation we illustrated normalization of complement activation during aHUS recovery. Serum samples from patients in remission showed normal in vitro patterns of complement activation and demonstrated normal kinetics of complement activation in the fluid phase. Our data indicate that while aHUS patients have clearly activated complement in acute phase of the disease, this is not the case in remission of aHUS. This knowledge provides important insight into complement regulation in aHUS and may have an impact on monitoring of these patients, particularly when using complement inhibition therapy.

Case report: Benefits and challenges of long-term eculizumab in atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is caused by dysregulation of the complement system, leading to complement overactivation. A humanized anti-C5 monoclonal antibody, eculizumab, has been available for the treatment of aHUS since 2011. The long-term safety and efficacy of this novel drug in the pediatric population remain under review. We present a child with a hybrid CFH/CFHR3 gene who, having had multiple disease relapses despite optimal treatment with plasma exchange, commenced eculizumab therapy in August 2010. She remains relapse free in follow-up at 52 months, and treatment has been well tolerated. The risk of meningococcal disease during this treatment is recognized. Despite vaccination against meningococcal disease and appropriate antibiotic prophylaxis, our patient developed meningococcal bacteremia 30 months into treatment. She presented with nonspecific symptoms but recovered without sequelae with appropriate treatment. We recommend that children be vaccinated against invasive meningococcal infection before beginning eculizumab therapy and take appropriate antibiotic prophylaxis during treatment, and we suggest that vaccine responses should be checked and followed annually. Clinicians need to maintain a high index of suspicion for invasive meningococcal disease. Neither vaccination nor antibiotic prophylaxis provides complete protection in patients on eculizumab therapy. The appropriate dosage of eculizumab needed to achieve remission in aHUS in the pediatric population is unknown. Having achieved remission in our patient, we monitor eculizumab and CH50 levels to evaluate ongoing blockade of the terminal complement cascade. Such information may help guide dosing intervals in the future.

Success of eculizumab in the treatment of atypical hemolytic uremic syndrome

BACKGROUND

Disorders of complement regulation are the most important etiology of atypical hemolytic uremic syndrome (aHUS). Recent studies demonstrate that eculizumab is beneficial in long-term aHUS treatment. We present a series of children with aHUS resistant to/dependent on plasma exchange (PE) who were treated with eculizumab.

METHODS

This was a retrospective study in which data were retrieved from the medical files of children who had received PE as treatment for aHUS. The data retrieved included age, sex, presenting symptoms, presence of diarrhea/vomiting, hospitalization duration, laboratory data on admission and follow-up, need for transfusion or dialysis, response to PE, response to eculizumab and outcome.

RESULTS

Of the 15 children diagnosed with aHUS in 2011 and 2012 in our departments, ten were resistant to, or dependent on, plasma therapy and treated with eculizumab; these children were enrolled in the study. Three patients had relapses, and seven had a new diagnosis. Nine children had oliguria or anuria, and eight required dialysis. Hypertension was observed in six patients. Neurologic involvement developed in six patients, with the symptoms including seizures, loss of balance, vision loss and severe confusion. Five and five patients were resistant to and dependent on plasma therapy, respectively. Following the start of eculizumab treatment, all patients achieved full recovery of renal function and hematologic parameters.

CONCLUSIONS

In our ten pediatric patients with aHUS who did not respond to PE, eculizumab was a lifesaving therapy and improved their quality of life. Early eculizumab use was a rescue therapy for renal function. Our results show that eculizumab is an effective treatment for aHUS. However, more studies are needed on the long-term efficacy and safety of eculizumab in children with aHUS and to determine the optimal duration of treatment.

Plasma resistant atypical hemolytic uremic syndrome associated with a CFH mutation treated with eculizumab: a case report

Introduction

Thrombotic microangiopathies are a group of diseases presenting as microangiopathic hemolytic anemia, thrombocytopenia and end-organ dysfunction. As the role of the complement system was elucidated in atypical hemolytic uremic syndrome pathogenesis, eculizumab was successfully introduced into clinical practice. We present a large pedigree with multiple individuals carrying a functionally significant novel factor H mutation. We describe the proband’s presentation following a presumed infectious trigger requiring plasma exchange and hemodialysis.

Case presentation

A 32-year-old Caucasian woman presented with pyrexia and headache lasting one week to our Emergency Department. She gave no history of diarrhea or other symptoms to account for her high temperature. She was not taking any medication. She was pyrexial (38°C), tachycardic (110bpm) and hypertensive (160/110mmHg). Her fundoscopy revealed grade IV hypertensive retinopathy. She had mild pretibial and periorbital edema, with oliguria (450mL/day). She had a pregnancy one year previously, during which she had hypertension, proteinuria and edema, with successful delivery at term. Her mother had died in her early 30s with a clinical picture consistent with thrombotic microangiopathy. Her laboratory evaluation showed microangiopathic hemolytic anemia. After 22 sessions of plasma exchange, her lactate dehydrogenase levels started to climb. As a result, she was classified as plasma resistant and eculizumab therapy was instituted. Her lactate dehydrogenase level and platelet count normalized, and her renal function recovered after three months of dialysis.

Conclusions

We demonstrate that, even in patients with atypical hemolytic uremic syndrome and prolonged dialysis dependence, recovery of renal function can be seen with eculizumab treatment. We suggest a treatment regime of at least three months prior to evaluation of efficacy.

Rare genetic variants in the CFI gene are associated with advanced age-related macular degeneration and commonly result in reduced serum factor I levels

To assess a potential diagnostic and therapeutic biomarker for age-related macular degeneration (AMD), we sequenced the complement factor I gene (CFI) in 2266 individuals with AMD and 1400 without, identifying 231 individuals with rare genetic variants. We evaluated the functional impact by measuring circulating serum factor I (FI) protein levels in individuals with and without rare CFI variants. The burden of very rare (frequency <1/1000) variants in CFI was strongly associated with disease (P = 1.1 × 10⁻⁸). In addition, we examined eight coding variants with counts ≥5 and saw evidence for association with AMD in three variants. Individuals with advanced AMD carrying a rare CFI variant had lower mean FI compared with non-AMD subjects carrying a variant (P < 0.001). Further new evidence that FI levels drive AMD risk comes from analyses showing individuals with a CFI rare variant and low FI were more likely to have advanced AMD (P = 5.6 × 10⁻⁵). Controlling for covariates, low FI increased the risk of advanced AMD among those with a variant compared with individuals without advanced AMD with a rare CFI variant (OR 13.6, P = 1.6 × 10⁻⁴), and also compared with control individuals without a rare CFI variant (OR 19.0, P = 1.1 × 10⁻⁵). Thus, low FI levels are strongly associated with rare CFI variants and AMD. Enhancing FI activity may be therapeutic and measuring FI provides a screening tool for identifying patients who are most likely to benefit from complement inhibitory therapy.

Complement in therapy and disease: Regulating the complement system with antibody-based therapeutics

Complement is recognized as a key player in a wide range of normal as well as disease-related immune, developmental and homeostatic processes. Knowledge of complement components, structures, interactions, and cross-talk with other biological systems continues to grow and this leads to novel treatments for cancer, infectious, autoimmune- or age-related diseases as well as for preventing transplantation rejection. Antibodies are superbly suited to be developed into therapeutics with appropriate complement stimulatory or inhibitory activity. Here we review the design, development and future of antibody-based drugs that enhance or dampen the complement system.

Spectrum and management of complement immunodeficiencies (excluding hereditary angioedema) across Europe

INTRODUCTION

Complement immunodeficiencies (excluding hereditary angioedema and mannose binding lectin deficiency) are rare. Published literature consists largely of case reports and small series. We collated data from 18 cities across Europe to provide an overview of primarily homozygous, rather than partial genotypes and their impact and management.

METHODS

Patients were recruited through the ESID registry. Clinical and laboratory information was collected onto standardized forms and analyzed using SPSS software.

RESULTS

Seventy-seven patients aged 1 to 68 years were identified. 44 % presented in their first decade of life. 29 % had C2 deficiency, defects in 11 other complement factors were found. 50 (65 %) had serious invasive infections. 61 % of Neisseria meningitidis infections occurred in patients with terminal pathway defects, while 74 % of Streptococcus pneumoniae infections occurred in patients with classical pathway defects (p < 0.001). Physicians in the UK were more likely to prescribe antibiotic prophylaxis than colleagues on the Continent for patients with classical pathway defects. After diagnosis, 16 % of patients suffered serious bacterial infections. Age of the patient and use of prophylactic antibiotics were not associated with subsequent infection risk. Inflammatory/autoimmune diseases were not seen in patients with terminal pathway, but in one third of patients classical and alternative pathway defects.

CONCLUSION

The clinical phenotypes of specific complement immunodeficiencies vary considerably both in terms of the predominant bacterial pathogen, and the risk and type of auto-inflammatory disease. Appreciation of these phenotypic differences should help both immunologists and other specialists in their diagnosis and management of these rare and complex patients.

Anticomplement C5 therapy with eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome

The complement inhibitor eculizumab is a humanized monoclonal antibody against C5. It was developed to specifically target cleavage of C5 thus preventing release of C5a and activation of the terminal pathway. Paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) are 2 diseases with distinctly different underlying molecular mechanisms. In PNH, progeny of hematopoietic stem cells that harbor somatic mutations lead to a population of peripheral blood cells that are deficient in complement regulators resulting in hemolysis and thrombosis. In aHUS, germline mutations in complement proteins or their regulators fail to protect the glomerular endothelium from complement activation resulting in thrombotic microangiopathy and renal failure. Critical to the development of either disease is activation of the terminal complement pathway. Understanding this step has led to the study of eculizumab as a treatment for these diseases. In clinical trials, eculizumab is proven to be effective and safe in PNH and aHUS.

Autoantibodies to CD59, CD55, CD46 or CD35 are not associated with atypical haemolytic uraemic syndrome (aHUS)

Autoantibody formation against Factor H (FH) is found in 7-10% of patients who are diagnosed with atypical haemolytic uraemic syndrome (aHUS). These autoantibodies predominately target the C-terminal cell binding recognition domain of FH and are associated with absence of FHR1. Additional autoantibodies have also been identified in association with aHUS, for example autoantibodies to Factor I. Based on this, and that there are genetic mutations in other complement regulators and activators associated with aHUS, we hypothesised that other complement regulator proteins, particularly surface bound regulators in the kidney, might be the target for autoantibody formation in aHUS. Therefore, we assayed serum derived from 89 patients in the Newcastle aHUS cohort for the presence of autoantibodies to CD46 (membrane cofactor protein, MCP), CD55 (decay accelerating factor, DAF), CD35 (complement receptor type 1, CR1; TP10) and CD59. We also assayed 100 healthy blood donors to establish the normal levels of reactivity towards these proteins in the general population. Recombinant proteins CD46 and CD55 (purified from Escherichia coli) as well as soluble CR1 (CD35) and oligomeric C4BP-CD59 (purified from eukaryotic cell media) were used in ELISA to detect high responders. False positive results were established though Western blot and flow cytometric analysis. After excluding false positive responders to bacterial proteins in the CD46 and CD55 preparations, and responses to blood group antigens in CD35, we found no significant level of patient serum IgG reactivity with CD46, CD55, CD35 or CD59 above that detected in the normal population. These results suggest that membrane anchored complement regulators are not a target for autoantibody generation in aHUS.

Atypical hemolytic uremic syndrome: from diagnosis to treatment

Thrombotic microangiopathy (TMA) is a relatively rare condition but a medical urgency requiring immediate intervention to avoid irreversible organ damage or death. Symptoms on presentation include microangiopathic haemolytic anaemia, thrombocytopenia and organ damage. The most frequent direct causes of TMA are thrombotic thrombocytopenic purpura (TTP) and haemolytic uremic syndrome (HUS). The most common form of HUS is related to Shiga toxin producing