Measuring total classical pathway and activities of individual components of the mouse complement pathway

The complement system is a central component of innate immunity, responsible for recognition and killing of bacteria by tagging invaders through opsonisation, thereby promoting phagocytosis, and by direct lysis. Complement activity is routinely measured using functional assays that utilise erythrocytes as targets. The classical pathway haemolytic assay (CH50) with antibody sensitised sheep erythrocytes as target is used worldwide in clinical and research laboratories to measure complement activity in human and rodent sera. While there are no particular limitations in the human assay, measuring complement in mouse serum is more difficult and usually requires large amounts of serum, which is challenging to collect in experiments. In particular, it is challenging to measure the activities of individual mouse complement proteins. To overcome this hurdle, we have developed protocols that employ human sera depleted of single complement proteins as the source of the other complement proteins and test mouse serum to restore the relevant component. This simple haemolytic assay is a useful tool for confirming natural or engineered complement deficiencies and complement dysregulation in mouse models

Targeting the terminal pathway in complement – driven disease.

Objectives; In the last decade there has been an explosion of interest in inhibiting complement for therapy of disease; the principle target has been complement component C5, activation of which generates the pro-inflammatory and cytotoxic products C5a and the membrane attack complex. The anti-C5 monoclonal antibody Eculizumab is a blockbuster drug, currently only approved for two ultra-rare diseases. There is abundant evidence that complement, and specifically the membrane attack complex, is involved in more common diseases for example in age related macular degeneration, myasthenia gravis and neurological disorders like neuromyelitis optica spectrum disorder and multiple sclerosis. Hence, there is an urgent need to develop better, cheaper drugs targeting membrane attack complex. Here I describe novel monoclonal antibodies targeting membrane attack complex downstream of C5 that are efficient inhibitors of its formation in humans and rodents. Methods; A large panel of anti-membrane attack complex monoclonals was generated from spleens of terminal pathway deficient mice hyperimmunised with human or rat C5b6 and/or C5b67. Antibody clones were screened using immunochemical and novel functional (haemolytic) assays to identify those with binding and blocking activities. Biophysical methods, including surface plasmon resonance were used to characterise monoclonal antibodies of interest, and selected antibodies were tested in rodents to characterise pharmacokinetics and therapeutic capacity in complement-mediated disease models. Results; Several function inhibitory anti-membrane attack complex antibodies were identified and characterised in terms of binding to membrane attack complex intermediates and cross-species lytic inhibitory capacity in comparison to current therapeutic anti-C5 monoclonal antibody. Blocking antibody selected include three against C5, two against C6 and five against C7; these efficiently inhibited lysis by human, rat, or mouse serum in vitro and were further characterised for binding specificity and affinity by enzyme linked immunosorbent assay, western blot and surface plasmone resonance, confirming strong and stable binding. One antibody has so far been tested in vivo; administration of this antibody intraperitoneally in rats efficiently inhibited serum lytic activity and blocked the disease and protected muscle endplates from destruction in a rat model of myasthenia gravis. Conclusions; I report novel blocking antibodies that target membrane attack complex formation at different stages of the pathway to efficiently inhibit complement terminal pathway across species (human, rat and mouse). Rodents treated with selected antibody were protected in a complement-driven disease model. These antibodies offer an alternative to C5 targeting for membrane attack complex-driven pathologies in animal models and man and add new data on membrane attack complex assembly and function

Complement and COVID-19: Three years on, what we know, what we don't know, and what we ought to know

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus was identified in China in 2019 as the causative agent of COVID-19, and quickly spread throughout the world, causing over 7 million deaths, of which 2 million occurred prior to the introduction of the first vaccine. In the following discussion, while recognising that complement is just one of many players in COVID-19, we focus on the relationship between complement and COVID-19 disease, with limited digression into directly-related areas such as the relationship between complement, kinin release, and coagulation. Prior to the 2019 COVID-19 outbreak, an important role for complement in coronavirus diseases had been established. Subsequently, multiple investigations of patients with COVID-19 confirmed that complement dysregulation is likely to be a major driver of disease pathology, in some, if not all, patients. These data fuelled evaluation of many complement-directed therapeutic agents in small patient cohorts, with claims of significant beneficial effect. As yet, these early results have not been reflected in larger clinical trials, posing questions such as who to treat, appropriate time to treat, duration of treatment, and optimal target for treatment. While significant control of the pandemic has been achieved through a global scientific and medical effort to comprehend the etiology of the disease, through extensive SARS-CoV-2 testing and quarantine measures, through vaccine development, and through improved therapy, possibly aided by attenuation of the dominant strains, it is not yet over. In this review, we summarise complement-relevant literature, emphasise its main conclusions, and formulate a hypothesis for complement involvement in COVID-19. Based on this we make suggestions as to how any future outbreak might be better managed in order to minimise impact on patients

Targeting complement in neurodegeneration: challenges, risks, and strategies

For most neurodegenerative diseases (NDDs), therapeutic options are limited, providing symptomatic benefit but not impacting disease progression; new treatments addressing critical effectors in the disease process are needed. Evidence implicating complement in NDDs has accumulated over the past two decades, establishing complement dysregulation as a driver of pathology and a novel target for therapy in these diseases. Over the same period, highly effective anticomplement drugs have been developed for therapy of complement dysregulation; however, their use to date has been restricted to rare systemic diseases. Current anticomplement drugs are not fit for purpose in most NDDs because they do not adequately access the central nervous system (CNS). Blood–brain barrier-penetrant anticomplement drugs, created either by modifying current drugs or by designing new drugs, could suppress complement dysregulation, neuroinflammation, and neurodegeneration to halt or slow disease progression. Inhibition of complement is not without risk; this might be particularly the case in the CNS and requires close attention

Monoclonal antibodies capable of inhibiting complement downstream of C5 in multiple species

Better understanding of roles of complement in pathology has fuelled an explosion of interest in complement-targeted therapeutics. The C5-blocking monoclonal antibody (mAb) eculizumab, the first of the new wave of complement blocking drugs, was FDA approved for treatment of Paroxysmal Nocturnal Hemoglobinuria in 2007; its expansion into other diseases has been slow and remains restricted to rare and ultra-rare diseases such as atypical hemolytic uremic syndrome. The success of eculizumab has provoked other Pharma to follow this well-trodden track and made C5 blockade the busiest area of complement drug development. C5 blockade inhibits generation of C5a and C5b, the former an anaphylatoxin, the latter the nidus for formation of the pro-inflammatory membrane attack complex. In order to use anti-complement drugs in common complement-driven diseases, more affordable and equally effective therapeutics are needed. To address this, we explored complement inhibition downstream of C5. Novel blocking mAbs targeting C7 and/or the C5b-7 complex were generated, identified using high throughput functional assays and specificity confirmed by immunochemical assays and surface plasmon resonance (SPR). Selected mAbs were tested in rodents to characterize pharmacokinetics, and therapeutic capacity. Administration of a mouse C7-selective mAb to wildtype mice, or a human C7 specific mAb to C7-deficient mice reconstituted with human C7, completely inhibited serum lytic activity for >48 h. The C5b-7 complex selective mAb 2H2, most active in rat serum, efficiently inhibited serum lytic activity in vivo for over a week from a single low dose (10 mg/kg); this mAb effectively blocked disease and protected muscle endplates from destruction in a rat myasthenia model. Targeting C7 and C7-containing terminal pathway intermediates is an innovative therapeutic approach, allowing lower drug dose and lower product cost, that will facilitate the expansion of complement therapeutics to common diseases

Extracting the barbs from complement assays: Identification and optimisation of a safe substitute for traditional buffers

Complement assays have for many years utilised buffers based on barbitone (veronal) despite the well-recognised toxicity of this agent and the tight regulations on its use in most countries. The use of barbitone in complement assay buffers is steeped in history, from a time when no other suitable buffers were available. This is no longer the case, encouraging us to explore alternatives to barbitone for complement assays. We compared a simple, non-toxic HEPES buffer with commercially sourced complement fixation test diluent (CFD), the “gold standard” barbitone buffer, in several clinically relevant complement activity assays and across species. In classical pathway haemolysis assays in human and non-human serum, there was no difference in haemolytic curves or calculated haemolytic activity (CH50) between CFD and an optimised HEPES buffer (HBS) supplemented with cations. Alternative pathway haemolysis assays in human serum were also identical in the two buffers. In a complement fixation test for anti-erythrocyte antibodies, complement consumption was identical for the two buffer systems. The data demonstrate that barbitone-based buffers are unnecessary for assays of complement activity and can readily be replaced with safe and simple alternatives

Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia

Complement is dysregulated in the brain in Alzheimer’s Disease and in mouse models of Alzheimer’s disease. Each of the complement derived effectors, opsonins, anaphylatoxins and membrane attack complex (MAC), have been implicated as drivers of disease but their relative contributions remain unclarified. Here we have focussed on the MAC, a lytic and pro-inflammatory effector, in the AppNL−G−F mouse amyloidopathy model. To test the role of MAC, we back-crossed to generate AppNL−G−F mice deficient in C7, an essential MAC component. C7 deficiency ablated MAC formation, reduced synapse loss and amyloid load and improved cognition compared to complement-sufficient AppNL−G−F mice at 8–10 months age. Adding back C7 caused increased MAC formation in brain and an acute loss of synapses in C7-deficient AppNL−G−F mice. To explore whether C7 was a viable therapeutic target, a C7-blocking monoclonal antibody was administered systemically for one month in AppNL−G−F mice aged 8–9 months. Treatment reduced brain MAC and amyloid deposition, increased synapse density and improved cognitive performance compared to isotype control-treated AppNL−G−F mice. The findings implicate MAC as a driver of pathology and highlight the potential for complement inhibition at the level of MAC as a therapy in Alzheimer’s disease

Absence of CD59 in guinea pigs: Analysis of the Cavia porcellus genome suggests the evolution of a CD59 pseudogene

CD59 is a membrane-bound regulatory protein that inhibits the assembly of the terminal membrane attack complex (C5b-9) of complement. From its original discovery in humans almost 30 years ago, CD59 has been characterized in a variety of species, from primates to early vertebrates, such as teleost fish. CD59 is ubiquitous in mammals; however, we have described circumstantial evidence suggesting that guinea pigs (Cavia porcellus) lack CD59, at least on erythrocytes. In this study, we have used a combination of phylogenetic analyses with syntenic alignment of mammalian CD59 genes to identify the only span of genomic DNA in C. porcellus that is homologous to a portion of mammalian CD59 and show that this segment of DNA is not transcribed. We describe a pseudogene sharing homology to exons 2 through 5 of human CD59 present in the C. porcellus genome. This pseudogene was flanked by C. porcellus homologs of two genes, FBXO3 and ORF91, a relationship and orientation that were consistent with other known mammalian CD59 genes. Analysis using RNA sequencing confirmed that this segment of chromosomal DNA was not transcribed. We conclude that guinea pigs lack an intact gene encoding CD59; to our knowledge, this is the first report of a mammalian species that does not express a functional CD59. The pseudogene we describe is likely the product of a genomic deletion event during its evolutionary divergence from other members of the rodent order

Compendium of current complement therapeutics

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 many diseases, in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The driving role of complement in a single disease, paroxysmal nocturnal hemoglobinuria (PNH), provoked the development and eventual FDA (US Food and Drug Administration) approval of eculizumab (Soliris™), an anti-C5 antibody, for therapy. Although PNH is very rare, eculizumab provided clinical validation and demonstrated that inhibiting the complement system was not only well-tolerated, but also provided rapid therapy and saved lives. This clinical validation, together with advances in genetic analyses that demonstrated strong associations between complement and common diseases, drove new drug discovery programmes in both academic laboratories and large pharmaceutical companies. Numerous drugs have entered clinical development and several are in phase 3 trials; however, many have fallen by the wayside. Despite this high attrition rate, crucial lessons have been learnt and hurdles to development have become clear. These insights have driven development of next generation anti-complement drugs designed to avoid pitfalls and facilitate patient access. In this article, we do not set out to provide a text-heavy review of complement therapeutics but instead will simply highlight the targets, modalities and current status of the plethora of drugs approved or in clinical development. With such a fast-moving drug development landscape, such a compendium will inevitably become out-dated; however, we provide a snapshot of the current field and illustrate the increased choice that clinicians might enjoy in the future in selecting the best drug for their application, decisions based not only on efficacy but also cost, mechanistic target, modality and route of delivery