IMPC - Exploration of the potential of C7 blockade as a target for immune therapy in complement mediated kidney disease

Lead Research Organisation: Newcastle University
Department Name: Institute of Cellular Medicine

Abstract

Atypical haemolytic uraemic syndrome (aHUS) is a kidney disorder which without treatment rapidly progresses to kidney failure.

In work instigated in Newcastle, aHUS was linked to mutations in genes that are members of the complement system. Complement is part of our immune system and is designed to label and destroy bacteria/pathogens. Extensive laboratory and comparative model based analysis of mutations in complement factor H have established their direct role in many cases of aHUS. Factor H regulates C3 activation and C3 activation is central to full activation of complement. Loss of factor H function leads to over active complement and aHUS. Subsequently, we identified gain-of-function (GOF) mutations in C3 that associated with aHUS. To continue our analysis, we generated several unique recombinant mouse C3 molecules based on these mutations and transferred C3 hyperactivity to mouse C3. We then successfully generated a sophisticated mouse model based on one of the C3 mutations, a C3 GOF mouse model.

Our analysis suggests that this new mouse model is highly similar to aHUS in man and therefore offers a perfect test bed to develop and test new anti-complement therapeutics.

We at the National Renal Complement Therapeutic Centre (NRCTC) recognise that eculizumab (a drug that blocks the ability of complement to destroy cells) is a highly effective treatment in many patients with aHUS (greater than 80%). Eculizumab targets the function of the terminal pathway of complement and a mouse version of eculizumab has been found to protect the C3 GOF mice from disease. However, eculizumab is not a perfect drug, it is expensive and the effects of long term use are not yet fully known, it can also be made ineffective due to the quick turn over and variable expression of its target protein (C5). Finally, it's use also makes patients susceptible to infection by certain bacteria.

Because of the potential problems with eculizumab, many drugs are being developed but none so far have undergone successful clinical trails in these diseases. Complement component C7 is an another key member of the terminal pathway of complement and is almost unique in the terminal pathway in that it does not get significantly up regulated during infection, it is stable and expressed at relatively low levels making it a good target to for an anti-complement therapeutic. Here, we will establish whether removal of C7 protects C3 GOF mice from aHUS. We will also use the C7 deficient mice to develop anti-C7 monoclonal antibodies to investigate the ability of these reagents to reverse disease in the C3 GOF mice.

Our output will be a much clearer understanding of the role of the terminal pathway of complement in the rare kidney disease aHUS. We will also generate many new terminal pathway reagents including functionally blocking monoclonal antibodies. The project will provide detailed data regarding the efficacy of C7 blocking antibodies as an anti-complement therapy in this model, and whether this new complement therapeutic can provide better protection from this type of kidney disease in the future, compared to C5 blockade.

Finally, as activation of the complement system is involved in most, if not all, inflammatory conditions (such as age-related macular degeneration and control of cancer) and is linked to many autoimmune diseases (such as rheumatoid arthritis and lupus) this comparative model and the anti-C7 drug it may help validate, could eventually lead to the treatment of a wide range of inflammatory diseases/conditions.

Technical Summary

C3 is the central protein of the complement proteolytic cascade. We have generated a sophisticated floxed knock in mouse which carries a single-point mutation, p.Asp1115Asn (Met1) in C3 (C3-D1115N); this gain-of-function change in man results aHUS. Homozygous C3-D1115N mice develop severe kidney disease by P21 with all the hallmarks of a thrombotic microangiopathy disease mediated by over active complement, i.e. aHUS. We have shown that use of a monoclonal antibody to C5 in the C3-D1115N reverses the disease in the mice, in a manner analogous to eculizumab in man. We now wish to establish if the role of membrane attack complex is the critical factor in the development of aHUS and test whether targeting C7 will be sufficient to block disease. To achieve this, we will:
1. Establish if disease is present in homozygous C3-D1115N mice after backcross onto C7-/- deficient animals; using histological and biochemical analysis.
2. Use the C7 deficient mice to develop highly specific antibodies that will ideally block the function of both human and mouse C7; tested in both classical and alternative pathway based haemolytic assays.


This study will pave the way to potential new drugs for the treatment of complement mediated diseases. It will give concrete data on whether an intact membrane attack complex is necessary and sufficient to precipitate aHUS. These studies will be of immediate interest to industry and the ongoing efforts to generate drugs to replace eculizumab.

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