Understanding the autoimmune mechanism in idiopathic membranous nephropathy (IMN)

Membranous nephropathy affects about 1200 adults in UK, mainly in middle age, with approximately 100 new cases diagnosed each year. Inflammation in the kidney damages the complex filtering unit so that large amounts of serum proteins are lost into the urine, The consequences can be serious when this state continues over time, increasing the risk of stroke, heart disease and infection. At least a third of patients will progress to chronic kidney disease stage 5 and require dialysis to survive. Treatment with potent drugs can be effective in up to 50% of patients and induce remission of disease but the treatments come with added risks of causing cancer later in life and increasing the existing cardiovascular risk. Interestingly, up to a third of patients can get better without immunosuppressive drugs. There has been a lot of debate by doctors about whom to treat, with what drug dose and duration but there is no consensus on the optimum treatment. The reason for lack of progress in treatment over the last 50 years is due to our lack of understanding of the disease mechanism. With no valid biomarker of the disease mechanism to use to monitor the effectiveness of treatments, clinicians have had to rely on non specific, wide ranging immunosuppressive drugs and simplistic protocols.
We recently reported the results of a large european collaborative study into the genetics of membranous nephropathy involving 556 patients. We identified two genes, DQA1 and PLA2R, that account for the risk of getting primary MN. Two years ago, another research group in USA identified an autoantibody to PLA2R in 70% of MN patients. We have already established the first quantitative immunoassay for this anti-PLA2R autoantibody and measured levels in patients in our european study. This breakthrough in new knowledge suggests that the disease is an autoimmune disease caused by anti-PLA2R, reacting with PLA2R on the podocyte in the kidney filter. Important questions to answer now are
a) how do these two genes interact to produce the anti-PLA2R autoantibody response?
b) can we identify the parts of the gene products that initiate the anti-PLA2R response?
c) can we use these sequences to regulate the immune system and thereby develop a novel and specific treatment
d) can we identify other genetic influences that promote anti-PLA2R production and disease progression on the one hand or that switch off antibody production on the other. These questions are the focus of our grant application.
We think the most informative strategy is to focus on understanding key aspects of the clinical disease. Firstly, we will study the immunogenetics of those patients with anti-PLA2R who progress to kidney failure compared to those who experience a spontaneous remission. This will inform us of the genetic signature that predicts severe disease outcome which could be useful to clinicians when considering whether or not to treat patients.
Secondly, we will study all patients who have had MN and been transplanted. Up to 50% of these transplants will suffer recurrence of the disease confirmed by biopsy and detection of the autoantibody. By studying the changes in DQA1 and PLA2R genetics that occur at transplantation between the donor-recipient pairs that have recurrent disease compared to the donor pairs where disease does not recur, we will be able to identify the pathogenic combinations that reactivate the disease.
This research will deliver predictive biomarkers of disease severity and outcome which will guide options for therapy. More importantly, knowledge of the mechanism will enable design of novel therapies to switch off autoantibody production to cure the disease.

The objectives are
1) to understand how DQA1 and PLA2R genes control quantity and specificity of anti-PLA2R production in IMN patients to induce proteinuria
2) to identify specific peptides in the target antigen that define B cell and T cell epitopes
3) to identify additional genetic factors that promote and maintain anti-PLA2R levels to cause disease progression
4) to characterise the natural immune regulatory control mechanism that switches off anti-PLA2R production and induces spontaneous remission
We already have GWAS SNP data and anti-PLA2R levels on 556 patients with IMN and will obtain clinical outcome data on these patients. In addition, we will sequence DNA on 200 cases of PLA2R positive MN who have progressed to CKD5 and who have been transplanted (samples collected through collaboration with UK Transplant Labs) This will enable us to test for genetic markers associated with high and low anti-PLA2R production and genes that predict disease progression.
We will sequence DQA1 and PLA2R genes in the donor for each donor recipient pair so that we know the genetic changes that occur at transplantation. Through classification of the transplant outcome at 5 years (proteinuria, anti-PLA2R status and/or biopsy) we can define recurrent and non-recurrent disease. In this natural experiment of genetic change we will test the validity of our genetic markers for high antibody production as predictors of disease and anti-PLA2R post transplantation.
We have identified a strategy of trypsin digestion of recombinant PLA2R and western blotting of fragments followed by mass spectrometry analysis to identify B cell epitopes. Bioinformatics predicts PLA2R peptide sequences binding to pathogenic DQA1 alleles

This research project will impact four major beneficiaries, i) pharmaceutical industry, ii) universities, iii) healthcare providers (NHS) and iv) patients
i) Pharmaceutical companies: Most autoimmune diseases have been treated empirically with non specific powerful immunosuppressive drugs e.g. steroids, alkylating agents that are off patent. This situation provides no incentive to engage companies to research new therapies. In the last 5 years, industry has developed biological agents targeting B cells (anti-CD20. anti-BLYS) to reduce antibody production in autoimmune diseases and these show promise from initial clinical trials in SLE and ANCA vasculitis. What is delaying their wider application to diseases such as IMN is the lack of suitable surrogate markers of disease activity in IMN, methods to identify suitable patients who might best benefit from such treatment and reliable outcome measures. Our new knowledge of the genetics controlling anti-PLA2R production and the genetics of progression/spontaneous remission will identify whom to treat. Knowledge of the immune regulatory mechanism will identify patients who are likely to experience spontaneous remission and unlikely benefit from treatment. Characterisation of the antibody titre, specificity and avidity over time will show whether treatment is being effective, what dosing is appropriate and when to stop treatment. This information will be invaluable to the pharmaceutical industry in helping to design effective clinical trials of anti-B cell therapies in IMN over the next 3-5 years.
ii) Universities: This consortium brings together 4 of the top UK research universities to promote research in IMN. No individual centre has the necessary expertise to progress this area, but together the research group is highly competitive at international level. The group will bring benefit to these UK Universities by winning major research contracts to develop this field particularly from EU FP7/8 over the next 5 years. Furthermore, there is significant intellectual property (IP) to be protected in this area for UK universities/spin out companies. This IP resides in knowledge of the precise B cell and T cell epitopes and how to use this knowledge to develop new diagnostic assays and novel therapeutic reagents. We expect the IP to be licenced in the first instance to UK Biotech to foster a programme of diagnostic/therapeutic development.
iii) Healthcare providers (NHS). As a result of this research, clinicians will be better able to manage IMN effectively. Renal biopsy is not always possible or desirable for some patients and cannot be used to monitor disease activity. The information we develop on the antibody titre, specificty, avidity will improve diagnosis in a cost effective way. Clinicians have long debated how to best select IMN patients for treatment as the available therapies have power to do significant harm. The information from our genetic studies will help target treatment to those patients who will benefit and also reduce waste of expensive drugs on patients unlikely to benefit. An immediate outcome of our genetic studies on recurrent disease will inform best practice regarding organ matching for kidney transplants where the recipient had IMN as their primary cause of renal failure. By proving our hypotheses, retaining the DR match for IMN patients may need to be changed and we will have the evidence base to convince the relevant authority (NHS Blood and Transplant) to trial a new approach to organ matching for these patients.
iv) Patients: The impact on patients is likely to be immediate and significant. Even existing therapies will be better targeted and monitored and patients will be put at less risk of comorbidity. More importantly, patients will be assigned treatment most likely to be effective for them based on their genetic parameters. If we can understand the problem of recurrent disease, precious organs will be better allocated to reduce early loss.