The role of B cell regulation in type 1 diabetes in NOD mice

Type 1 diabetes (T1D) is caused by an immune attack on the insulin producing beta cells of the pancreas. It often starts in childhood and T1D affects about 10% of all people who have diabetes. It is increasing in the population. and the greatest increase is occurring in children less than 5 years of age. There is an urgent need to understand why the immune system attacks the beta cells in order to develop treatments that will delay complete loss of the beta cells, and in the future to prevent disease. Currently there is no cure for diabetes and patients need lifelong insulin injections to maintain health. However, in spite of this, a significant proportion will develop long term complications affecting the eyes, kidneys, nerves and small and large blood vessels with the problems that accompany these.
A number of different white blood cells are involved in this attack on the insulin producing cells leading to diabetes. White blood cells called B cells produce antibodies which are very important markers of the immune attack on insulin-producing beta cells. Insulin is a major target of these B cells and antibodies to insulin are often found in children who develop diabetes. New therapies that remove B cells for a period of time are in trial to try to protect beta cells and the drugs are effective for a short period of time but then lose their effect. It important to understand why this occurs in order to improve on the treatment.
Normally B cells have many functions. Some are vital for protection against infection, but others may also help turn off immune responses when no longer needed. We will study whether these protective B cells are defective in diabetes. Our research will use the Non obese diabetic (NOD) mouse model of type 1 diabetes, which develops diabetes that is similar to the human disease and the mice can be treated in a similar way to humans to remove the B cells and prevent diabetes. In these NOD mice, we will test if the B cells that are normally protective and can dampen other immune responses lose the ability to protect when the mice get older and develop diabetes. We will study the effect of removing B cells that recognise insulin. Our project will also test how the B cells communicate with cells that can damage the pancreas, and this research will give us new tools to understand how well treatments that remove B cells work, and potentially to help design improved treatments. Our overall aim is to understand how regulatory B cells can be used to protect against T1D.

In type 1 diabetes, pathogenic T cells destroy insulin-producing beta cells. Although autoantibodies are present in humans to a number of autoantigens, antibodies to insulin, indicating the presence of insulin-reactive B cells, are often present early and are more likely to be found in young children who develop the disease. The Non-obese diabetic (NOD) mouse develops spontaneous diabetes that has considerable similarities to the human disease and both T and B cells are important in pathogenesis of the diabetes. Although T cells are directly pathogenic to the islet beta cells, recently, anti-CD20 monoclonal antibody therapy has been shown to delay progression of disease in patients who are newly diagnosed with diabetes. This is one of the few immunotherapeutic strategies that has shown promise. In NOD mice, several strategies to deplete B cells, including the use of anti-CD20, have also delayed and prevented the onset of diabetes. Importantly normoglycemia was restored in a proportion of mice after the onset of diabetes. We have previously shown that B cells that repopulate after depletion treatment have an increased percentage of a "regulatory" phenotype. In this project, we will investigate whether regulatory B cell function is defective in the NOD mouse model, particularly as the mice age and develop diabetes. Although there are a number of targets of the autoimmune attack, insulin is considered to be a primary autoantigen. We will use transgenic models to specifically study the effect of B cell depletion on insulin-specific B cells. Our studies will test whether removal of insulin-specific cells leads to protection or if insulin-specific B cells repopulate with a regulatory phenotype and it is these regulatory B cells that are protective. Our studies will also focus on the interaction of insulin-specific B cells with pathogenic insulin-specific T cells and examine whether this interaction can be exploited to protect against diabetes.

The academic beneficiaries include researchers engaged in both diabetes and immunological research as described above.
Ultimately the aim is to benefit patients who develop T1D or who are at risk of developing the disease in identifying targets which could be used to develop treatment and prevention. As T1D is a chronic disease, that starts early in life, and which leads to considerable morbidity and early mortality in a proportion of patients, it is vital to develop new treatments that could improve the longevity of the insulin-producing cells. This is because it is much easier to control blood sugar, even with a small amount of residual beta cell function. Understanding the process that could boost immune regulation, in order to build on a partial therapeutic success thus far, would be very important for patients with diabetes and will help to delay, or prevent diabetes complications. This would be of significant importance as currently diabetes complications are a major cause of morbidity and mortality. Retinopathy affecting the eyes is the leading cause of blindness in young people, nephropathy affecting the kidneys is the leading cause of renal failure, and accelerated atherosclerosis affecting large blood vessels can cause sudden premature death from myocardial infarction. If successful, the patients who will develop the disease and for whom immunotherapy would be a treatment to delay beta cell loss would be major beneficiaries. It could also have impact on individuals who receive pancreas or islet cell transplants in facilitating development of improved treatment that may protect and prolong graft function. In the future, it is hoped that it will be possible to use immunotherapeutic strategies to prevent diabetes.

In terms of a greater understanding of the current limitations of anti- B cell therapy, commercial enterprises that are interested in developing immunotherapy for type 1 diabetes could be beneficiaries of this work.
In addition, the results of this work will be of importance to the charities who support diabetes research and patient groups, both nationally and internationally, to allow them to communicate increased understanding of disease and to demonstrate how basic knowledge of scientific processes may allow therapies to be developed and improved.

Current efforts devoted to immunotherapy to treat type 1 diabetes to offer a delay in beta cell loss have not yielded many promising candidates. However, B cell depletion is one of the few where there may be continued hope. Increasing understanding of the effects of this treatment may lead to improved strategies to improve the efficacy. Thus, the proposal has the potential for commercial application within three to five years if successful.