Identifying a crucial pathway by which regulatory T-cells control immunity via integrin alphavbeta8 and TGF-beta.

Our immune system must respond to pathogens that enter the body to prevent harmful infection. A key immune cell type in fighting infections is the T-cell. However, in addition to their protective roles, T-cells can sometimes attack our own body, resulting in devastating inflammatory diseases such as inflammatory bowel disease and multiple sclerosis. Thus, an important area of medical research aims to determine how T-cells are normally prevented from causing inflammatory disease, and what goes wrong to cause disease.

Recent studies have identified a crucial cell type in preventing harmful T-cell responses in the body. Thus, so-called regulatory T-cells (which express a particular protein molecule called Foxp3)
are a specialised type of T-cell which dampen harmful immune responses. Indeed, in both animals and humans who have mutations resulting in a lack of regulatory T-cells, severe inflammatory disease occurs. Based on promising results in animal models, there is great interest in the potential use of regulatory T-cells as a therapy for human inflammatory disease (by injecting patients with regulatory T-cells to inhibit harmful T-cell responses). It is therefore extremely important to understand the ways in which regulatory T-cells suppress harmful immune responses, so we can use this information to design better regulatory T-cell-based therapies for inflammatory disease.

Our new recent work has identified a novel, important pathway by which regulatory T-cells suppress harmful T-cell responses. Previous work has indicated that a protein called TGF-beta plays an important role in the biology of regulatory T-cells. Many cells can make TGF-beta, but it is always made as an inactive complex which needs to be activated to function. We have now found that regulatory T-cells are capable of activating TGF-beta, and that this activation requires the regulatory T-cell to express a specific protein called integrin alphav beta8. Importantly, using an animal model of inflammatory bowel disease, we find that regulatory T-cells that do not express integrin alphav beta8 can no longer suppress T-cell-induced inflammation. Thus, this novel integrin alphav beta8-TGF-beta pathway on regulatory T-cells appears crucial in their ability to control harmful T-cell responses.

However, there are still many important questions which we aim to address in this proposal, using a combination of mouse models and human tissue samples from patients with inflammatory disease. Thus, there are several different types of regulatory T-cell expressing Foxp3, and we will look to identify if a particular subset of these cells are better able to activate TGF-beta via integrin alphav beta8 and suppress T-cell responses. Additionally, we aim to determine in detail how TGF-beta activation by the integrin on regulatory T-cells promotes their ability to inhibit harmful T-cell responses. We will also study whether the pathway is important in other inflammatory diseases in addition to inflammatory bowel disease. Finally, we will discover whether the pathway is important in human inflammatory disease, using cells isolated from patient samples acquired from local hospitals.

Our work will therefore identify a crucial way in which regulatory T-cells prevent T-cell responses from causing inflammatory disease. Such information will be extremely useful in designing potential novel therapies, aimed at promoting the ability of regulatory T-cells to dampen harmful inflammation caused by T-cells.

T-cell-mediated immunity is essential in protection from pathogens, but aberrant responses can lead to inflammatory diseases such as inflammatory bowel disease and multiple sclerosis. Key cells in preventing harmful T-cell responses are CD4+ Foxp3+ regulatory T-cells (Tr). Mutations that prevent Tr development cause severe T-cell mediated inflammation in mice and humans, and transfer of Tr into mice protects from ongoing inflammation. Indeed, current human clinical trials are attempting to use Tr as a therapy in human inflammatory disorders. Thus, it is crucial that the mechanisms by which Tr control T-cell responses are determined, to aid development of future Tr-based therapies for inflammatory disease.

Our exciting preliminary data reveal a novel pathway by which Tr suppress inflammation. We find that Tr activate latent forms of the cytokine TGF-beta, via expression of the integrin alphav beta8 (avb8). Importantly, expression of integrin avb8 is essential for Tr to suppress inflammatory T-cells in a mouse model of colitis. Thus, our data suggest that TGF-beta activation by Tr, via a specific integrin, is fundamentally important in Tr-mediated control of inflammatory T-cell responses.

However, many important questions remain. Are specific Foxp3+ Tr subsets specialised to activate TGF-beta via integrin avb8, and what are the mechanisms by which avb8 supports Tr-mediated T-cell suppression? Is the pathway important in other inflammatory diseases, or is it specific for T-cell regulation in the gut? Is the pathway dysregulated in human inflammatory disease?

Using conditional KO mice, in vitro immune cell assays and human tissue samples, we will address these important questions, uncovering a central mechanism by which Tr regulate inflammatory T-cell responses via TGF-beta activation. Such work is crucial in identifying potential therapeutic targets for promotion of Tr function, with the aim of dampening T-cell responses in inflammatory disease.

Disorders of the immune system are a major health problem in the UK, placing an increasing burden on health care resources. In order to determine how our immune system maintains health and how dysregulation results in disease, it is essential that the underlying biological mechanisms that control immune responses are understood. Our project will have important impact in this area, by identifying and characterising crucial cellular and molecular mechanisms by which the immune system is regulated to prevent inflammatory disease. Specifically, we will identify a key novel pathway by which regulatory T-cells suppress T-cell responses, via activation of the multi-functional cytokine TGF-beta. The work will therefore be of potential benefit to a wide range of people.

Discoveries made during our proposal will be of interest and importance to the large field of clinical and non-clinical researchers who study the basic biology of immune regulation. Given the crucial importance of regulatory T-cells in preventing immune-mediated disease, and the broad role of TGF-beta in regulating many different aspects of immunity, our findings will inform the work of researchers from a diverse range of immunological backgrounds. Our proposal aims to define a central immunoregulatory pathway that controls T-cell responses in inflammatory bowel disease and multiple sclerosis. Thus, work will be important to researchers specifically interested in the pathology of such diseases in addition to those more interested in the general mechanisms by which the immune system is controlled.

Given the vital function of TGF-beta in the biology of non-immune cells, defining mechanisms that control TGF-beta activity will be pertinent to biologists interested in broader aspects of cell biology, ranging from researchers interested in the basics of cell behaviour (migration, differentiation, apoptosis) to researchers interested in the cell biology of diseases such as fibrosis and cancer (in which TGF-beta has been implicated to play important roles). Other researchers will therefore benefit from our work by providing novel insights to inform their own research questions and direction.

Additionally, given that the molecular pathway we intend to study controls activation of TGF-beta, a molecule that controls a wide range of cellular functions, our work is likely to be of much broader interest to the drug discovery industry. Indeed, TGF-beta is already a therapeutic target by a number of companies for treatment of several disorders. Hence, mechanistic insights into how this molecule is controlled is likely to be of potential benefit and interest to the drug discovery industry, by defining novel components of the TGF-beta pathway to target therapeutically. In the longer term, these benefits to industry will hopefully lead to benefits for the wider public, via the production of novel drugs to promote health.

In addition to potential benefits via the drug discovery industry, our proposal will aim to achieve greater immediate impact with the general public by using our research as a basis for a range of public engagement events. These events will benefit the public by increasing awareness of how the immune system works, the importance of immunity in the maintenance of health, and the ways scientists carry out basic research with a view to better understanding complex systems.

Our work will also benefit the research teams involved by establishing and strengthening research collaborations, allowing important technical expertise to be transferred between labs (e.g. EAE models from Anderton group in Edinburgh to Travis group in Manchester) and basic-clinical immunology links to be strengthened in Manchester. Additionally, the post-doctoral research associate (PDRA) Worthington will receive extensive training in new immunological in vivo models that will benefit his future career.