Understanding thymic acquisition of gamma/delta T cell effector function

Gamma/delta T cells make non-redundant immune responses to infections such as HIV, influenza, tuberculosis and malaria, and have critical roles in immunopathologies such as psoriasis and multiple sclerosis. Moreover, gamma/delta T cells are now considered attractive candidates for immunotherapy strategies against cancer. Indeed, a recent study of 18,000 cancer patients with 39 different malignancies revealed a tumour-associated gamma/delta T cell expression profile as the single biggest positive prognostic immune-related indicator.

Gamma/delta T cells administer their tissue-associated effector functions largely through early provision of cytokines and chemokines that influence both the local tissue environment and downstream alpha/beta T cell-mediated adaptive immune responses. Secretion of interferon gamma (IFN-gamma) and interleukin-17A (IL-17A) are central components to this effector function; for example, IFN-gamma is implicated in anti-viral and anti-tumour immune responses, while IL-17A is critical for clearance of fungal infections.

Despite being superficially similar (e.g. expressing a T cell receptor) to alpha/beta T cells, gamma/delta T cells are now recognised as having important differences. Unlike alpha/beta T cells that only commit to specific effector functions during an immune response, gamma/delta T cells acquire their effector function (i.e. to produce IFN-gamma or IL-17A) during development in the thymus. The mechanistic processes that drive this thymic commitment to effector fate are still being explored, but undoubtedly represent a key foundation stone for fully understanding gamma/delta T cell biology.

Our recent work on gamma/delta T cell development has led to the following hypotheses; that the gamma/delta T cell receptor (TCR) instructs gamma/delta progenitors to adopt specific fates during thymic development; that engagement of discrete signalling pathways downstream of the gamma/delta TCR drives differential commitment to distinct effector fates, and; that adoption of appropriate metabolic programs is crucial for thymic acquisition of gamma/delta T cell fate and subsequent effector function.

To test these hypotheses we will combine state-of-the-art techniques in vitro (e.g. thymus organ cultures, single-cell RNA analyses, retroviral gene transduction) with studies in gene-deficient mice in vivo. In major aim-1, we will assess characteristics of the gamma/delta TCR that drive commitment to distinct effector fates (e.g. importance of the TCR highly variable regions, the sub-type of TCR chain used, the timing of TCR expression, and dependence on binding to activating or inhibitory ligands). In major aim-2, we will examine the importance of discrete signalling networks to adoption of distinct effector fates (e.g. those controlled by PI3-kinase, ERK/MAPK or NF-kappa-B), with emphasis on how these interact with transcription factor networks. Finally, in aim-3 we will assess the mechanisms that regulate the differential metabolic programming of developing gamma/delta T cells and how this impacts on subsequent gamma/delta T cell function.

The studies detailed in this proposal will significantly advance the field of gamma/delta T cell biology. Gamma/delta T cells are increasingly considered to connect the broadly reactive, rapidly acting innate immune system with the delayed responses of the pathogen-specific adaptive immune system. Thus, understanding how features of adaptive immunity (e.g. TCR expression/signalling) instruct acquisition of innate-like qualities (e.g. rapid secretion of cytokines) will be particularly illuminating. Moreover, understanding gamma/delta T cell development will provide critical insight into gamma/delta T cell function. In turn, this will better inform augmentation of gamma/delta T cell responses in disease, and will better advise how these cells can be utilized in immunotherapeutic approaches, for example in anti-tumour strategies.

Gamma/delta T cells make non-redundant immune responses to infections such as HIV, tuberculosis and malaria, and have critical roles in immunopathologies such as psoriasis and multiple sclerosis. Moreover, gamma/delta T cells are now considered attractive candidates for immunotherapeutic strategies against cancer. Gamma/delta T cells execute their tissue-associated effector functions largely through early provision of cytokines, primarily interferon-gamma and interleukin-17A. However, unlike alpha/beta T cells that commit to effector function during an immune response, gamma/delta T cells acquire their effector potential during development in the thymus. The mechanistic processes that drive this are presently unclear, but represent a key foundation for fully understanding gamma/delta T cell biology.

This proposal will use state-of-the-art techniques in vitro (e.g. thymus organ cultures, single-cell RNA analyses, retroviral gene transduction) combined with studies in gene-deficient mice in vivo, to test the following hypotheses; that differential thymic commitment to distinct gamma/delta T cell effector fates is driven by; (i) physical characteristics of the gamma/delta T cell receptor (TCR); (ii) discrete signalling networks (e.g. PI3-kinase, ERK/MAPK or NF-kappa-B pathways), and; (iii) adoption and maintenance of specific metabolic programs. The studies detailed here should significantly advance the field of gamma/delta T cell biology. For example, an understanding of how features of adaptive immunity (e.g. TCR expression) instruct acquisition of innate-like qualities (e.g. rapid secretion of cytokines) will be particularly illuminating. Moreover, understanding development provides critical insight of function, that will better inform augmentation (or inhibition) of gamma/delta T cell responses in disease, and will better advise how these cells can be utilized in immunotherapeutic approaches, for example in anti-tumour strategies.

Queen Mary University of London, Barts and the London Medical School, The Blizard Institute within the Medical School, and the Centre for Immunobiology, as well as the applicant, are fully committed to the concept of maximizing the impact of research through communication and collaboration with industry, the public sector, and other third party organizations. Specific examples are as follows:

Applicant: The applicant will disseminate all findings from the current proposal at relevant congresses (e.g. British Society for Immunology, Biennial International gamma/delta T cell congress etc). The applicant will also target high impact journals for publication of findings, and ensure that all publications comply with open access regulations. The applicant is presently collaborating with two biotech partners; hVIVO (London http://hvivo.com - located within the Innovation Centre on the Medical School campus) on T cell responses to infectious disease, and Immunocore (Oxford - http://www.immunocore.com) on developing T cell receptor-based therapies. Both collaborations utilize findings from the basic research program of the applicant's lab (that is continued in the present proposal). The applicant is also a member of the Medical School's Centre for inflammation and therapeutic innovation (CiTI - http://www.qmul.ac.uk/citi/partners/ - see below), and is the Lead for the Centre for Immunobiology interface with the Medical School's East London Genes and Health initiative (ELGH - http://www.genesandhealth.org - see below). The applicant also leads a Centre for Immunobiology initiative to have regular joint research meetings with infectious disease clinicians from Barts NHS Trust to identify areas of overlap and collaboration that links basic and applied research. Thus, there is ongoing and active engagement with partner colleagues/organizations (industry, NHS, local community) to maximize the application/translation of research in the applicant's lab and Centre wherever possible.

Medical School: Barts and The London Medical School runs several initiatives that seek to interact with both industry and society to communicate and disseminate the outcomes and advances of research within its Institutes. The ELGH initiative seeks to sequence the exomes of 100,000 volunteers from the local Bangladeshi and Pakistani communities to identify homozygous loss-of-function mutations that adversely affect the health of these individuals. The applicant leads the immunology interface with this program that seeks to translate findings from basic immunology research in the Centre for Immunobiology into a human setting. This immunology initiative is actively seeking collaborators from other UK (and some overseas) institutions to further the progress of understanding in human immunology. The applicant is also a member of the Medical School's CiTI initiative. This unites inflammation/immunology-related research groups across the Medical School to actively seek collaborative opportunities with biotech and pharma companies (e.g. with UCB, Pfizer etc).

QMUL: The University is a member of UCLPartners (https://uclpartners.com/who-we-are/) that fosters collaboration between more than 40 partners from the NHS, social care and academia, to drive discovery science, innovation into practice, and population health. The applicant is an active member of UCLPartners' Infection, Immunology and Inflammation (III) initiative.

Public engagement: The Blizard Institute houses a Bioscience Education Centre, the "Centre of the Cell", which aims to engage young people and schools in the principles of scientific and biomedical research. The Centre of the Cell opened in September 2009 and approximately 10,000 children (age 9 to 17) visit each year. The applicant actively engages with this initiative, regularly speaking with students about work conducted in his lab. The applicant also takes approx. 10 work experience students (age 16-17) each year.