Periodic Reporting for period 4 - Tissue-Tregs (Novel approaches to determining the function of tissue-specific regulatory T cells) Reporting period: 2020-07-01 to 2021-11-30 Summary of the context and overall objectives of the project Regulatory T cells (Tregs) are formed through the expression of the transcription factor Foxp3 in T cells, resulting in the rewiring of the cell function into an immunosuppressive phenotype. Recently, it has been proposed that Tregs also have additional tissue-specific physiological roles when resident in different tissues. For example, tissue-specific Tregs residing in the muscle and adipose tissue possess immunological and non-immunological functions in these tissues, distinct from the generic Tregs in circulation. Currently, research into tissue-specific functions of Tregs, or any other migratory cell type, is limited by the available research tools. This project generated new synthetic biology tools for enriching tissue-resident cells and then applied these tools to the study of tissue-resident Tregs in the brain, lung, liver, kidney and pancreas, thus creating a comprehensive atlas of tissue-specific functions. We developed a new system for gene delivery of a Treg-specific survival factor in a tissue-specific manner, allowing this directed expansion and functional testing. We found a key role of brain-resident Tregs in preventing and repairing neurological damage. These studies were extended by systematic molecular, cellular and kinetic analysis using existing innovative methods established in the laboratory. Our tissue-specific gene delivery system will have a profound impact on immunology beyond the direct scope of the project, by providing a proof-of-principle approach for study tissue-specific immunology. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far TISSUE-TREG was based on characterising Treg in the tissue, and using novel synthetic biology circuits to expand these populations in different tissues. The project required substantial development of synthetic biology circuits which needed to be designed, tested and validated in vitro and then new mice generated before testing in vivo. The project saw substantial progress in characterising the biology of tissue Tregs across various tissues, in particular the brain. The work has found that tissue Tregs gain their profile and function in situ following several weeks of residency in the tissue, and migrate out of the tissue again after several months. The profile of a tissue Treg appears to be relatively independent of the tissue in which it resides, demonstrating a conserved pan-tissue function. Work on expanding the tissue Treg populations allowed a direct demonstration of the functional role of brain-resident Tregs in preventing and repairing neurological damage. Key outputs from this work include Pasciuto et al Cell, 2020; Roca et al, Nature Communications, 2021 and Yshii et al, Nature Immunology, in press. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The development of a method to expand up tissue Tregs is beyond state of the art. It is the first time that a multi-cellular synthetic circuit has been used in vivo to couple the behaviour of a migratory cell to its anatomical location. The system provides a proof of principle method to assess the cellular function of migratory immune cells in a tissue-specific manner. This system was patented as PCT/GB2020/052148, with ongoing efforts to commercialise the advance. Description of work
