Periodic Reporting for period 1 - DevoSignGammaDelta (Tracking γδ T cell development and TCRγδ proximal signalling)
Reporting period: 2018-09-01 to 2020-08-31
T cells and B cells, the two main components of adaptive immunity, express highly diverse antigen receptors generated by somatic gene rearrangement during their development. T cell development is restricted to the specialized environment of the thymus. Two types of T cells are conserved throughout evolution and across species: alphabeta and gammadelta T cells. In the thymus, alphabeta T cells develop through discrete steps from co-receptor CD4-CD8- (double negative, DN) T-cell receptor (TCR)- via CD4+CD8+ thymocytes into mature CD4+ or CD8+ single positive TCRalphabeta+ T cells, which populate the peripheral lymphoid tissues and are restricted to recognize antigens as peptides bound to major histocompartibility complex (pMHC). gammadelta T cells develop in the thymus alongside alphabeta T cells, but rearrange a distinct TCR (TCRgammadelta) that is not restricted by classical MHC. Successive waves of gammadelta T cells develop in the fetal and later in the adult thymus and different waves are associated with variable TCR-Vgamma segment usage, functional differentiation and localization in different tissues. Unique antigen-specificities of gammadelta T cells, their high clonal frequency and pre-activated differentiation status allows for their rapid, innate-like responses and confers them non-redundant roles in immune responses to infections and tumours.
Why is it important for society?
gammadelta T cells can effectively kill tumour cells and provide IFNgamma-mediated protective responses against cancer. Still, in some cases they can promote tumour growth via IL-17A production. Together with the recent advancements in T cell-based immunotherapy for cancer, gammadelta T cells are becoming an attractive tool for clinical treatments. Still, our knowledge of gammadelta T cells biology and development is rather limited and requires investigation to improve fine-tuning and manipulation for their clinical use.
What are the overall objectives?
This research project aims to elucidate the developmental trajectories and requirements of different gammadelta T cell subsets. To this end, we investigate i) the lineage relationship from uncommitted thymic progenitor cells to mature gammadelta T cell effector subsets producing either IL-17 (named gd17) or IFNgamma (named gdIFN), ii) the impact of TCRgammadelta signalling during thymic development and iii) the role of on candidate genes differentially expressed between gd17 and gdIFN cells and their role in gammadelta T cell subsets development.
We established a protocol to stimulate immature CD24+ gammadelta T cells from fetal thymi in vitro to measure consequences of TCR activation. These studies demonstrated that forced TCR ligation of fetal gammadelta T cells induced reduction of mitochondrial membrane potential and a metabolic shift from oxidative phosphorylation (in the unstimulated gammadelta progenitors) to aerobic glycolysis in gammadelta thymocytes that commit to the gdIFN pathway. This suggested that the different metabolic profiles associated with the gd17 and gdIFN phenotypes are already established in the thymus most probably following TCR-mediated “selection” (Lopes et al., Nature Immunology in press).
We hypothesised that TCR signalling might qualitatively differ between gd17 and gdIFN cells. To identify candidate genes differentially expressed in the two gammadelta T cells effector subsets, we compared the transcript levels of signalling mediators and transcription factors downstream of TCR and cytokine receptors in gd17 and gdIFN subsets using transcriptome data. The identified candidate genes were further investigated for their roles in the development of gammadelta T cells. Using different loss- and gain-of-function approaches in vitro and in vivo, we further analysed the impact of selected candidate genes on i) T cell development, ii) gd17 and gdIFN commitment and iii) cytokine production.
By tracking subpopulations of gammadelta thymocytes throughout ontogeny (from fetal to adult development), we identified a novel gammadelta T cell population that produces IFNgamma but not IL-17 and develops mainly in the perinatal period. These enigmatic gdIFN cells were further investigated during the course of the action. We characterized their developmental requirements and kinetics, established them as a stable perinatal gammadelta T cell subset and a preferential target in the development of leukemia. Given the functional and ontogenic characteristics of this novel gdIFN subset, we anticipate it may play important roles in anti-viral or anti-parasitic defense in early life.
We will explore the possibilities to translate these novel findings from the murine to the human immune system with the ultimate goal to test its potential for immunotherapy.