Investigating the role of gamma delta (γδ) T cells in the control of Mycobacterium tuberculosis infection

SUMMARY Mycobacterium tuberculosis (Mtb) is the pathogenic bacteria which causes tuberculosis (TB) disease and was responsible for 1.6 million deaths worldwide in 2021. It is well-established through human and animal studies that alpha-beta (αβ) T cells are important for the control of Mtb infection, but the role of gamma-delta (γδ) T cells is less well-defined. γδ T cells express T cell receptor (TCR) heterodimers comprised of a γ-chain and δ-chain that mediate recognition of a variety of lipids or small molecules presented by major histocompatibility-like ligands, such as cluster of differentiation 1 (CD1) or butyrophilin molecules. There is growing evidence that γδ T cells are important in the early protective immune response against Mtb in the lung. The central hypothesis of this application is that γδ T cells contribute to control of Mtb infection through recognition of mycobacterial lipids and promotion of an enhanced adaptive immune response. A subset of γδ T cells, termed Vδ1 cells, are enriched in tissue and have known reactivity to mycobacterial lipids presented by CD1 molecules. In AIM 1 we will evaluate the molecular mechanisms underlying Vδ1 T cell lipid antigen recognition through analysis of in vitro expanded clones and computational analysis of lipid-specific Vδ1 TCR motifs. By investigating specific TCR motifs governing recognition of mycobacterial lipids by Vδ1 T cells, we will determine shared TCR characteristics that will enable their identification in clinical cohorts. A major challenge to the field has been the lack of a suitable animal model to understand the role of γδ T cells in mediating protective immunity to Mtb. We will develop a novel in vitro granuloma model using the palatine tonsil, a readily accessible human mucosal tissue, and investigate the role of γδ T cells in mechanisms of bacterial control. Our preliminary data reveal that the tonsil contains γδ T cell subsets which respond to in vitro mycobacterial infection and specialized dendritic cells subsets that can prime T cell responses. Thus, in AIM 2 we will use tonsil cells to study γδ T cell interactions with dendritic cells in response to mycobacterial infection and develop an in vitro granuloma model and investigate the role of γδ T cells in granuloma organization. A tractable tonsil-based in vitro granuloma system will be an important contribution to the field and provides a unique system to interrogate the function of γδ T cells in response to Mtb. Together, our proposal will lead to increased understanding of γδ T cells and profile their involvement in the protective immune response to mycobacteria.