THE ROLE OF CD8:B-LYMPHOCYTE INTERACTIONS IN TYPE 1 DIABETES PATHOGENESIS

PhD student: Emily Hanton
Supervisor at TUD: Ezio Bonifacio
Supervisor at KCL: Timothy Tree, Mark Peakman
Start date: 01.10.2017  Date of defense: 24.05.2021 PhD

Class I major histocompatibility complex (MHC-I) molecules on antigen presenting cells (APCs) present peptides derived from extracellular proteins to CD8 T cells (termed cross-presentation) to induce or maintain antigen-specific cytotoxic effector responses. This interaction may be important in autoimmune disorders such as type 1 diabetes (T1D), since self-reactive CD8 cytotoxic T cells are direct mediators of pancreatic β-cell damage. Little is known of the key APCs governing self-reactive CD8 T cell responses in the islets, however. Since recent evidence has highlighted B cell involvement in insulitic lesions in T1D, this study set out to test the hypothesis that B cells cross-present exogenous polypeptide to CD8 T cells and thus influence CD8 T cell effector responses in a way that could be relevant to β-cell destruction. During the thesis, development of an antigen delivery system (ADS) to target a selected antigenic polypeptide for uptake via the B cell receptor (BCR) led to the demonstration that co-culture of ADS-pulsed B cells with cognate antigen-specific CD8 T cell clones induced marked CD8 T cell degranulation, a marker of effector function following T cell activation. As a benchmark of cross-presentation potency, immature monocyte-derived dendritic cells were matured in the presence of the same polypeptide and comparable levels of degranulation were observed. Within B cell: CD8 T cell clone co-cultures, CD20⁺ CD8⁺ doublets were identified, suggesting a sustained interaction between CD8 T cells and B cells. Doublets were also detectable in the absence of cognate polypeptide; however functional T cell output and formation of a mature immunological synapse was only observed in the presence of cognate polypeptide. To further investigate the nature of this interaction between CD8 T cells and B cells, receptor-ligand pair expression between the two cells was studied by transcriptomic analysis. This revealed potential cell-cell communication pathways of signalling and adhesive capabilities. Finally, to provide an opportunity for analysis of these interactions in a tissue context, single B cells were isolated from the pancreatic islets of a T1D patient by laser capture microdissection, and their molecular phenotype studied. Thus, this project provides a novel insight into the role of B: CD8 lymphocyte interactions in the tissue pathobiology of T1D. 

Publication:

GAD-alum immunotherapy in type 1 diabetes expands bifunctional Th1/Th2 autoreactive CD4 T cells. S. Arif, I. Gomez-Tourino, Y. Kamra, I. Pujol-Autonell, E. Hanton, T. Tree, D. Melandri, C. Hull, D.K. Wherrett, C. Beam, B.O. Roep, A. Lorenc, M. Peakman. Diabetologia. 2020;63:1186-1198.