Initiation of anti-islet autoimmunity: Regulation of MHC class II expression in the islet microenvironment

Type 1 diabetes (T1 D), a prototypic CD4 T cell mediated autoimmune disease, is believed to have a prolonged pre-clinical phase that lasts many years. Therapeutic intervention during that period of the disease has demonstrated effectiveness in a small subset of patients and for a limited time. Towards finding a cure, we have decided to investigate the very early phase of the disease in mice and human. Our focus has been closely linked to the genetics of the disease and its association to MHC class II genes and products. Because the evidence put CD4 T cells as initiators of the autoimmune process, defining the antigen presenting cells (APCs) that control pathogenesis is essential. We have recently described a non-hematopoietic CD45- cell associated to the efferent post-capillary collecting venule that expresses MHC-II and spontaneously presents islet antigens to CD4 T cells. Further characterization of this cell showed that it is fibroblastic and epithelioid in nature. More importantly, it coexpresses PD-L 1 with MHC-II but no coreceptors, and can anergize pre-activated T cells. We hypothesize that this cell protects islets from immune attacks but is overwhelmed by blood derived APCs when local inflammation persists and disease progresses. In Specific Aim 1, we will perform a time course characterization of CD45- and CD45+ APCs that are associated to the islets and control anti-[\-cell autoimmunity. This landscape of APCs will be defined in normal pancreatic islets, and islets of pre-diabetic mice. Traditional methods of immunocytochemistry and more sensitive methods of cell tracking will be used to characterize every MHC-II+ cell type associated with the normal pancreatic islet and the islet progressing towards autoimmunity. Transgenic mice expressing eGFP MHC-II, optimized high affinity anti-islet TCRs as well as spatial transcriptomics will be other tools used for this aim. In Specific Aim 2. we will further characterize the MHC-II+ PD-L 1+ tolerogenic fibroblast This aim will focus on: the nature and pathways of antigen presentation in those cells, their embryologic origin, the definition of their function at the initiation of T1 D, and their potential utilization for the prevention of T1 D? To overcome their very small numbers in the islet, mouse and human cell lines have been established. In addition, mouse to human translation will be facilitated by our ability to differentiate a similar cell from ES and iPSC cells. In Specific Aim 3. the regulation of MHC-II expression on non-hematopoietic cells associated with the islet, endothelial cells and fibroblasts, will be studied. In addition to IFNy, the main driver of MHC-II expression, new molecules such as a fragment of gasdermin D will be examined in vitro and in vivo. This proposal focuses on two aspects of T1 D that urgently need to be studied: the initiation of autoimmunity and its control, and the nature of the APCs that are at the center of these processes. As such, the work has the potential of being paradigm shifting and is likely to make new therapeutic approaches emerge. Project Summary/Abstract