Tu124 - Thymic Selection of Multiple T1D-Associated HLA Class II-Restricted Human T Cells

Abstract Text: Type 1 diabetes (T1D) is a chronic autoimmune disease driven by autoreactive T cells that target insulin-producing beta cells. To investigate the thymic development and selection of such T cells, we used human immune system mice generated with human fetal hematopoietic stem cells and thymus tissue. We studied the development of six potentially diabetogenic T cell clones expressing HLA-DQ8 or HLA-DR4-restricted T cell receptors (TCRs) reactive to InsB9-23, InsC9-17, InsC10-18, InsC/IAPP2 hybrid insulin peptide (HIP), and GAD65555-567.

Flow cytometric analysis revealed distinct thymic selection outcomes across these clones, with varying levels of partial deletion, regulatory T cell (Treg) conversion, or peripheral escape. Clone 5 and clone 20D11 T cells, reactive to InsB9-23, underwent efficient negative selection or Treg conversion, as previously reported, indicating antigen encounter during thymic development. Interestingly, the InsC9-17-reactive clone A5.5, but not the InsC10-18-reactive clone A1.9, generated Tregs, reflecting either differences in TCR affinity for the cognate peptide or in proteolysis products of the C-chain in thymic antigen-presenting cells. No Treg conversion was observed for the HIP-reactive clone A3.10 and the GAD65555-567-reactive clone R164, suggesting a lack of thymic antigen presentation.

Analysis of scRNA-seq and TCR sequencing data from thymic tissue grafts is underway for a more comprehensive analysis of these T cell clones at different stages of development.
These findings shed light on the interplay between thymic selection and peripheral escape in T1D pathogenesis, advancing our understanding of tolerance breakdown and autoreactive T cell development in humans.