Deciphering and Visualizing Epitope Spreading in Autoimmune Diabetes

Type 1 diabetes results from a polyclonal T cell-mediated immune response against multiple beta-cell antigens, leading to the ultimate destruction of insulin-producing beta-cells. Although few self-antigens
appear to be involved initially, the autoimmune response eventually spreads to numerous other epitopes. This diversification of the immune response poses an obvious challenge to antigen-specific therapeutic
approaches that are pursued as a safer alternative to general immunosuppression. Although epitope spreading is common to several autoimmune diseases, its mechanism is not completely elucidated. In
particular, it is not clear how poorly responsive T cell clones that escaped thymic selection manage to be activated in the periphery and contribute to islet infiltration and destruction, although it is now clear that
some of them are more efficiently activated upon recognizing a modified form of their epitope. We hypothesize that successfully activated T cell clones can boost the immunogenic function of DCs such that these are now able to stimulate low affinity T cells in the context of “antigen linkage”, whereby all the T cell players are brought together around a common DC that co-express all the relevant epitopes. Using a novel
polyclonal adoptive transfer model with traceable diabetogenic T cell clones, we propose to test whether linked cooperation can indeed support the activation of low affinity T cells. We will evaluate how these
diabetogenic T cells, with varying degrees of antigen responsiveness, get stimulated in vivo when they are transferred alone or as a mixed populations and allowed to influence one another within DC clusters. The functional analysis of the activation of these different T cells will help determine whether help takes place and whether this help requires linkage (via DCs). To demonstrate that these different T cell clones
concomitantly interact with the same DCs, we will conduct intra-vital microscopy imaging of fluorescently labeled DCs and T cells to observe the formation of DC clusters in real-time and document their clonal
composition and dynamic. These studies will help design therapeutic strategies aimed at reversing this phenomenon using linked suppression by regulatory T cells.