Analysis of T cell receptor repertoire and antigen reactivity of islet infiltrating regulatory T cells in type 1 diabetes.

Multiple studies suggest that the strength of the T cell receptor (TCR) signal leading to regulatory T cell (Treg) development and function is unique and distinct from effector T cells (Teffs). However, functional implications of a unique Treg TCR repertoire in autoimmune diabetes are largely unknown. We have recently shown that the strength of TCR signaling in islet infiltrating Tregs modulates their functional profile and regulatory capacity. We hypothesize that distinct TCR repertoires of islet infiltrating Tregs have intrinsic functional differences, and this leads to differential signaling between Teffs and Tregs. Consistent with this hypothesis, islet infiltrating insulin specific Tregs exhibit increased TCR signaling, based on Nur77-GFP reporter of TCR activation.To address this hypothesis, we are characterizing TCR repertoire, function, and signaling characteristics of islet infiltrating Treg TCRs.We were able to obtain the profile of Treg and Teff TCR repertoires specific for a single epitope by isolating and sequencing insulin tetramer binding Teffs and Tregs from islets of NOD mice expressing a fixed alpha chain of an insulin specific TCR. In this epitope-focused approach, sequencing data showed relatively high similarity (Morisita-Horn index: 0.27) between Treg and Teff TCR repertoires, where a substantial portion (46.4%) of Tregs expressed Teff TCRs. Current work is focused on comparing the in vitro and in vivo functional differences between Treg and Teff derived TCRs. Our preliminary data suggests that Treg TCRs can span a wide range of reactivity to insulin, but are more tolerant of changes at the N- and C-terminus of peptide epitope. Collectively, our data suggest that Treg and Teffs specific for a single epitope can share TCRs; however, Treg development and function is associated with increased TCR signaling and increased potential for antigenic promiscuity.