Benaroya Research Institute Seattle, Washington, United States
Abstract Text: It has been suggested that Treg repress PI3k-Akt-mTOR signaling pathway and excessive activation of this pathway is deleterious to suppressive function of Treg. Previously, we observed an inverse relationship between TCR functional avidity and antigen-specific suppressive activity of T cells engineered to constitutively express FOXP3 (EngTregs). Here we investigated how TCR signal strength affects the function of islet antigen specific EngTregs in the context of antigen-stimulation and how TCR avidity differentially impacts signaling in EngTregs and nTreg. We found that both EngTregs and nTreg expressing a low avidity TCR maintained reduced activation of PI3K-Akt-mTOR pathway and EngTregs with a low avidity TCR suppressed polyclonal islet antigen-specific Teff better than nTreg with the same low avidity TCR despite the similarity in TCR signaling. However, EngTregs expressing a high avidity TCR displayed increased activation of both mTORC1 and mTORC2 signaling pathways, produced inflammatory cytokines, expressed high levels of Tbet, and showed poor suppression of polyclonal islet antigen specific responses. By contrast, nTreg expressing the same high avidity TCR had impaired mTORC2 pathway signaling and showed superior suppressive capacity compared to nTreg expressing the low avidity TCR. Our study demonstrates that TCR avidity differentially affects signaling and suppressive function of EngTregs and nTreg, suggesting intrinsic differences between EngTregs and nTreg independent of FOXP3 expression that alter function in response to the strength and character of TCR signaling. These findings have implications in the future design of engineered Treg therapeutics.
