Mechanisms Controlling the Development and Function of Intestinal Effector Treg cells - PROJECT SUMMARY Mechanisms Controlling the Development and Function of Intestinal Effector Treg Cells. The pathogenesis of a spectrum of disorders referred to as inflammatory bowel disease (IBD) is characterized by immune dysregulation to components of the enteric microbiota. Findings from mouse and man highlight a critical, non-redundant role for the immunoregulatory cytokine IL-10 in maintenance of intestinal immune homeostasis. Our labs have shown that Foxp3+ regulatory T (Treg) cells are, overwhelmingly, the major source of IL-10 in the intestines, where many of these cells co-express the canonical “Th17” transcription factor, RORγt—particularly in large intestine (LI). However, IL-10 is only produced by a subset of Treg cells—defined as ‘effector’ (e)Treg cells. Mechanisms that control the development of eTreg cells are incompletely understood. The premise of this application, founded on recent discoveries from, and synergy between, the two PIs (Weaver, Hatton) is that heretofore unappreciated interplay between signaling pathways of the IL-2 and TNF superfamilies has a central role in regulating the development and function of eTreg cells in the intestines. Specifically, we have identified the TNF receptor superfamily signaling pair, TNFSF15-TNFRSF25 (TL1A-DR3), as an important amplifier of the transition of “central” (c)Treg cells into eTreg cells and propose that this pathway plays an important role in calibrating IL-2–driven control of the Treg cell program via multiple mechanisms. We hypothesize that the TL1A- DR3 pathway is non-redundant in its regulation of IL-2 receptor (IL-2R) signaling to modulate the size and cTreg– eTreg balance of the LI Treg cell pool both at homeostasis and under inflammatory conditions. Further, we posit that DR3 acts through multiple mechanisms to alter output of the IL-2R to regulate development of IL-10– producing eTreg cells. We propose that a major driver of eTreg cell development is increased STAT3 output of the IL-2R, which is enhanced by actions of DR3 to: (i) increase sensitivity of the IL-2R; and (ii) decrease pSTAT3 degradation, thereby altering the IL-2–induced STAT5/STAT3 ratio. Finally, we propose that other TNFRSF members contribute to eTreg cell maintenance after DR3 expression declines. We test this hypothesis through complementary, but not inter-dependent, Aims, leveraging: a novel method for generating stable, colitis-curing Treg cells ex vivo; new approaches for efficient gene knock-downs in primary T cells; and new gene-targeted mouse models to define mechanisms governing the convergence of these signaling pathways in controlling the transcriptional regulation of Il10 and the eTreg program. Successful completion of these Aims will establish new biological paradigms and inform novel therapeutic approaches by which endogenous IL-10 can be up-regulated and the differentiation and function of eTreg cells enhanced to treat human IBD.
