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, RORt—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.