AUTHOR=Buchele Vera , Abendroth Benjamin , Büttner-Herold Maike , Vogler Tina , Rothamer Johanna , Ghimire Sakhila , Ullrich Evelyn , Holler Ernst , Neurath Markus F. , Hildner Kai 

TITLE=Targeting Inflammatory T Helper Cells via Retinoic Acid-Related Orphan Receptor Gamma t Is Ineffective to Prevent Allo-Response-Driven Colitis

JOURNAL=Frontiers in Immunology

VOLUME=Volume 9 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2018.01138

DOI=10.3389/fimmu.2018.01138

ISSN=1664-3224

ABSTRACT=Intestinal Graft-versus-host disease (GvHD) is a life-threatening, inflammatory donor T cell-mediated complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the light of the reported efficacy of interleukin 23 (IL-23)-blockade to mitigate syngeneic intestinal inflammation in inflammatory bowel disease (IBD) patients, targeting IL-23 and thereby interleukin 17a (IL-17a) producing T helper cells (Th17) as the T cell subset assumed to be mostly regulated by IL-23, has emerged as a putatively general concept to harness immune-mediated mucosal inflammation irrespective of the underlying trigger. However, the role of Th17 cells during allo-response driven colitis remains ambiguous due to a series of studies with inconclusive results. Interestingly, we recently identified GM-CSF+ (granulocyte-macrophage colony-stimulating-factor) T cells to be promoted by interleukin-7 (IL-7) signaling and controlled by the activating protein-1 (AP-1) transcription factor family member BATF (basic leucine zipper transcription factor ATF- like) as critical mediators of intestinal GvHD in mice. Given the dual role of BATF, the contribution of IL-23-mediated signaling within donor T cells and bona fide Th17 cells remains to be delineated from the regulation of GM-CSF+ T cells in the absence of BATF. Here, we found in a complete MHC class I-mismatched model that genetic inactivation of the IL-23 receptor (IL-23R) or the transcription factor RORt (retinoic acid-related orphan receptor gamma t) within donor T cells similarly ablated Th17 cell formation in vivo but preserved the T cells’ ability to induce intestinal GvHD in a compared to wildtype controls indistinguishable manner. Importantly, RORt-independent manifestation of intestinal GvHD was completely dependent on BATF-regulated GM-CSF+ T cells as BATF/RORt double-deficient T cells failed to induce colitis and the antibody-mediated blockage of IL-7/IL-7R interaction and GM-CSF significantly diminished signs of intestinal GvHD elicited by RORt-deficient donor T cells. Finally, in analogy to our murine studies, colonic RORC expression levels inversely correlated with the presence of GvHD in allo-HSCT patients.
Together, this study provides a crucial example of a BATF-dependent, however IL-23R signaling- and RORt-, i.e. Th17 fate-independent regulation of a colitogenic T cell population critically impacting the current understanding of intestinal GvHD.