Th17/Treg in Human Graft-Versus-Host-Disease (GvHD) of the Gastro-Intestinal (GI) Tract
Authors: Socie Gerard , Ratajczak Philippe , Leboeuf Christophe , Desveaux Allisson , de Latour Regis Peffault , Robin Marie , Mary Jean Yves , Janin Anne 
Published: October 2019

Abstract
Background; The recent discovery of CD4+ characterized by secretion of IL-17 (Th17) and the regulatory Foxp3 CD4 cell (Treg) has had a major impact on our understanding of immune processes. Th17 and Treg have been implicated in the pathogenesis of human autoimmune disease, including inflammatory bowel disease (IBD). Data from murine model of autoimmune disease suggest that there is a reciprocal relationship between Th17-induced pathology and Treg regulatory role which prevent tissue inflammation and mediate self-tolerance. Today few murine data have been published on the role of Th17 in GvHD and, to the best of our knowledge, none in human GvHD.
Aim; We took the advantage of stored biopsies from one of our previous study on human GI GvHD (Blood2004; 103: 50–57), to look for the expression of Il-17 and of Foxp3 in CD4+ cells in the same biopsies we previously studied.
Methods; In addition to characterization and quantification of the cellular infiltrate, TNF, TNF receptors, and Fas in situ expression analyses, quantification of apoptotic cell numbers by TUNEL, double immunohistochemistry staining and quantification of CD4+/IL17+ cells (Th17) and of CD4+/Foxp3+ cells (Treg) was analyzed. The sensitivity and specificity of the Th17/ Treg ratio to the clinico-pathological diagnosis of GvHD and the correlation of this ratio to previously described parameters (Blood2004; 103: 50–57) were then analyzed.
Results; 40 patients (pts) with suspected GvHD of the GI tract (nausea/vomiting or diarrhea) were enrolled and had biopsies before any steroid treatment. All underwent transplantation after a myeloablative conditioning regimen. 18 pts had severe pathological grade GvHD. The density of CD4+ expressing IL-17 or Foxp3 was not high needing high magnification for quantitative estimates; the numbers of Th17 cells per field range from 0 to 8 per field with a median of 1(IQR 0.25-4), and that of Treg was 4 (range 0–11, IQR 1–6), with a mean Th17/ Treg ratio of ½. The number of Th17 cells in patients with pathologically proven GvHD ranged between 0 and 2 in 27pts, even in 15/18 pts with pathological grade 2. On the contrary, among 34 patients with pathological GvHD median of 5 Treg cells per field was found. A Th17/ Treg ratio< 1 correlated both with the clinical diagnosis (sensitivity 64%, specificity 94%, p<.001), and pathological grade (sensitivity 63.6%, specificity 94.4%, p=.002). When correlation was done with other parameters, the Th17/ Treg ratio<1 also correlated with the intensity of apoptosis of epithelial cells (p=.0006) as assessed by quantitative TUNEL essay, Fas expression in the cellular infiltrate (p=.002) and interestingly highly correlated with TNF and TNF receptors 1 and 2 expression (p<.001 far all).
Conclusions; Contrary to IBD models and few clinical data in pts with rheumatoid arthritis and Crohn’s disease our data do not support increased tissue damage associated with Th17 presence in human GvHD of the GI tract. However our data perfectly fit with a recent study in a murine model of GvHD demonstrating that absence of donor Th17 exacerbated acute GvHD (Blood Prepublished Jul 2, 2008; doi:10.1182/blood-2007-12-126987).