GM-CSF stimulates granulopoiesis in a congenital neutropenia patient with loss-of-function biallelic heterozygous CSF3R mutations

The failure to control both innate and adaptive immune responses in the gut has recently been implicated as a major pathogenic mechanism in the development of graft-versus-host disease (GVHD). Reduced oxygen availability in the intestine has been causally linked to gastrointestinal disease. During intestinal inflammation, increased metabolic activity of resident and infiltrating immune cells, bacteria and reduced blood flow may lead to a sharp decrease of oxygen, resulting in "inflammatory" hypoxia. The transcription factor family, hypoxia-inducible factor (HIF) originally discovered as a master regulator of the adaptive response to hypoxia, has recently emerged as a key regulator of the innate and adaptive immune responses. The HIF heterodimer consists of an oxygen-labile α subunit (HIFα) and a constitutively expressed HIF-1β subunit. Both HIF-1α and HIF-2α expression are markedly elevated in intestinal epithelial cells of patients with inflammatory bowel disease (IBD) and intestinal epithelial HIF-1 attenuates colitis in preclinical mouse models. Although HIF-2 has not been studied extensively in intestinal inflammation, it has emerged as a key regulator in intestinal iron homeostasis. Given that IBD and GVHD share many pathogenic mechanisms, we hypothesized that a sustained HIF response will protect the host intestinal epithelium from conditioning- and alloreactive T cell-induced gut damage. To determine the functional significance of intestinal epithelial HIF-1 and HIF-2 in gut GVHD, we generated conditional intestinal epithelial HIF-1α (HIF-1α ΔIE ) and HIF-2α ΔIE vil-cre knockout (KO) mice on a C57BL/6 (B6) background lacking HIF-1α or HIF-2α in the host intestinal epithelium. Using a fully MHC mismatched B10.BR (H2 k )→B6 (H2 b ) bone marrow transplant (BMT) model, loss of intestinal epithelial HIF-2 reduced the median survival time (43d) compared to wild-type (WT) recipients (58d, log-rank test, P ΔIE mice than HIF-1α ΔIE mice. Hyperplastic crypts that are characteristic of regenerating crypts after radiation-induced damage were observed in Ki67-stained ileal/jejunal sections of WT mice post-BMT whereas fewer regenerating Ki67-labeled crypts were found in both HIF-1α ΔIE and HIF-2α ΔIE mice. In control T cell depleted BM groups (WT, HIF-1α ΔIE and HIF-2α ΔIE ), Ki67 + -proliferating cells resided at the crypt base. Using quantitative real-time PCR analysis, we determined whether intestinal epithelial HIF-1 and HIF-2 differentially regulated the expression of Paneth cells and intestinal stem cell markers in the jejunum, 8d post-BMT. A 5-fold and 2-fold decrease in lysozyme (Lyz) mRNA levels occurred in WT (p ΔIE BM+T mice (p ΔIE (p ΔIE (p Disclosures No relevant conflicts of interest to declare.