The role of intestinal antimicrobial and inflammatory molecules in acute graft-versus-host disease

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Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for different hematological malignancies. Acute graft-versus-host disease (aGVHD), relapse and infections are the major life-threatening complications after allo-HCT. We reported that activation of the innate immune system, in particular neutrophil granulocytes (neutrophils), is an early step in the pathogenesis of aGVHD. Neutrophil migration and MHC-II expression were reduced by JAK1/2 inhibition. Our previous work had shown that JAK1/2 inhibition reduced aGVHD in mice and in patients, proven by a multicenter phase III trial. While neutrophils that occurred in the early phase after allo-HCT were pro-inflammatory, our preliminary data indicate that neutrophils that occur in the lamina propria of mice with healing GVHD may promote tissue repair and reduce inflammation. Using single cell RNA sequencing on neutrophils residing in the intestinal tract at late time points after allo-HCT when GVHD is healing, we identified multiple antimicrobial and inflammatory molecules in neutrophils including the antimicrobial glycoprotein Lipocalin-2 (LCN2), that is known to limit bacterial growth. Our preliminary data indicate that LCN2 treatment reduced GVHD-related mortality and macrophages exposed to LCN2 produced multiple molecules that reduce T cell activation including arginase-1. In this proposal we plan to determine the role of LCN2 for the healing process in late acute GVHD. A particular focus will be on the regulation of inflammatory, antimicrobial and immunosuppressive molecules production, induced via LCN2 in intestinal macrophages. We hypothesize that LCN2-induced arginase-1 production reduces allo-reactive T cell activation in the intestines, thereby allowing the epithelium to heal. Additionally we wish to evaluate the impact of LCN2 on the intestinal microbiome composition, on metabolic activity of donor T cells and on graft-versus-leukemia effects. To clarify if the results from the murine setting can be transferred into the human situation, we will determine the level of LCN2 in different cell types residing in human intestinal tissues with or without active GVHD and healing GVHD. Additionally we will analyze the tissues for LCN2, arginase-1 and 24p3R / SLC22A17 in patients undergoing allo-HCT with the prospect to clarify if these correlate with SR-GVHD and non-relapse mortality. Overall this project aims at determining the role of LCN2 and other antimicrobial and inflammatory molecules in GVHD to better understand the GVHD healing process and to develop potential novel treatments for patients with GVHD.