Novel regulators of GVHD revealed through microbiome and metabolome patterns across distinct intestinal regions.

Microbial dysbiosis and metabolite changes in the gastrointestinal (GI) tract have been linked to pathogenesis and severity of many diseases, including graft-versus-host disease (GVHD), the major complication of allogeneic hematopoietic stem cell transplantation. However, published studies have only considered the microbiome and metabolome of excreted stool and do not provide insight into the variability of the microbial community and metabolite composition throughout the GI tract or the unique temporal dynamics associated with different gut locations. Because such geographical variations are known to influence disease processes, we used a multi-omics approach to characterize the microbiome and metabolite profiles of gut contents from different intestinal regions in well-characterized mouse models of GVHD. Our analysis validated analyses from excreted stool, but importantly, uncovered new biological insights from the microbial and metabolite changes between syngeneic and allogeneic hosts that varied by GI location and time after transplantation. Our integrated analysis confirmed the involvement of known metabolic pathways, including short-chain fatty acid synthesis and bile acid metabolism, and identified additional functional genes, pathways, and metabolites, such as amino acids, fatty acids, and sphingolipids, linked to GI GVHD. Finally, we validated a biological relevance for one such newly identified microbial metabolite, phenyl lactate, that heretofore had not been linked to GI GVHD. Thus, our analysis of the geographic variability in the intestinal microbiome and metabolome offers new insights into GI GVHD pathogenesis and potential for novel therapeutics.