PROJECT 1 SUMMARY: Mucin-preserving strategies to reduce allo HCT toxicities Allogeneic hematopoietic cell transplantation (allo HCT) is a standard therapy for a variety of benign and malignant hematological diseases. Despite ongoing advances, it remains a high-risk treatment modality, due in large part to the risk of developing graft-versus-host disease (GVHD), a severe inflammatory condition that commonly afflicts the intestinal tract and can lead to considerable morbidity and mortality. Work from multiple groups over the past decade have demonstrated that gut microbiota (GM) injury commonly precedes GVHD and subsequent treatment-related mortality (TRM). The most common source of GM injury in allo HCT patients are antibiotics, which are given to treat life- threatening infections that commonly arise in these immune-compromised patients. We recently reported (Hayase, et al, Cell, 2022) that one antibiotic, meropenem, is both associated with increased intestinal GVHD in allo HCT patients and can aggravate experimental GVHD in mouse models. One major mechanism appears to be antibiotic-mediated selection of mucus-degrading Bacteroides, which then leads to erosion of colonic mucus and increased bacterial translocation. Neutropenic fever is another common toxicity of all HCT, and we recently published our findings that Akkermansia and Bacteroides, both of which can degrade mucins, were associated with development of neutropenic fever (Schwabkey, et al, Sci Transl Med, 2022). Experiments in mice with antibiotic-mediated depletion of these bacteria, as well as re-introduction of these bacteria, demonstrated that Akkermansia and Bacteroides species synergize to produce thermodysregulation and compromise intestinal mucus in mouse models of HCT conditioning. In preliminary experiments, have begun to characterize the individual contributions of Akkermansia and Bacteroides to intestinal GVHD, and have also identified conditions which lead to their expansion and upregulation of mucus-degrading enzymes. Based on this knowledge, we are developing non-antibiotic strategies to suppress mucus-degrading behavior by these otherwise usually benign commensal bacteria. In this Project, we will further explore the diet-microbiota-mucin axis is a targetable modifier of intestinal GVHD risk. Our Aims are: 1) To examine how mucus-degrading intestinal bacteria are associated with intestinal GVHD, and 2) To examine potential efficacy of novel translational strategies to target mucus- degrading intestinal bacteria in reducing GVHD. Strategies include oral administration of xylose, propionate, and the naphthoquionone MNQ.