Intestinal Microbiota in Bone Marrow Transplantation

Abstract SCI-51

Regulators of the intestinal flora include diet, antibiotics, and importantly, intestinal inflammation. As a result, the cause-effect relationships between intestinal inflammation and changes in microbiota have been difficult to define. The success of allogeneic bone marrow transplantation (allo BMT), a standard therapy for conditions including hematopoietic malignancies and inherited hematopoietic disorders, is limited by graft-versus-host disease (GVHD) morbidity and mortality. With GVHD, vigorous activation of donor immune cells, most importantly T cells, leads to damage of the skin, liver, hematopoietic system, and gut. The major sources of immune activation are histocompatibility complex differences between donor and recipient. Combinations of chemotherapy and radiation also contribute, as damage to the intestinal epithelium results in systemic exposure to microbial products normally sequestered in the intestinal lumen. We have demonstrated in murine and human recipients of allo BMT that intestinal inflammation secondary to GVHD is associated with major shifts in the composition of the intestinal microbiota. The microbiota, in turn, can modulate the severity of intestinal inflammation. In mouse models of GVHD we observed loss of overall diversity and expansion of Lactobacillales and loss of Clostridiales. Eliminating Lactobacillales from the flora of mice prior to BMT aggravated GVHD, while reintroducing the predominant species of Lactobacillus mediated significant protection against GVHD. We then characterized the gut flora of patients during onset of intestinal inflammation due to GVHD and found patterns mirroring those in mice. We also identified increased microbial chaos soon after allo BMT as a potential risk factor for subsequent GVHD. Together, these data demonstrate regulation of flora by intestinal inflammation, and suggest that flora manipulation may reduce intestinal inflammation and improve outcomes for allo BMT recipients.