Science Spotlight

Commensals turn pathogenic in graft-vs-host disease

From the University of Michigan and the Fredricks Lab, Vaccine and Infectious Disease Division 

Butyrate is a short-chain fatty acid that is naturally produced in the gut through microbial fermentation of dietary fibers and serves as an energy source for colonic epithelial cells. Despite the beneficial properties of butyrate during homeostasis, the role of butyrate-producing bacteria in conditions such as graft-versus-host disease (GVHD) after allogeneic stem cell transplant (HCT) remains unclear, as previous studies have reported both beneficial and deleterious roles for butyrate in the development of chronic and steroid-refractory GVHD. To interrogate this relationship, Dr. Jonathan Golob from the University of Michigan, along with collaborators from the Public Health Sciences, Clinical Research, and Vaccine and Infectious Disease Divisions, used a cohort of HCT patients to assess the risk of GVHD colitis with and without the presence of butyrogenic gut bacteria. They recently published this work in Blood Advances.

The authors collected weekly stool specimens for 100 days from an HCT cohort undergoing allogeneic HCT, and performed 16S rRNA gene sequencing to determine the presence and relative abundance of butyrogenic bacteria in the gut of a given patient. Retrospectively, they reviewed each patient’s medical chart to assess whether a patient developed steroid-refractory or chronic gut GVHD after HCT. Of the 210 HCT recipients in the cohort, 27 initially developed acute GVHD, with four and 11 of these going on to develop chronic or steroid-refractory GVHD. Comparing the bacteria present in the gut in those who developed more serious GVHD, the authors noted a significant association between the development of chronic or steroid-refractory GVHD and butyrogenic bacteria presence in the gut within 21 days of the onset of acute GVHD. 

The intestinal epithelial environment during homeostasis, GVHD, and recovery phases with (both) and without (top) butryogenic bacteria.
The intestinal epithelial environment during homeostasis, GVHD, and recovery phases with (both) and without (top) butryogenic bacteria. Figure provided by Dr. Amy Chang.

After finding that their data suggested that butyrogenic bacteria increased the risk of chronic or steroid-refractory GVHD, the authors further investigated the mechanism underlying butyrate and gut inflammation. Previous studies have shown that butyrate inhibited healing of the gut epithelium by suppressing colonic stem cells in a murine model of colitis, a condition defined by chronic intestinal inflammation that closely mimics gut GVHD. However, it has not been shown how butyrate affects human colonic progenitor cells. The authors plated colonoids, an ex vivo model of the colon epithelium comprised of primary human stem cells, onto transwells. In this model, the epithelium forms a monolayer between the chambers due to the tight junctions associated with epithelial differentiation, and epithelial integrity can be measured by transepithelial electrical resistance (TEER). The authors added butyrate to the colonoid and found that its presence led to a loss of tight junctions in the epithelial barrier over several days, as measured by the absence of TEER, compared to high TEER measured in colonoid monolayers that did not receive butyrate. These findings suggested that butyrate weakens the human intestinal barrier, possibly explaining why the presence of butryogenic bacteria in the gut is associated with an inability to resolve GVHD.

This was the first study relating the gut microbiome with the risk for steroid-refractory colitis with graft versus host disease,” Golob explained. “Microbes that make butyrate are found in all healthy adult guts, but only in some people after hematopoietic stem cell transplant. In the transplant recipients who went on to develop severe graft versus host disease of the gut (in which the transplanted immune cells attack the recipient), the presence of butyrate generating bacteria predicted those whose colitis would fail to respond to the best available treatment: high dose steroids. We used an in vitro model of the human gut to show why: gut stem cells are blocked from forming an intact gut barrier when exposed to butyrate.” This relationship may explain some of the discrepancies in past research, as their “results show that microbe-host interactions that are beneficial in health (butyrate production) can be harmful in specific disease states. The contextuality of host-microbiome interactions is underexplored,” Golob said. “For patients with steroid-refractory graft versus host disease after transplant, we have no good treatment. Patients in this situation die at a very high rate from the graft versus host disease. With future studies, we could offer patients with steroid-refractory graft versus host disease a new treatment: changing their gut microbiome.”

This work was supported by private donor funds, National Institutes of Health, National Institute of Allergy and Infectious Diseases, and the American Society for Transplantation and Cellular Therapy New Investigator Award.

UW/Fred Hutch Cancer Consortium members David Fredricks, Marco Mielcarek, Steven Pergam, Michael Wu contributed to this work.

Golob JL, DeMeules MM, Loeffelholz T, Quinn ZZ, Dame MK, Silvestri SS, Wu MC, Schmidt TM, Fiedler TL, Hoostal MJ, Mielcarek M, Spence J, Pergam SA, Fredricks DN. 2019. Butyrogenic bacteria after acute graft-versus-host disease (GVHD) are associated with the development of steroid-refractory GVHD. Blood Advances. DOI: 10.1182/bloodadvances.2019000362