Changes in Gut Phageome and Bacteriome Following Fecal Microbiota Transfer in Patients with Intestinal Graft-Versus-Host Disease and Crohn's Disease.

Intestinal bacterial dysbiosis develops in a number of immune-mediated disorders. Fecal microbiota transfer (FMT) is considered a potentially efficient tool for restoration of the patient's gut microbiota. The aim of our study was to trace the time course of dominant bacterial populations and some Enterobacteria phages in patients with GVHD and Crohn's disease after FMT procedure. Patients and methods: We observed 12 patients with intestinal graft-versus-host disease (GVHD), and 15 persons with Crohn's disease after massive anti-infectious treatment. FMT was performed by a standard protocol using oral capsules administered for 2 days. Fecal bacteriome was assessed by 16S rRNA sequencing. Viral sequences were identified by NGS with a customized primer set. Plasma citrulline levels were measured in order to assess enterocyte damage in the patients. Results: Complete clinical response to FMT was observed in 5 of 12 GVHD patients and 10 of 15 Crohn's disease cases. Before FMT, most anaerobic Bacillota were exhausted in both Crohn's disease patients and GVHD. Following FMT, Akkermansia ratios tended to decrease within 30 days in Crohn's disease, along with higher Faecalibacteria, Romboutsia, and Dialister ratios than in GVHD, thus suggesting lesser damage to anaerobic microbiota in Crohn's disease. Increased contents of facultative anaerobes (Enterococcus and E. coli) was detected in GVHD patients after FMT. Fecal virome changes in Crohn's disease after FMT included early transient decrease in Caudoviricetes with a rise in Lederbergvirus and Eganvirus ratios at later terms. In GVHD patients, reverse correlations were revealed between E. coli and E. coli-hosted Eganvirus species. Intestinal damage assessed by low plasma citrulline levels was associated with fecal Klebsiella expansion, being more pronounced in GVHD than in Crohn's disease. Clinical response to FMT in GVHD patients correlated with increased plasma citrulline and lower Eganvirus abundance. Future studies will concern specific relations between fecal bacteriome and virome reconstitution following FMT in gut GVHD and other immune-mediated intestinal disorders.