The impact of immune changes induced by bone marrow transplantation on the colonization of gut microbiota following fecal microbiota transplantation

Fecal microbiota transplantation (FMT) has been reported to normalize gut microbiota balance in patients with diseases such as refractory inflammatory bowel disease. It is essential to maintain a consistent gut microbiota in healthy FMT donors. However, various environmental factors influence the maintenance of gut microbiota composition. This study aims to clarify the influence of the host immune system on FMT by conducting a combined investigation of FMT and bone marrow transplantation (BMT) in mice. Animal studies were conducted to compare how differences in the donor microbiota affect post-BMT and FMT gut microbiota development. Our results show that changes in host immunity at the time of FMT did not improve the overall bacterial colonization rate compared to FMT alone. Additionally, feces and bone marrow transplanted from the same microbiota-status donor mouse had a greater effect on the abundances of gut microbes with lower relative abundances compared to when different microbiota-status donor mice were used for BMT and FMT. In particular, the colonization rate of the mucolytic bacterium Muribaculaceae was improved, suggesting that proximity to the intestinal epithelium may influence susceptibility to the host immune system. Altogether, these results highlight the importance of the host immune system in determining FMT outcomes.