Gastrointestinal Microbiome and Mycobiome changes during Autologous Transplantation for Multiple Myeloma: Results of a Prospective Pilot Study

Abstract Microbiome dysbiosis has been associated with adverse hematopoietic cell transplantation outcomes. We hypothesized that exposure to high-dose melphalan and antimicrobials in patients undergoing autologous HCT for plasma cell disorders results in oral and gastrointestinal microbial dysbiosis that is in turn associated with regimen-related toxicities. We conducted a prospective study describing the longitudinal changes in oral and gastrointestinal bacteriome and mycobiome in this patient population. Our study showed that microbiome composition present at baseline is associated with the incidence and severity of post-transplant nausea, vomiting, culture-negative neutropenic fevers and rates of neutrophil engraftment. We also have evidence of an association between the microbial communities at count nadir and the development of regimen-related gastrointestinal toxicities commonly observed after exposure to high-dose melphalan. While bacteriome diversity largely recovers a month after transplantation, we observed a continuous decrease in oral and gastrointestinal mycobiome diversity suggesting that the mycobiome requires a longer time to recover compared to the bacteriome after transplantation.