Gastrointestinal microbiome changes in patients with multiple myeloma during the course of autologous hematopoietic stem cell transplantation

The concept of high-dose chemotherapy followed by transplantation of hematopoietic stem cells (HSCT) remains the standard for treating multiple myeloma (MM). Unfortunately HSCT is frequently associated with severe toxicities, including graft-versushost disease (GVHD), gastrointestinal mucositis, and opportunistic infections. Since the 1970s, the microbiome specifically, intestinal microbiota and their metabolites have been recognized as key mediators of allogeneic HSCT outcomes, including GVHD and overall survival (OS). Despite the rapidly accumulating evidence, that the fecal bacteriome plays a key role in allogeneic HSCT, less is known about its role in the context of autologous HSCT. We studied the changes in gastrointestinal bacteriome in 15 adult patients (9 women, 6 men, aged 54-66 years) with multiple myeloma, who underwent autologous HSCT. A significant (p=0,0215) decrease in the microbiota diversity index was revealed in the period after HSCT. We observed a continuous decrease in gastrointestinal microbiome diversity, until 35 days after HSCT. We found the significant decrease in relation to the Actinobacteria phylum (p=0.0348). No significant changes in the level of other studied phyla Bacteroides, Firmicutes, Proteobacteria were found. Also we found that microbiome composition present is associated with the incidence and severity of post-transplant toxicity (especially nausea and vomiting), and culture-negative neutropenic fever.