Increased abundance of <i>Firmicutes</i> and depletion of <i>Bacteroidota</i> predicts poor outcome in chronic lymphocytic leukemia

Evidence indicates that there are significant alterations in gut microbiota diversity and composition in patients with hematological malignancies. The present study investigated the oral and intestinal microbiome in patients with chronic lymphocytic leukemia (CLL) (n=81) and age-matched healthy volunteers (HVs; n=21) using 16S ribosomal RNA next-generation sequencing. Changes in both oral and gut microbiome structures were identified, with a high abundance of <i>Proteobacteria</i> and depletion of <i>Bacteroidetes</i> in CLL as compared to HVs. Oral and stool samples of patients with CLL revealed a significant change in the abundance of short-chain fatty acid-producing genera in comparison with HVs. Furthermore, the relative abundance of oral and intestine <i>Bacteroidetes</i> was significantly decreased in patients with CLL with negative prognostic features, including unmutated immunoglobulin heavy chain gene (IGHV). Notably, an increased abundance of gut <i>Firmicutes</i> was found to be associated with high expression of CD38. Finally, the present study suggested the log <i>Firmicutes/Bacteroidota</i> ratio as a novel intestinal microbiome signature associated with a shorter time to first treatment in individuals with CLL. The findings indicate that oral and gut microbial diversity in CLL might point to the inflammatory-related modulation of the clinical course of the disease.