Microbiome and metabolite biomarkers of CAR T-cell therapy outcomes in relapsed/refractory diffuse large B-cell lymphoma.

CD19 chimeric antigen receptor (CAR) T-cell therapy has revolutionized treatment for relapsed/refractory diffuse large B-cell lymphoma (R/R-DLBCL), but challenges such as posttreatment failure and immune-related adverse events (AEs) persist. This study explores the gut microbiome as a predictive biomarker for CAR T-cell therapy outcomes and toxicity. Stool and serum samples from patients with R/R-DLBCL were analyzed at apheresis (47 samples) and 1 month after infusion (32 samples) using whole-genome sequencing metagenomics. When compared with healthy controls and newly-diagnosed DLBCL, R/R-DLBCL showed significant gut dysbiosis, characterized by increased Proteobacteria and Enterobacteriaceae. Responders had higher levels of Bacteroides fragilis, whereas nonresponders exhibited higher levels of Faecalibacterium prausnitzii. Functional metagenomic analysis suggested enrichment of inosine biosynthesis pathways in responders, and elevated serum inosine demonstrated an exploratory association with improved progression-free survival. Distinct microbial taxa and serum fatty acid profiles were also linked to CAR T-cell-related AEs, with higher acetate and butyrate levels in patients without AEs and increased isovalerate in those with AEs. These findings indicate that gut microbiome features-particularly Bacteroides fragilis and inosine metabolism-may serve as candidate biomarkers for CAR T-cell therapy outcomes and toxicity. However, given the exploratory nature of these analyses and the limited cohort size, results should be interpreted cautiously. Larger, prospective studies will be required to validate these observations and to assess the potential of microbiome-based strategies to optimize CAR T-cell therapy in R/R-DLBCL.