Microbiota-derived metabolic priming of CAR-T cell fitness: a translational framework for next-generation cell therapy.

Chimeric antigen receptor T-cell (CAR-T) therapy has transformed the treatment of hematologic malignancies, yet durable responses remain inconsistent and clinically significant toxicities persist. Emerging evidence identifies the gut microbiota as an extratumoral determinant of CAR-T efficacy, persistence, and toxicity. However, taxonomic signatures associated with clinical outcomes show limited reproducibility and are influenced by antibiotics, geography, diet, and methodological heterogeneity. Building on prior reviews addressing microbiome-CAR-T associations and CAR-T-cell immunometabolism separately, here we synthesize clinical, translational, and preclinical evidence into an integrated, metabolome-centered framework spanning the full CAR-T treatment and manufacturing trajectory. Broad-spectrum antibiotic exposure disrupts microbial metabolic output, depleting short-chain fatty acids, indole derivatives, and other bioactive metabolites, and has been associated with inferior clinical outcomes in several cohorts, although these associations are heterogeneous and may be confounded by baseline disease severity, systemic inflammation, and infection-related factors. Experimental studies further indicate that butyrate, valerate, inosine, indoles, and succinate modulate mitochondrial fitness, memory differentiation, epigenetic programming, cytotoxicity, and exhaustion through interconnected metabolic and receptor-mediated pathways. We propose that the gut microbiota acts as a distributed metabolic organ whose collective output shapes CAR-T-cell fitness and therapeutic response. This framework supports the development of metabolite-based biomarkers and therapeutic strategies, including microbiota-conscious antibiotic stewardship, ecosystem restoration, dietary or metabolite-based interventions, and