The Gut Microbiome Drives Endogenous T-cell Activation Following CAR T-cell Therapy

Chimeric antigen receptor (CAR) T-cell therapy has become a promising clinical approach against hematologic malignancies, but patients receiving CAR T-cell therapy still present inconsistent clinical outcomes and are complicated by incomplete tumor eradication. The gut microbiome has shown a strong correlation with the therapeutic outcomes of CAR T-cell therapy. However, the underlying mechanism of how gut microbiota affect CAR T-cell therapeutic potency remains undetermined. In this study, we established a syngeneic CD19+ murine lymphoma model that allows for the evaluation of both endogenous immune cells and gut microbiota following CD19-CD28ζ CAR T-cell therapy. Using single-cell transcriptomic analyses, we report that CAR T-cell infusion led to the activation of peripheral and gut-infiltrating endogenous CD8+ T cells toward an effector-like phenotype. In parallel, 16S RNA sequencing revealed substantial alterations in gut microbiota after infusion. The composition of gut bacteria was associated with the activation status of endogenous CD8+ T cells and responsiveness to CAR T-cell therapy. More specifically, we identified gut bacteria strains Turicibacter and Parvibacter as critical determinants of effective CAR T-cell treatment. Supplementation with these species of gut bacteria during CAR T-cell therapy led to superior antitumor efficacy. Furthermore, both strains facilitated CAR T-cell therapy-induced activation of endogenous CD8+ T cells, enhancing their capability to express activation-associated surface markers as well as tumor lysis potency. In summary, our results demonstrate that the gut microbiome plays an essential role in endogenous immune activation after CAR T-cell therapy and provide specific targets for therapeutic interventions.