Intratumoral microbiota-derived S1P sensitizes the combination therapy of Capecitabine and Nivolumab

Clinical responses of colorectal cancer (CRC) treatments vary considerably due to the heterogeneity of tumor micro-environment (TME), where intratumoral microbiota may reshape the unique inflammation imprints. However, its complex mechanistic underpinnings remain incompletely elucidated. Herein we sought to delineate the critical role of intratumoral microbiota in potentiating combination therapeutics against CRC. By comparing germ-free (GF) and specific pathogen-free (SPF) mouse models of 33 potential CRC treatments, we screened out the combination regimen of Capecitabine-Nivolumab significantly augmented by intratumoral microbiota in tumor regression and survival prolongation. The enrichment of Bacteroides fragilis induced by Capecitabine-Nivolumab was concomitant with elevated microbial sphingosine-1-phosphate (S1P), which further upregulated tumoral PD-L1 expression by enhancing histone deacetylation at the CD274 locus. Activation of microbial sphingosine kinase 2 (SphK2) ultimately led to an expansion of effector memory CD8 ⁺ T cells and reduction of exhausted T cell subsets within TME. To conclude, these findings advance our understanding of the intricate interplay among intratumoral microbiota, sphingolipid metabolites and immunochemotherapeutics. It highlights microbial sphingolipids as potential predictive biomarkers for strategies of targeting intratumoral microbiota in CRC management.