Fasting-mimicking diet-enriched Bifidobacterium pseudolongum suppresses colorectal cancer by inducing memory CD8 + T cells

Background Fasting-mimicking diet (FMD) boosts the antitumour immune response in patients with colorectal cancer (CRC). The gut microbiota is a key host immunity regulator, affecting physiological homeostasis and disease pathogenesis. Objective We aimed to investigate how FMD protects against CRC via gut microbiota modulation. Design We assessed probiotic species enrichment in FMD-treated CRC mice using faecal metagenomic sequencing. The candidate species were verified in antibiotic-treated conventional and germ-free mouse models. Immune landscape alterations were evaluated using single-cell RNA sequencing and multicolour flow cytometry. The microbiota-derived antitumour metabolites were identified using metabolomic profiling. Results Faecal metagenomic profiling revealed Bifidobacterium pseudolongum enrichment in FMD-treated CRC mice. B. pseudolongum mediates the FMD antitumour effects by increasing the tissue-resident memory CD8 + T-cell (TRM) population in CRC mice. The level of L-arginine, a B. pseudolongum functional metabolite, increased in FMD-treated CRC mice; furthermore, L-arginine induced the TRM phenotype in vivo and in vitro. Mechanistically, L-arginine is transported by the solute carrier family 7-member 1 (SLC7A1) receptor in CD8 + T cells. Both FMD and B. pseudolongum improved anti-CTLA-4 efficacy in the orthotopic mouse CRC model. In FMD-treated patients with CRC, the CD8 + TRM cell number increased as B. pseudolongum and L-arginine accumulated. The abundance of CD8 + TRM cells and B. pseudolongum was associated with a better prognosis in patients with CRC. Conclusion B. pseudolongum contributes to the FMD antitumour effects in CRC by producing L-arginine. This promotes CD8 + T-cell differentiation into memory cells. B. pseudolongum administration is a potential CRC therapeutic strategy.