Fecal microbiota transplantation enhanced the effect of chemoimmunotherapy by restoring intestinal microbiota in LLC tumor-bearing mice.

OBJECTIVE: To assess the effect of half-dose chemotherapy (HDC) and standard-dose chemotherapy (SDC) on the intestinal microbiota and to investigate whether fecal microbiota transplantation (FMT) can restore the intestinal microecology to enhance the efficacy of chemoimmunotherapy containing an anti-PD- 1 antibody (PD1). METHODS: Lewis lung cancer (LLC) tumor-bearing mice were divided into six groups, including Control, HDC, SDC, SDC + FMT, SDC + PD1, and SDC + PD1 + FMT. After the treatment, analyses were conducted on intestinal microbiota using 16S rRNA sequencing, immune cells through flow cytometry, cytokines and chemokines via polymerase chain reaction (PCR), and programmed death-ligand 1 (PD-L1) expression in tumor tissues by immunohistochemistry. RESULTS: Alpha and beta diversity of intestinal flora were not significantly different between HDC and SDC groups, nor was there a significant difference in the abundance of the top 10 species at the phylum, class, order, family, genus, or species levels. FMT increased both alpha and beta diversity and led to an increase in the abundance of Ruminococcus_callidus and Alistipes_finegoldii at the species level in mice receiving SDC + FMT. Besides, tumor growth was significantly slowed in SDC + PD1 + FMT compared to SDC + PD1 group, accompanied by an up-regulated Bacteroidetes/Firmicutes ratio, down-regulated abundance of Proteobacteria species (including Pseudolabrys, Comamonas, Alcaligenaceae, Xanthobacteraceae and Comamonadaceae), as well as Faecalicoccus of Firmicutes, the increased number of cDC1 cells, cDC2 cells, CD4(+) T cells and CD8(+) T cells in the peripheral blood, and IFN-γ(+)CD8(+) T cells, IFN-γ, granzyme B, TNF-α, CXCL9 and CXCL10 in intestinal tissues. CONCLUSIONS: There were no significant differences between HDC and SDC in their effects on the intestinal microbiota. FMT exhibited a beneficial impact on gut microbiota and improved the efficacy of chemoimmunotherapy, possibly associated with the increase of immune cells and the modulation of related cytokines and chemokines.