Parabacteroides distasonis promotes CXCL9 secretion of tumor-associated macrophages and enhances CD8T cell activity to trigger anti-tumor immunity against anti-PD-1 treatment in non-small cell lung cancer mice.

BACKGROUND

Parabacteroides distasonis (P. distasonis) could regulate inflammatory markers, promote intestinal barrier integrity, and block tumor formation in colon. However, the regulatory effect of P. distasonis on non-small cell lung cancer (NSCLC) remains unknown. This study aimed to investigate the regulatory effect of P. distasonis on NSCLC and its impact on tumor immunity.

METHODS

We first established a mouse model of Lewis lung cancer, and administered P. distasonis and intrabitoneal injection of anti-mouse PD-1 monoclonal antibody to assess the impact of P. distasonis on tumor immunity, and mouse intestinal barrier. Then, we explored the effect of P. distasonis on CD8T cells and CXCL9 secretion mediated by tumor-associated macrophages (TAM). We used the TLR1/2 complex inhibitor CPT22 to evaluate its effect on macrophage activation. Finally, we explored the effect of P. distasonis on CD8T cells and CXCL9 secreted by TAM in vivo.

RESULTS

In vivo, P. distasonis enhanced anti-tumor effects of anti-PD-1 in NSCLC mice, improved intestinal barrier integrity, recruited macrophages, and promoted M1 polarization. In vitro, CD86 and iNOS levels in BMDM were elevated and CD206 and Arg1 levels were suppressed in membrane fraction of P. distasonis (PdMb) group in comparison to Control group. With additional CPT22 pre-treatment, the levels of CD86 and iNOS in BMDM were reduced, and the levels of CD206 and Arg1 were increased. Compared to PBS group, P. distasonis group exhibited higher proportion of CD8T cells in tumor tissues, along with increased positive proportion of GZMB and IFN-γ in CD8T cells. Additionally, in comparison to Control group, PdMb group showed an elevated proportion of GZMBT and IFN-γT cells within CD8T cells, and secretion of IFN-γ, TNF-α, perforin, and GZMB in CD8T cell supernatant increased. Moreover, the proportion of CXCL9F4/80 macrophages in tumor tissues was higher in P. distasonis group compared to PBS group. In comparison to Control group, CXCL9 protein level in BMDM and CXCL9 secretion level in BMDM supernatant were increased in PdMb group. Finally, P. distasonis enhanced CD8T cell activity by secreting CXCL9 from macrophages in vivo.

CONCLUSIONS

P. distasonis promoted CXCL9 secretion of TAM and enhanced CD8T cell activity to trigger anti-tumor immunity against anti-PD-1 treatment in NSCLC mice.