Abstract
Immune checkpoint blockade therapy with anti-PD-1 monoclonal antibody (mAb) is a treatment for colorectal cancer (CRC). However, some patients remain unresponsive to PD-1 blockade. The gut microbiota has been linked to immunotherapy resistance through unclear mechanisms. We found that patients with metastatic CRC who fail to respond to immunotherapy had a greater abundance of Fusobacterium nucleatum andincreased succinic acid. Fecal microbiota transfer from responders with low F.nucleatum, but not F.nucleatum-high non-responders, conferred sensitivity to anti-PD-1 mAb in mice. Mechanistically, F.nucleatum-derived succinic acid suppressed the cGAS-interferon-β pathway, consequently dampening the antitumor response by limiting CD8+ Tcell trafficking to the tumor microenvironment (TME) invivo. Treatment with the antibiotic metronidazole reduced intestinal F.nucleatum abundance, thereby decreasing serum succinic acid levels and resensitizing tumors to immunotherapy invivo. These findings indicate that F.nucleatum and succinic acid induce tumor resistance to immunotherapy, offering insights into microbiota-metabolite-immune crosstalk in CRC.
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