induced antitumor immunity and synergized with anti-programmed cell death 1 to reduce tumor burden in mice.

The gut microbiota was emerging as critical regulatory elements in shaping the outcome of cancer immunotherapy. However, the underlying mechanisms by which the gut commensal species enhance antitumor immunity remain largely unexplored. Here, we show that the gut microbiota from healthy individuals conferred considerable sensitivity to anti-PD-1 in the colorectal cancer (CRC) tumor-bearing mice, whereas gut microbiota from CRC patients failed to do so. By 16S rRNA gene sequencing, we identified that was significantly increased in the mice with good response to anti-PD-1, and significantly correlated with anti-tumor immunity. After a series of screening, we isolated a novel strain, named showed the most notable anti-tumor immunity in the mice with gut dysbiosis. Mechanistically, the antitumor immune response elicited by was dependent on CD8 T cell. and studies revealed that stimulation triggered the upregulated expression of CXCL10 in the tumors and subsequently enhanced CD8 T cell recruitment. Meanwhile, the modulation of gut microbiota caused by enhanced its antitumor effect and gut barrier function. Overall, our study offered novel insights into the mechanism by which gut microbiota shaped the outcome of cancer immunotherapy and, more importantly, the novel strain might serve as an easy and effective way to promote anti-PD-1 effect in clinical practice.