Lacticaseibacillus paracasei sh2020 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 Lactobacillus 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 Lacticaseibacillus strain, named L. paracasei sh2020. L. paracasei sh2020 showed the most notable anti-tumor immunity in the mice with gut dysbiosis. Mechanistically, the antitumor immune response elicited by L. paracasei sh2020 was dependent on CD8(+) T cell. In vitro and in vivo studies revealed that L. paracasei sh2020 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 L. paracasei sh2020 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 L. paracasei sh2020 might serve as an easy and effective way to promote anti-PD-1 effect in clinical practice.

Automated summary

The gut microbiota plays a critical role in cancer immunotherapy outcomes. The study found that the gut microbiota from healthy individuals enhances sensitivity to anti-PD-1 in colorectal cancer tumor-bearing mice, while gut microbiota from CRC patients does not have the same effect. Lactobacillus was identified as a key species significantly increased in mice with a good response to anti-PD-1, and it was correlated with anti-tumor immunity. The novel strain L. paracasei sh2020 demonstrated notable anti-tumor immunity and enhanced gut barrier function, suggesting its potential as an effective way to promote the effect of anti-PD-1 in clinical practice.