Introduction: Gut microbiota is an emerging factor for the response to immune checkpoint blockade (ICB) immunotherapy in multiple cancers. However, we currently lack a clear understanding of the interaction between gut microbiota and cancer cells. More importantly, we still ignore if targeting the gut microbes is sufficient to impact tumor growth. Our objectives were to first assess the modulatory effect of promising prebiotics on gut microbiota and on promoting antitumor response in bladder cancer (BCa), and to test the effects of prebiotics on the systemic antitumor efficacy of ICB immunotherapy.

Methods: C3H syngeneic male mice were injected subcutaneously with MBT-2 mouse bladder tumor cells. Prebiotics and control water were daily gavaged until the end of the experiment. Following tumor implantation, mice were treated with four injections of anti-PD1 monoclonal antibody or isotype control intraperitoneally. Tumor growth was monitored twice a week. Fecal samples were collected at many timepoints during tumor growth for the profiling of gut microbiota. Endpoint tumors were dissociated for flow cytometry analysis of tumor-infiltrating lymphocyte composition.

Results: Independently of immunotherapy, two prebiotics induced a significant reduction of tumor growth in comparison to the control group, and improved the overall survival of mice. Interestingly, one prebiotic combined with anti-PD1 immunotherapy also enhanced the systemic antitumor effect of ICB. Interactions between prebiotics and gut microbiota will be identified by 16S rRNA sequencing analysis while underlying mechanisms linking prebiotics treatment with tumor reduction will be deciphered by the flow cytometry analysis.

Conclusions: Overall, our findings support that promising prebiotics can induce an antitumor effect at steady state, and in combination with anti-PD-1 treatment, in BCa mouse model. These data will have a significant impact to enhance the clinical response to ICB treatment for BCa patients.