Bacteroidetes promote hepatocellular carcinoma progression and resistance to immunotherapy

Background and Aims: Growing evidence highlights the gut microbiome’s critical role in tumorigenesis and immunotherapy response. However, the impact of gut microbes on hepatocellular carcinoma (HCC) progression and response to immune checkpoint blockade (ICB) remains unclear due to the lack of combined preclinical and clinical studies. Approach and Results: We performed 16S rRNA sequencing of cross-cohort stool samples from 10 HCC responders (R) and 40 non-responders (NR) to ICB at baseline and on-treatment time points. We identified Bacteroidetes enrichment in NR. To study the microbiome’s role in cancer immune response, we generated an immunogenic mouse model of HCC via hydrodynamic tail-vein injection (HDTVI) of DNA plasmids mimicking common HCC alterations and immunogenicity by expressing OVA model antigens ( MYC-lucOS;CTNNB1 tumors). We found that antibiotic (ABX)-induced dysbiosis promoted a pro-tumorigenic effect in the MYC-lucOS;CTNNB1 HCC and reshaped the tumor immune microenvironment by reducing dendritic cells (DCs) through the expansion of the Bacteroidetes species, Parabacteroides distasonis . P. distasonis colonization in mice harboring MYC-lucOS;CTNNB1 liver tumors confirmed its pro-tumorigenic effect in vivo. Furthermore, fecal matter transplant of patient microbiotas into murine recipients demonstrated that microbiota from an NR donor enriched in Bacteroidetes promoted faster tumorigenesis compared with microbiota from an R donor with reduced Bacteroidetes . We isolated 6 Bacteroidetes species from the NR donor into a bacterial cocktail. After colonization with the Bacteroidetes cocktail, mice harboring MYC-lucOS;CTNNB1 HCC exhibited increased tumorigenesis, reduced survival, and impaired response to ICB. Conclusions: This study identified Bacteroidetes enrichment as a potential biomarker of ICB resistance in HCC and, by using immunogenic mouse models, established that Bacteroidetes abundance influences tumor development and response to ICB.