How the gut microbiome affects the immunotherapy response in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) remains a major global health challenge with limited long-term survival despite advances in surgical, locoregional, and systemic treatments. Although immune checkpoint blockade (ICB) has reshaped HCC therapy, only a subset of patients achieves durable responses, reflecting substantial heterogeneity in tumor biology and immune microenvironments. Dysbiosis, involving the loss of beneficial bacteria, like Lactobacillus reuteri and Akkermansia muciniphila, and the expansion of pathogens, such as Klebsiella pneumoniae and Catenibacterium mitsuokai, drives HCC by promoting microbial translocation and chronic inflammation. This process is mediated by microbiota-derived metabolites. Pro-carcinogenic agents, like deoxycholic acid (DCA) and quinolinic acid, induce inflammation and activate oncogenic pathways, while protective short-chain fatty acids (SCFAs), like acetate and butyrate, modulate T-cell and ILC3 responses to influence antitumor immunity. Tryptophan catabolites, acting via the aryl hydrocarbon receptor (AhR), further fine tune immune and barrier functions. In addition, emerging data implicate intratumoral microbiota as active modulators of immune suppression and metastatic behavior. These mechanistic insights have accelerated the development of microbiome-targeted interventions, such as probiotics, prebiotics, engineered bacterial strains, and fecal microbiota transplantation, to enhance ICB responsiveness. This review synthesizes current advances linking the gut microbiome to HCC immunobiology and highlights emerging therapeutic strategies aimed at optimizing immunotherapy through precise microbial modulation.