Modulating Bacteroides to boost anti-PD-1 immunotherapy in HCC.

Bacteroides-enriched gut microbiota derived from anti-PD-1-responsive patients with HCC significantly suppressed tumor growth in murine HCC models.

• Human fecal microbiota transplant (FMT) from anti-PD-1-responsive HCC patients was used to demonstrate this effect.
• The association between gut microbiota composition and anti-PD-1 immunotherapeutic efficacy was first observed in patients with HCC before being validated in murine models.
• Multiple clinically relevant murine HCC models were used to characterize tumor-associated microbial signatures using 16S ribosomal RNA gene sequencing.

ABX-3 administration selectively enriched Bacteroides within the gut microbial community and attenuated tumor initiation and progression in murine HCC models.

• ABX-3 was described as a non-hepatotoxic antibiotic cocktail, distinguishing it from other antibiotic regimens.
• ABX-3 was implemented as both a preventive and therapeutic intervention against HCC tumor initiation and progression.
• The selective enrichment of Bacteroides was identified as the mechanism by which ABX-3 exerted its antitumor effects.

ABX-3 enhanced the capacity of tumor antigen-specific T-cell receptor-I T cells to mount robust immune responses, culminating in targeted tumor regression following antigen-specific immunization.

• Functional validation experiments were performed to confirm the immune-enhancing effects of ABX-3.
• The enhancement of antigen-specific T-cell responses was linked to the Bacteroides enrichment caused by ABX-3.
• Tumor regression was demonstrated following antigen-specific immunization in the context of ABX-3-modulated microbiota.

Bacteroides thetaiotaomicron (B.th) was identified as a critical mediator that potentiated anti-PD-1 immunotherapy in HCC by relieving KLF2-dependent suppression in dendritic cells.

• B.th repopulation was studied following gut sterilization with ABX-5, allowing controlled assessment of B.th's specific contributions.
• Single-cell RNA sequencing of hepatic non-parenchymal cells was used to elucidate the immune mechanisms downstream of B.th.
• KLF2 (Krüppel-like factor 2) was identified as a suppressive factor in dendritic cells that B.th relieves.
• Among multiple Bacteroides species examined, B.th emerged as the critical mediator of immunotherapy potentiation.

The KLF2-TLR9 signaling axis in dendritic cells governed the activation of antigen-specific CD8+ T cells, thereby amplifying antitumor immunity within the HCC microenvironment.

• KLF2-toll-like receptor 9 (TLR9) signaling was identified as the mechanistic pathway linking B.th to enhanced antitumor immunity.
• Dendritic cell reprogramming through the KLF2/TLR9 pathway was the downstream mechanism by which B.th enhanced anti-PD-1 efficacy.
• Activation of antigen-specific CD8+ T cells was identified as the effector immune mechanism amplified by this signaling axis.
• This mechanism was elucidated using single-cell RNA sequencing of hepatic non-parenchymal cells together with functional validation experiments.