Clinical and molecular mechanisms for predicting the efficacy of immunotherapy for hepatocellular carcinoma based on gut microbiome.

e16222 Background: Hepatocellular carcinoma (HCC) is an aggressive malignant tumor, ranking as the fifth most common cancer and the third leading cause of cancer-related deaths globally, posing a significant global health issue. Increasing evidence suggests that the gut microbiome and their metabolites play a crucial role in the development and therapeutic processes of cancer. Immune checkpoint inhibitors (ICIs) have recently become a treatment option for unresectable advanced HCC. To further guide the selection of immunotherapy for clinical HCC patients, it is necessary to further elucidate the prediction of immunotherapy efficacy for HCC based on the microbiome. Methods: The study enrolled 26 unresectable advanced HCC patients and collected baseline clinical laboratory data. We administered ICIs therapy to HCC patients every three weeks. After 6 months of treatment, patients were divided the responsive group (R group) and the non-responsive group (NR group) based on imaging evaluation according to the Response Evaluation Criteria in Solid Tumors (RECIST 1.1). Prior to the application of anti-tumor treatment, fecal samples were collected from the patients for 16S rRNA microbiome sequencing analysis. Immunofluorescence was used to detect the expression of PD-L1 in tumor tissue, and immunohistochemistry was used to assess changes in lymphocyte subsets CD3+T cells, CD4+T cells, CD8+T cells and Treg cells, as well as the expression of TNF-α, γ-IFN, and GZMB. Additionally, the peripheral blood lymphocyte subsets CD3+T cells, CD4+T cells and CD8+T cells were analyzed by flow cytometry. Results: In our study, R group showed higher taxa richness and more gene counts than those of NR group. Comparing with NR group, the relative abundance of Firmicutes were significantly increased, whereas Proteobacteria and Bacteroidota were significantly decreased in R group at phylum level (all P < 0.05). Our study showed that R group had high level of lymphocyte subsets CD3+T cells and CD8+T cells and low level of CD4+T cells and Treg cells compared to NR group (all P < 0.05). And the expressions of PD-L1, TNF-α,γ-IFN and GZMB were upregulated in R group(all P < 0.05). Conclusions: These findings suggested that the characteristics of gut-microbial diversity and composition at the early treatment period of ICIs therapy in HCC may have distinct implications on drug efficacy and disease prognosis. ICIs therapy reshaped HCC tumor microenvironment in parallel with regulating the gut microbiome and lymphocyte subsets immunity.