Hepatocellular carcinoma (HCC) is the most common liver primary cancer with a high rate of mortality. Since the results of IMbrave150, immunotherapy have emerged as a standard of care for HCC patients advanced and/or unresectable in first line of treatment. The objective response rate was about 30%, but half of patients would present only stable disease and about 20% progressive disease. Faecalibacterium prausnitzii is one of the most abundant bacterial in human gut microbiota, around 5% of total bacteria in feces. For patients with metastatic melanoma, treated with ipilimumab, an antibody targeting CTLA-4 (Cytotoxic T-lymphocyte-associated antigen 4), patients with a baseline gut microbiota enriched with Faecalibacterium had a significantly better clinical outcomes. In patients with metastatic melanoma, the level of Faecalibacterium prausnitzi at baseline was predictive of response to anti-PD-1 (programmed death-1) or anti-CTLA-4 therapy. EXL01 is a pharmacological preparation of Faecalibacterium prausnitzii strains. Preclinical murine study suggests that the administration of EXL01 could reverse the resistance to ICI induced by antibiotics (unpublished data). We thus plan to test the concept of microbiota modification in patients treated with standard-of-care approved first-line immunotherapy for advanced HCC. We would include patients refractory to first-line treatment, and test the addition of EXL01 to standard-of-care approved first-line immunotherapy in order to reverse resistance.