The scope of therapeutic options for the treatment of hepatocellular carcinoma (HCC) has recently been expanded by immunotherapeutic regimens. T cell-based therapies, especially in combination with other treatments have achieved far better outcomes compared to conventional treatments alone. However, there is an emerging body of evidence that eliciting T cell responses in immunotherapeutic approaches is insufficient for favorable outcomes. Immune responses in HCC are frequently attenuated in the tumor microenvironment (TME) or may even support tumor progress. Hence, therapies with immune checkpoint inhibitors or adoptive cell therapies appear to necessitate additional modification of the TME to unlock their full potential. In this review, we focus on immunotherapeutic strategies, underlying molecular mechanisms of CD8 T cell immunity, and causes of treatment failure in HCC of viral and non-viral origin. Furthermore, we provide an overview of TME features in underlying etiologies of HCC patients that mediate therapy resistance to checkpoint inhibition and discuss strategies from the literature concerning current approaches to these challenges.

Background and Aims: The risk of developing HCC in chronically infected patients with AQ2 HCV with liver cirrhosis is significantly elevated. This risk remains high even after a sustained virological response with direct-acting antivirals. To date, disease-associated signatures of NK cells indicating HCC development are unclear. Approach and Results: This study investigated NK cell signatures and functions in 8 cohorts covering the time span of HCC development, diagnosis, and onset. In-depth analysis of NK cell profiles from patients with cirrhosis who developed HCC (HCV-HCC) after sustained virological response compared with those who remained tumor-free (HCV-noHCC) revealed increasingly dissimilar NK cell signatures over time. We identified expression patterns with persistently high frequencies of TIM-3 and CD38 on NK cells that were largely absent in healthy controls and were associated with a high probability of HCC development. Functional assays revealed that the NK cells had potent cytotoxic features. In contrast to HCV-HCC, the signature of HCV-noHCC converged with the signature found in healthy controls over time. Regarding tissue distribution, single-cell sequencing showed high frequencies of these cells in liver tissue and the invasive margin but markedly lower frequencies in tumors Conclusions: We show that HCV-related HCC development has profound effects on the imprint of NK cells. Persistent co-expression of TIM-3hi and CD38⁺ on NK cells is an early indicator for HCV-related HCC development. We propose that the profiling of NK cells may be a rapid and valuable tool to assess the risk of HCC development in a timely manner in patients with cirrhosis after HCV cure.

Background and Aims: Bulevirtide (BLV) is a novel and the only approved treatment option for patients with chronic hepatitis D (CHD). BLV alleviates liver inflammation early during treatment when only minor HDV RNA changes are observed. We hypothesized that BLV treatment may influence immune cells in patients with CHD and performed a high-resolution analysis of natural killer (NK) cells before and during BLV therapy. Approach and Results: BLV-treated patients with CHD (n=20) from a single-center cohort were longitudinally analyzed for clinical, molecular, and virological parameters. Peripheral blood mononuclear cells were studied at baseline, and therapy weeks 3 and 48 by spectral flow cytometry. Healthy donors, patients with chronic hepatitis C after direct-acting antiviral treatment, and patients with chronic hepatitis B were used as controls. Overall, NK cell frequencies remained stable during BLV treatment. However, biochemical responders showed distinct NK cell immunophenotypic features before and during therapy. TIGIT expression increased on CD56 ^dim and CD56 ^bright NK cells during the course of BLV treatment and inversely correlated with ALT levels in CHD but not patients with CHC or CHB. High frequencies of TIGIT ⁻ CD57 ⁺ CD56 ^dim NK cells at baseline and low levels during therapy were indicative of a biochemical response. Conclusions: We here suggest that lacking the expression of the immune checkpoint inhibitor TIGIT on NK cell subtypes may be a hallmark of liver inflammation in HDV infection. BLV therapy is associated with a reappearance of TIGIT on these cells, which may be one mechanism of why liver enzymes rapidly improve during therapy.