Immune microenvironment in hepatocellular carcinoma: from pathogenesis to immunotherapy

Abstract

Hepatocellular carcinoma (HCC) is an increasingly prevalent and deadly disease that is initiated by different etiological factors, such as alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatohepatitis (MASH), viral hepatitis, and other hepatotoxic and hepatocarcinogenic agents. The tumor microenvironment (TME) of HCC is characterized by several different fibroblastic and immune cell types, all of which affect the initiation, progression and metastasis of this malignant cancer. This complex immune TME can be divided into an innate component that includes macrophages, neutrophils, dendritic cells, myeloid-derived suppressor cells, mucosal-associated invariant T cells, natural killer cells, natural killer T cells, and innate lymphoid cells, as well as an adaptive component that includes CD4⁺ T cells, CD8⁺ T cells, regulatory T cells, and B cells. In this review, we discuss the latest findings shedding light on the direct or indirect roles of these immune cells (and fibroblastic-like cells such as hepatic stellate cells) in the pathogenesis of HCC. Henceforth, further characterization of this heterogeneous TME is highly important for studying the progression of HCC and developing novel immunotherapeutic treatment options. In line with this, we also review novel groundbreaking experimental techniques and animal models aimed at specifically elucidating this complex TME and discuss emerging immune-based therapeutic strategies intended to treat HCC and predict the efficacy of these immunotherapies.

Keywords: Hepatocellular carcinoma; Immune microenvironment; Immunotherapy..

Fig. 1

Impact of myeloid cell-mediated immunosuppression and cytotoxic T-cell exhaustion within the hepatocellular carcinoma immune microenvironment. One of the prominent members of the immune TME is myeloid cells, which mainly consist of TAMs derived from resident KCs or infiltrating MNMs through the action of various novel molecules and cytokines. TAMs secrete a wide variety of proinflammatory cytokines, such as IL-1β, IL-6 and TNF-α, that are involved in the initiation and progression of HCC. TAMs also act on all steps of HCC growth via various newly discovered mediators and molecules. TANs constitute another major type of myeloid cell that is commonly observed in the HCC TME and is differentiated from neutrophils through various chemokines. TANs also produce proinflammatory cytokines such as TNF-α and secrete NETs that favor HCC growth. In addition to TAMs and TANs, macrophages and neutrophils can also differentiate into M-MDSCs and PMN-MDSCs, respectively, which also play tumor-promoting and immunosuppressive roles within the TME. Owing to their inherent cytotoxic and antitumor role, CTLs are prone to inhibition and exhaustion mediated by the surrounding TME through various complex and heterogeneous mechanisms, ranging from extracellular molecules to interactions with other immune cell types. TME tumor microenvironment, HCC hepatocellular carcinoma, TAMs tumor-associated macrophages, MNMs monocyte-derived macrophages, KCs Kupffer cells, CTLs cytotoxic T lymphocytes, M-MDSCs monocytic myeloid-derived suppressor cells, PMN-MDSCs polymorphonuclear myeloid-derived suppressor cells, NK natural killer, TANs tumor-associated neutrophils, NETs neutrophil extracellular traps, IL interleukin, TNF tumor necrosis factor, TLR toll-like receptor, ROS reactive oxygen species, NO nitric oxide, VEGF vascular endothelial growth factor, TGF transformant growth factor, CCL C-C motif ligand, CTLA cytotoxic T lymphocyte-derived suppressor protein, T_regs regulatory T cells, MPO myeloperoxidase, TIM = T-cell immunoglobulin, LAG lymphocyte activation gene, PD-1 programmed cell death, PD-L1 programmed cell death ligand, 3-HAA = 3-hydroxyanthralinic acid, FGF fibroblast growth factor, CXCL C-X-C motif ligand, TMEM transmembrane protein, GM-CSF granulocyte‒macrophage colony-stimulating factor, GSDME gasdermin E, iNOS inducible nitric oxide synthase, Notch neurogenic locus notch homolog protein, ICAM intercellular adhesion molecule

Fig. 2

Activating and inhibitory effects of other innate and adaptive immune cell types within the hepatocellular carcinoma microenvironment. In contrast to cDCs and mregDCs, anti-inflammatory pDCs can result in the exhaustion phenotype of CTLs through various mechanisms. PMN-MDSCs and T_regs also have direct inhibitory effects on the cytotoxic function of CTLs. T_H17 cells, M-MDSCs and MAIT cells are also indirectly involved in the dysfunction phenotype of CTLs. NK cells are known antitumor protagonists through their cytotoxic activity; hence, HCC-ME inhibits the cytotoxic properties of NK cells. NKT cells are another type of lymphoid cell that exhibit antitumor functions. TME tumor microenvironment, HCC hepatocellular carcinoma, CTLs cytotoxic T lymphocytes, cDCs conventional dendritic cells, pDCs plasmacytoid dendritic cells, mregDCs mature DCs enriched in immunoregulatory molecules, M-MDSCs monocytic myeloid-derived suppressor cells, PMN-MDSCs polymorphonuclear myeloid-derived suppressor cells, NK natural killer, NKT cells natural killer T, MAIT mucosal-associated invariant T, IL interleukin, TGF transformant growth factor, IFN-γ interferon-γ, TNF tumor necrosis factor, TNFR TNF receptor, HSCs hepatic stellate cells, IRF interferon regulatory factor, NR4A1 nuclear stellate cells-4A1, TM4SF1 transmembrane-4 L six family member-1, TDEs tumor-derived exosomes, circUHRF1 circular ubiquitin-like with PHD and ring finger domain-1, CXCL C-X-C motif ligand, cGAS cyclic GMP-AMP, STING stimulator of interferon genes, TCR T-cell receptor, ARG arginase, ROS reactive oxygen species

Fig. 3

Experimental animal models used to study the impact of the immune-related HCC microenvironment. Genetically engineered/transgenic mice: Created via Cre-LoxP or CRISPR-Cas9 to overexpress or knock out oncogenes in hepatocytes, enabling studies of gene function and tumor-immune interactions. Chemically induced models: Tumors are initiated via the use of genotoxic (e.g., DEN) or nongenotoxic agents that mimic chronic liver injury, inflammation, and fibrosis. Patient-derived xenograft (PDX) mice: Human HCC tissues are implanted into immunodeficient mice, preserving tumor heterogeneity. Syngeneic mice: Mouse HCC cells are transplanted into genetically identical mice, allowing immune-competent tumor studies. Dietary models: Diets such as Western, alcohol, or high-fiber diets induce liver conditions that drive or modulate HCC development

Fig. 4

Barcelona Clinic Liver Cancer (BCLC) staging system and corresponding treatment strategies for hepatocellular carcinoma (HCC). This figure illustrates treatment allocation according to tumor burden, liver function (Child‒Pugh classification), and performance status (ECOG: Eastern Cooperative Oncology Group). Curative approaches—including liver resection, ablation, and transplantation—are recommended for early-stage disease (BCLC 0–A). Intermediate-stage HCC (BCLC B) is typically managed with transarterial therapies; however, systemic therapy may also be considered a first-line option in selected patients with high tumor burdens or who are unsuitable for transarterial therapies. Advanced-stage disease (BCLC-C) is treated with systemic agents, including immunotherapy-based regimens such as atezolizumab–bevacizumab, durvalumab–tremelimumab, and nivolumab–ipilimumab. End-stage disease (BCLC D) is managed with best supportive care. Treatment goals vary by stage and include curative intent, disease control, downstaging, or symptom management. Notably, the integration of immune checkpoint inhibitors with locoregional therapies such as TACE is an emerging strategy under active investigation, particularly in intermediate-stage HCC, and may further refine future therapeutic algorithms