Immunotherapy in hepatocellular carcinoma: translating mechanistic insights into clinical advances

Abstract

Hepatocellular carcinoma is the most common primary liver cancer and a leading cause of cancer-related mortality worldwide. Traditional systemic therapies, such as tyrosine kinase inhibitors, offer limited survival benefits, prompting the emergence of immunotherapy as a transformative approach. This review synthesizes mechanistic insights into the tumor microenvironment of hepatocellular carcinoma with clinical evidence from pivotal trials on immune checkpoint inhibitors. It summarizes outcomes from monotherapy and combination regimens incorporating antiangiogenic agents, tyrosine kinase inhibitors, radiotherapy, and locoregional therapies like transarterial chemoembolization or hepatic arterial infusion chemotherapy. Emerging modalities, including therapeutic vaccines, oncolytic viruses, Toll-like receptor agonists, and adoptive cell therapies, are also examined. Immune checkpoint inhibitors targeting programmed cell death protein 1, its ligand, and cytotoxic T-lymphocyte-associated protein 4 elicit durable responses in subsets of patients, though monotherapy provides modest overall benefits. Combination strategies, such as atezolizumab plus bevacizumab, tremelimumab–durvalumab (STRIDE), and nivolumab plus ipilimumab (CheckMate-9DW), have set new standards of care by significantly extending overall survival with acceptable toxicity. Resistance mechanisms involve tumor-intrinsic factors like beta-catenin signaling and antigen presentation defects, alongside microenvironmental elements including regulatory T cells, myeloid-derived suppressor cells, and cytokine networks. Effective management of immune-related adverse events, particularly hepatic toxicities, is critical. Immunotherapy has revolutionized hepatocellular carcinoma treatment, fostering multimodal and personalized strategies. Future directions emphasize validated biomarkers, optimized sequencing, and randomized trials to broaden long-term survival gains.

Introduction

HCC represents the leading primary cancer of the liver and represents a significant global health burden [1]. According to recent global cancer statistics, liver cancer ranks as the sixth most frequently diagnosed cancer and the third leading cause of cancer-related mortality, accounting for approximately 830,000 deaths annually [2]. The incidence of HCC is highest in regions with endemic hepatitis B and C virus infections, including East and Southeast Asia, Sub-Saharan Africa, and parts of the Middle East [3].

The development of HCC is strongly linked to chronic liver disease and cirrhosis [4]. Major risk factors include chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, alcohol-related liver disease, and non-alcoholic fatty liver disease (NAFLD), all of which drive persistent hepatic inflammation, fibrosis, and genomic alterations [5]. For example, hepatitis B virus (HBV) promotes hepatocarcinogenesis via viral DNA integration, genomic instability, and oncogenic proteins (e.g., HBx) that perturb cellular signaling [6].

Diagnosis of HCC can be achieved through both invasive and non-invasive approaches [7]. While liver biopsy provides histological confirmation, it is not routinely required in all cases due to advances in imaging and biomarker-based methods [8]. Non-invasive diagnostic strategies include serological biomarkers such as alpha-fetoprotein (AFP), AFP-L3, and des-gamma-carboxy prothrombin (DCP), which can aid in early detection and disease monitoring [9]. In addition, multiphasic contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) are critical imaging modalities that provide high sensitivity and specificity for the diagnosis of HCC based on characteristic vascular patterns [10].

Managing HCC is challenging due to late diagnosis, coexisting liver disease that limits treatment options, high recurrence rates, and intrinsic tumor resistance [11]. Despite considerable advances in therapeutic strategies, a significant obstacle remains that HCC is often diagnosed at advanced stages, when potentially curative interventions such as surgical resection or liver transplantation are no longer feasible, making systemic therapy the cornerstone of management [12, 13].

Sorafenib and lenvatinib, both tyrosine kinase inhibitors (TKIs), have historically been applied as frontline systemic therapies for advanced HCC [14]. In cases of disease progression or inadequate response, agents such as cabozantinib and ramucirumab are administered to disrupt angiogenesis and slow down tumor expansion. However, the clinical benefits of these therapies are generally modest, underscoring the need for more effective treatment modalities [15].

In recent years, immunotherapy has emerged as a promising strategy for HCC, aiming to enhance the host immune response against tumor cells [16, 17]. Immunotherapeutic approaches include cancer vaccines, monoclonal antibodies (mAbs), adoptive cellular therapies such as CAR-T cells, and immune checkpoint inhibitor (ICI) treatment [18, 19]. Among these, ICIs have shown transformative potential, with agents such as atezolizumab (anti–PD-L1), nivolumab (anti–PD-1), and pembrolizumab (anti–PD-1) restoring antitumor T-cell activity suppressed by the immunosuppressive tumor microenvironment (TME) [20, 21].

A major challenge in HCC immunotherapy arises from the liver’s inherently immunosuppressive environment, which naturally inhibits immune activation and may reduce ICI efficacy [22, 23]. Moreover, tumor responses to ICIs are highly variable, reflecting differences in the TME across liver regions and their modulation by factors such as localized inflammation, fibrosis, and angiogenesis [24]. These complexities highlight the urgent need for a deeper understanding of immune evasion and resistance mechanisms in HCC.

This review focuses on the clinical application of ICIs in HCC, with particular emphasis on combination therapies, their efficacy, associated adverse events, and evidence-based strategies to mitigate toxicity.

TME and immune regulation in HCC

The TME in HCC is dynamic and multilayered and promotes tumor growth, invasion, metastasis, and therapy resistance [25]. Chronic liver inflammation caused by HBV, HCV, and NAFLD contributes to TME formation through fibrosis and immune dysregulation [26]. This environment consists of malignant cells, cancer-associated fibroblasts (CAFs), hepatic stellate cells (HSCs), immune cells, extracellular matrix (ECM), and a wide range of signaling molecules that collectively sustain tumor progression [27, 28].

Within the TME, immune populations are generally categorized into inhibitory and tumor-fighting groups [29]. The inhibitory arm consists of tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), myeloid-derived suppressor cells (MDSCs), and regulatory T cells (Tregs), all of which weaken antitumor responses. Conversely, cytotoxic T lymphocytes (CTLs), natural killer (NK) cells, dendritic cells (DCs), and Th1 helper cells form the pro-immune, tumor-attacking subset, though their function is frequently compromised by the surrounding immunosuppressive conditions [30].

CAFs, often derived from HSCs, remodel the extracellular matrix (ECM), increasing its density and rigidity. This creates a physical barrier to immune-cell infiltration and promotes growth-factor sequestration. CAFs also recruit Th1 cells through CXCL11 secretion and promote migration and metastasis via CXCL12–CXCR4 interactions [31, 32]. CAFs also secrete IL-6, which can activate NOTCH signaling and induce stem-like phenotypes in HCC cells, thereby promoting proliferation, invasion, and therapy resistance [33, 34]. In addition, CAFs facilitate immune escape by reducing NK cell function via the release of IDO and PGE2 [35].

Various signaling cascades and cell-to-cell interactions contribute to the recruitment of immune cells into the TME. TAMs are recruited by dominant tumor- and stroma-derived cues, most notably TGF-β and VEGF, together with colony-stimulating signals (e.g., M-CSF) and CXC chemokine gradients (e.g., the CXCL family) [36]. TAMs suppress immune responses and promote tumor progression through the secretion of anti-inflammatory cytokines, notably IL-10 and TGF-β [37]. They also contribute to angiogenesis and nutrient supply within the TME by releasing VEGF and platelet-derived growth factor (PDGF) [38]. Furthermore, TAMs facilitate metastasis in HCC by stimulating the epithelial–mesenchymal transition (EMT) pathway and inducing aggressive traits [39].

Tregs are recruited to the TME under the influence of tumor-derived VEGF. Tregs inhibit CD8⁺ T cells by secreting interleukin-35 (IL-35) and expressing forkhead box protein P3 (FoxP3), resulting in diminished cytotoxic activity and induction of T cell exhaustion. Exhaustion in CD8⁺ T cells is characterized by the expression of PD-1, along with increased expression of inhibitory receptors such as T cell immunoglobulin and mucin-domain containing-3 (TIM-3) and CTLA-4. In this state, CD8⁺ T cells also secrete interleukin-10 (IL-10), further impairing antitumor immunity [40, 41].

Cytokines like CXCL6 and TGF-β, released by CAFs, drive the recruitment of tumor-associated neutrophils (TANs) into the tumor microenvironment [42]. TANs, which predominantly display the N2 phenotype, function as immunosuppressive cells and promote tumor progression and metastasis [42]. TANs contribute to extracellular matrix degradation by secreting matrix-degrading proteases (e.g., MMP-9). Additionally, the formation of neutrophil extracellular traps (NETs) by TANs facilitates HCC metastasis [43]. Moreover, the expression of PD-L1 by TANs suppresses T cell activity, thereby further weakening antitumor immune responses [44].

Beyond Tregs, MDSCs represent another key immunosuppressive component within the HCC TME. These cells induce T-cell apoptosis and inhibit T-cell proliferation, thereby suppressing antitumor immunity [45]. Studies indicate that elimination of MDSCs enhances the effectiveness of sorafenib and improves the response to immunotherapy [46]. A disturbance in DCs reflects a malfunction in antigen presentation. Chronic inflammation can polarize dendritic cells toward a tolerogenic phenotype, reducing antigen presentation and impairing adaptive immune responses [47, 48]. Chronic inflammation results in a scenario where DCs inhibit the immune system rather than activate it. Furthermore, NK cells show reduced cytotoxic activity as a result of heightened inhibitory receptor expression and diminished NKG2D levels, impairing their capacity to detect and destroy tumor cells [49, 50].

Immunotherapeutic strategies for HCC

HCC remains a highly lethal malignancy, mainly due to late diagnosis, absence of reliable screening, coexisting liver disease that restricts therapeutic options, pronounced genomic heterogeneity driving resistance, and an immunosuppressive TME that impairs antitumor immunity [1, 51]. Current therapeutic strategies include surgical resection, liver transplantation, local ablation techniques such as radiofrequency (RFA) and microwave ablation (MWA), and intra-arterial approaches including transarterial chemoembolization (TACE) [52, 53]. While these interventions can be curative in selected patients, their applicability is limited, and recurrence rates remain high.

In this setting, immunotherapy has gained attention as a potential strategy to boost immune recognition and clearance of cancerous hepatocytes [17, 54]. Several methods are currently under investigation. Cancer vaccines aim to elicit tumor-specific T-cell responses, adoptive cell therapies, including cytokine-induced killer (CIK) cells and chimeric antigen receptor T (CAR-T) cells, enhance targeted cytotoxicity, and oncolytic virotherapy employs engineered viruses to lyse tumor cells while stimulating antitumor immunity [55] Additional approaches include cytokine-based therapies, such as interferon-alpha, and Toll-like receptor (TLR) agonists that activate innate immunity and promote dendritic cell priming [56].

Clinical translation of these strategies has yielded mixed outcomes. Therapeutic cancer vaccines have demonstrated limited efficacy as monotherapy in HCC, with most contemporary studies focusing on combination regimens with immune checkpoint inhibitors [57]. A representative example is the phase I/II HepaVac-101 trial, which evaluated a multi-epitope peptide vaccine (IMA970A) administered with an immunostimulatory adjuvant. Although antigen-specific T-cell responses were observed in a subset of patients, the vaccine did not significantly improve survival or achieve durable tumor control [58]. These findings suggest that vaccine monotherapy may be insufficient for long-term disease management but remains a valuable platform for combinatorial strategies.

Translationally, therapeutic vaccines in HCC face key barriers including antigen heterogeneity, immune tolerance in the cirrhotic liver, and limited T-cell trafficking into an immunosuppressive TME [57]. Consequently, vaccine monotherapy is unlikely to be practice-changing, and the most plausible clinical path is rational combinations (e.g., checkpoint blockade, anti-VEGF priming, or locoregional antigen release) with immune-monitoring to demonstrate on-target T-cell expansion and intratumoral infiltration [58, 59]. Future trials should prioritize standardized immunogenicity endpoints, biomarker-enriched designs, and clinically meaningful survival readouts beyond early ORR signals.

In adoptive cell therapy, the phase I C-CAR031 trial evaluated CAR-T cells directed against glypican-3 and modified with a dominant-negative TGF-β receptor II to counteract TGF-β–driven immunosuppression in the tumor microenvironment. Among patients with advanced, treatment-resistant HCC, preliminary findings showed reductions in tumor burden and durable responses in some individuals, with an acceptable safety profile [60].

For adoptive cell therapies, major translational hurdles include on-target/off-tumor toxicity risks, impaired trafficking and persistence in solid tumors, antigen escape, and safety constraints in patients with advanced cirrhosis [61, 62]. Manufacturing complexity, cost, and scalability further limit near-term applicability. Progress will likely depend on multi-antigen targeting, safety switches, strategies that remodel the TME (e.g., TGF-β resistance engineering), and careful patient selection in earlier-stage or downstaging settings [63].

Oncolytic virotherapy has also shown promise. The multicenter phase I VG161 trial investigated a modified herpes simplex virus type 1 engineered to express IL-12, IL-15 with its α-receptor, and a PD-1/PD-L1 inhibitor, administered through intratumoral or intrahepatic injection. VG161 induced significant immune cell infiltration, reprogrammed the TME, and achieved measurable tumor shrinkage in some patients, with predominantly low-grade, manageable adverse events [64]. This approach exemplifies a broader shift in cyt okine-based therapies from systemic administration of classical agents, such as interferon-alpha or interleukin-2, toward localized delivery via gene therapy or viral platforms, potentially improving tissue targeting while minimizing systemic toxicity.

Oncolytic viruses also face translational constraints, including delivery feasibility (intratumoral/intrahepatic access), pre-existing antiviral immunity, and safety monitoring in a virally infected or cirrhotic liver [65]. Signals of immune activation are encouraging, but durable benefit will require controlled studies clarifying optimal dosing, sequencing with ICIs/anti-VEGF therapy, and whether systemic (abscopal) immune effects can be consistently achieved [66, 67].

Similarly, preliminary studies of TLR agonists suggest promise. The phase Ib PERIO-02 trial investigated SD-101, a class C TLR9 agonist, administered via hepatic arterial infusion in HCC and cholangiocarcinoma. The therapy showed acceptable tolerability and enhanced intratumoral CD8 + T-cell infiltration in some patients, while survival outcomes are still pending [68].

While these approaches collectively expand the therapeutic landscape of HCC, the strongest clinical evidence for a durable survival benefit to date has come from immune checkpoint inhibitors, which restore T-cell function and counteract tumor-driven immunosuppression. Accordingly, the following sections of this review will provide an in-depth analysis of immune checkpoint inhibition as the cornerstone of modern HCC immunotherapy [69–71].

ICI therapy in HCC

ICIs are currently the most established form of immunotherapy in HCC. These agents work by blocking inhibitory receptors such as PD-1, its ligand PD-L1, and CTLA-4, thereby restoring T-cell function and reducing the effects of the immunosuppressive TME [72, 73]. Over the past decade, multiple landmark clinical trials have evaluated ICIs as monotherapy across different treatment settings, ranging from second-line use after tyrosine kinase inhibitors to first-line therapy in advanced or unresectable HCC [69, 74–76].

The results of these trials, summarized in Table 1, reveal consistent patterns. Single-agent ICIs can achieve durable and clinically meaningful responses in a subset of patients, demonstrating proof-of-concept for checkpoint blockade in HCC. However, overall response rates remain modest, and only a minority of unselected patients benefit [77, 78]. These findings highlight both the therapeutic potential and the limitations of monotherapy. Based on these observations, the following sections will examine PD-1/PD-L1 and CTLA-4 inhibitors in greater depth, focusing on their clinical outcomes, safety profiles, and their central role in combination strategies.

Table 1.

Summary of selected clinical trials investigating immune checkpoint inhibitor (ICI) monotherapy in patients with hepatocellular carcinoma (HCC)

NCT Number	Phase	Condition	Enrollment	Therapeutic Modality	Endpoints	Results
NCT01658878	I/II	Advanced HCC (± Sorafenib)	262	Nivolumab	ORR, OS, Safety	ORR: 14–20%; OS: 15.6 mo
NCT02702414	II	Advanced HCC after Sorafenib	104	Pembrolizumab	ORR (RECIST 1.1)	ORR: 17%; DOR: 16.4 mo
NCT03412773	III	Unresectable HCC (1st line)	674	Tislelizumab	OS, ORR	OS: 15.9 mo; non-inferior to sorafenib
NCT02989922	II	Advanced HCC (Chinese patients)	217	Camrelizumab	ORR, OS	ORR: 14.7%; OS: 13.8 mo
NCT02113657	I	Advanced solid tumors incl. HCC	90	Atezolizumab	Safety, ORR	ORR (HCC cohort): 13%; good tolerability
NCT01853618	I	Advanced HCC	40	Tremelimumab	DCR, TTP	DCR: 76%; TTP: 6.5 mo

The table presents key trials assessing single-agent PD-1, PD-L1, or CTLA-4 inhibitors. Endpoints include overall response rate (ORR), overall survival (OS), disease control rate (DCR), duration of response (DOR), progression-free survival (PFS), and time to progression (TTP). Reported findings reflect efficacy, safety, and clinical relevance in various HCC populations

PD-1/PD-L1 blockade in HCC

The PD-1 and its ligand PD-L1 represent the most extensively studied checkpoint pathway in HCC. Overexpression of PD-L1 in the TME and the accumulation of exhausted T cells are key features of HCC that enable immune evasion [79]. Monoclonal antibodies targeting this axis restore effector T-cell function and have produced durable responses in subsets of patients, establishing proof of concept for checkpoint blockade in liver cancer [80].

The phase I/II CheckMate-040 trial of nivolumab was the first to show apparent clinical efficacy in advanced HCC, including patients previously treated with sorafenib. Although only a minority responded, some patients had durable regressions and acceptable toxicity, prompting accelerated approval for second-line use [81]. In contrast, the phase III CheckMate-459 trial did not meet its primary endpoint versus sorafenib, despite a favorable survival trend [82]. These results underscored both the promise and the limits of PD-1 monotherapy.

Pembrolizumab showed similar outcomes. In the phase II KEYNOTE-224 trial, pembrolizumab achieved meaningful and durable responses in sorafenib-pretreated patients [83]. Yet, the larger phase III KEYNOTE-240 trial narrowly missed statistical significance for overall and progression-free survival, even though numerical improvements were observed [84]. Thus, while pembrolizumab can provide long-lasting benefit in a subset, its overall impact in unselected populations remains modest.

More recently, the global phase III RATIONALE-301 trial demonstrated that tislelizumab was non-inferior to sorafenib as first-line therapy for unresectable HCC [85]. This provided the first large-scale evidence supporting a PD-1 inhibitor as a frontline option, though durable benefit applied only to a proportion of patients. Camrelizumab has also shown encouraging efficacy with manageable toxicity in second-line settings, particularly in Chinese cohorts [86].

PD-L1 inhibitors have likewise been investigated. Atezolizumab monotherapy was tolerable and showed preliminary antitumor activity in early-phase studies. However, its most significant clinical impact has been achieved in combination regimens rather than as a single agent [87].

Taken together, these studies establish PD-1/PD-L1 blockade as a transformative approach in HCC, proving that durable immune-mediated tumor control is possible. Nonetheless, the modest overall benefit of monotherapy highlights the urgent need for predictive biomarkers and rational combinations to extend efficacy to a broader patient population.

CTLA-4 blockade in HCC

CTLA-4 was one of the earliest immune checkpoint pathways recognized as a therapeutic target in cancer [88]. It plays a pivotal role during the initial stage of T-cell activation in lymphoid organs by competing with CD28 for binding to B7 ligands on antigen-presenting cells, thereby reducing T-cell stimulation [89]. In HCC, this suppressive effect is intensified by the liver’s naturally tolerogenic immune setting, further weakening antitumor responses. Consequently, CTLA-4 inhibition has been explored to enhance T-cell activation and restore immune surveillance [23].

The earliest clinical evidence in this setting came from tremelimumab, a fully human monoclonal antibody targeting CTLA-4. In a phase II study enrolling patients with HCC and concomitant chronic hepatitis C infection, tremelimumab monotherapy achieved a high disease control rate and prolonged time to progression, while also leading to a notable reduction in viral load [90]. These findings provided not only proof-of-concept for CTLA-4 blockade in HCC but also highlighted its dual antitumor and antiviral activity. While CTLA-4 inhibitors show measurable antitumor activity as monotherapy, their most significant clinical impact has emerged in combination with other checkpoint inhibitors [91]. This combined approach helps overcome the limited benefit of single-agent CTLA-4 blockade. The main challenge remains balancing clinical efficacy with immune-related toxicities, and the mechanisms of resistance, along with safety considerations, are discussed in the following Sects [92–94].

Combination therapies

Despite impressive progress in immunotherapy, monotherapy with ICI has not led to a significant improvement in OS. This limitation highlights the necessity for combination therapies, which have been shown to enhance OS significantly, overall response rate (ORR) and disease control [95]. Combined immunotherapy is generally considered a more effective treatment approach than targeted monotherapy [96]. Recently, several ICI-based combination therapies have shown promising outcomes in patients with unresectable HCC.

ICIs and TKIs/Anti-VEGFs

An effective therapeutic strategy in HCC is the integration of PD-1/PD-L1 inhibitors with TKIs or anti-VEGF monoclonal antibodies. Anti-angiogenic therapies can normalize tumor vasculature and promote immune cell infiltration, thereby enhancing the activity of PD-1/PD-L1 blockade [97]. Agents in this class include ramucirumab, bevacizumab, and apatinib [98]. Approved TKIs such as sorafenib and lenvatinib are widely used as first-line treatments, while regorafenib and cabozantinib serve as second-line options. In addition, ramucirumab, a monoclonal antibody against VEGFR-2, has been approved for patients with serum alpha-fetoprotein (AFP) levels > 400 ng/mL after sorafenib therapy [99].

The phase III IMbrave150 trial showed that atezolizumab combined with bevacizumab significantly improved OS and progression-free survival (PFS) compared with sorafenib in unresectable HCC, establishing this regimen as a new standard of care [69]. Other pivotal trials have investigated similar strategies, including COSMIC-312 (cabozantinib + atezolizumab) and LEAP-002 (lenvatinib + pembrolizumab). Although some of these studies did not reach statistical significance for OS, improvements in PFS and objective tumor responses suggest meaningful clinical benefit. A phase Ib study of lenvatinib plus pembrolizumab also demonstrated promising antitumor activity with manageable toxicities and no unexpected safety concerns [75].

A recent meta-analysis and systematic review of five major phase III trials, IMbrave150, ORIENT-32, COSMIC-312, LEAP-002, and CARES-310, assessed the therapeutic impact and safety of combining PD-1/PD-L1 blockade with anti-angiogenic agents in unresectable HCC. The pooled analysis of 1,515 patients demonstrated a 29% reduction in mortality risk (HR = 0.71, 95% CI 0.58–0.88) and a consistent improvement in progression-free survival (PFS). The overall response rate (ORR) also increased significantly (RR = 1.27), albeit with a modest rise in treatment-related adverse events [100].

Interestingly, these regimens have shown particular effectiveness in hepatitis B virus (HBV)-related HCC, especially among Asian patients. In one study, lenvatinib or apatinib combined with anti-PD-1 antibodies (nivolumab, pembrolizumab, or sintilimab) enabled surgical resection in approximately 16% of advanced-stage patients (BCLC stage C, median tumor size > 9 cm) within 2.3 months of initiating therapy [101].

Additional evidence supports the combination of nivolumab with cabozantinib, where patients achieved higher ORR and disease control rate (DCR), along with reductions in tumor markers such as AFP, GP-73, and AFP-L3. Immunologically, treatment increased CD3 + and CD4 + T-cell levels, with a favorable CD4+/CD8 + balance, while maintaining an acceptable safety profile [102].

More recently, the CARES-310 international phase III trial compared camrelizumab (anti–PD-1) plus rivoceranib (a TKI) with sorafenib in 543 patients. The combination provided significant and clinically meaningful improvements in OS and PFS. The most common grade 3–4 treatment-related adverse events were hypertension, palmar–plantar erythrodysesthesia, and elevations in AST and ALT [103]. Overall, ICIs combined with TKIs/anti-VEGFs markedly increase survival outcomes compared with monotherapy, with side effects such as hypertension, proteinuria, diarrhea, and fatigue generally manageable through supportive care [104].

Anti-PD-1/PD-L1 + Anti-CTLA-4

An emerging treatment approach is the dual use of PD-1/PD-L1 inhibitors together with CTLA-4 blockade. This dual inhibition is hypothesized to exert synergistic effects by enhancing T-cell activation and alleviating tumor-mediated immunosuppression.

In the CheckMate-040 trial, nivolumab in combination with ipilimumab was evaluated in patients with advanced HCC who had either progressed on or were intolerant to sorafenib. Patients were randomized into three different dosing schedules, resulting in 7 complete responses and 39 partial responses among 148 evaluable patients. The safety profile was consistent with that observed in other malignancies, with grade 3–4 treatment-related adverse events (TRAEs) reported in 55 patients (37.7%) and treatment discontinuation in 13 patients (8.9%). Overall, the combination demonstrated manageable safety and encouraging clinical activity [76, 105].

The HIMALAYA trial investigated the STRIDE regimen, consisting of a single priming dose of tremelimumab (300 mg) plus durvalumab (1500 mg) on day 1, followed by durvalumab (1500 mg) every 4 weeks, compared with sorafenib. At five years post-treatment, 20% of patients receiving STRIDE remained alive versus only 9% in the sorafenib arm [106]. Updated analyses confirmed a sustained OS advantage with STRIDE, coupled with a manageable safety profile. Tumor shrinkage of any magnitude was associated with improved OS, with the greatest benefit observed in patients achieving deep responses. This regimen has since established a new benchmark for unresectable HCC, with approximately one in five patients achieving five-year survival, and has been FDA-approved [107].

The phase 3 CheckMate-9DW trial compared nivolumab plus ipilimumab with lenvatinib or sorafenib as first-line therapy in unresectable HCC. Although early mortality was slightly higher in the immunotherapy arm, long-term follow-up demonstrated a sustained survival benefit, consistent with the delayed activity of immuno-oncology agents. These results, in line with findings from CheckMate-040, supported the FDA approval of nivolumab plus ipilimumab in April 2025 [108].

In addition, cadonilimab, the first bi-specific antibody targeting both PD-1 and CTLA-4, has been evaluated in combination with lenvatinib as a first-line therapy for unresectable HCC. A retrospective analysis of 29 patients demonstrated superior efficacy compared to earlier combination regimens. Both the objective response rate (ORR) and median progression-free survival (mPFS) were significantly improved, while adverse events remained manageable. These findings highlight the potential of dual-targeting antibodies to achieve meaningful outcomes in real-world clinical settings [109].

Despite these promising results, immune-related adverse events (irAEs) remain a major concern. In the HIMALAYA trial, grade 3–4 irAEs were reported in 17.5% of patients, most commonly endocrine disorders (thyroiditis, hypophysitis) and hepatic toxicities, which were generally manageable with corticosteroids [110]. In the CheckMate-040 trial, patients receiving the higher dose of ipilimumab showed increased toxicity, with grade ≥ 3 adverse events reported in 53% of cases, predominantly elevated liver enzymes and gastrointestinal complications [105].

Taken together, the combination of PD-1/PD-L1 and CTLA-4 inhibitors represents a powerful therapeutic strategy for advanced HCC, offering durable responses and prolonged survival. Ongoing clinical trials are focused on optimizing dosing regimens and refining patient selection to maximize clinical benefit while minimizing toxicity.

chemotherapy+ICI_s

An additional promising avenue for combination therapy is the use of ICIs alongside locoregional chemotherapy, including transarterial chemoembolization (TACE) or hepatic arterial infusion with the FOLFOX regimen (HAIC-FOLFOX). These localized treatments not only deliver direct cytotoxicity but also stimulate antitumor immunity by releasing tumor antigens and provoking local inflammation, which supports T-cell activation and infiltration [111].

In the Double-IA-001 trial (phase II, single-arm), patients with advanced HCC (BCLC stage C) received HAIC-FOLFOX combined with camrelizumab and sorafenib. The ORR was 44.0%, but the primary endpoint was not achieved, and the study did not progress to phase III, despite an acceptable safety profile [112].

In another single-arm phase II trial in China, 35 HBV-related HCC patients were treated with HAIC-FOLFOX plus camrelizumab and apatinib. Disease control was achieved in 97.1% of patients, with manageable grade ≥ 3 adverse events. Notably, 17% of patients achieved tumor downstaging sufficient for potentially curative resection. This regimen showed higher ORR and PFS compared with IMbrave150 and CARES-310, though limitations included a small sample size, lack of a control group, and restriction to HBV-related HCC [113].

A retrospective analysis of 51 unresectable HCC patients treated with HAIC-FOLFOX combined with ICIs (camrelizumab, pembrolizumab, or tislelizumab) plus tyrosine kinase or anti-VEGF agents reported a high conversion-to-surgery rate. Grade 3–4 adverse events occurred in 23.5% but were manageable, with no treatment-related deaths, supporting both efficacy and tolerability [114].

The LEAP-012 trial (phase III, multicenter, double-blind) evaluated TACE combined with lenvatinib and pembrolizumab versus TACE plus placebo in 480 patients. The experimental arm showed significantly improved PFS compared with TACE alone [115]. Similarly, a phase II study of TACE plus sintilimab demonstrated high ORR and DCR, with some patients eligible for conversion surgery. Adverse events were manageable, and OS follow-up is ongoing [116].

Finally, the EMERALD-1 trial (phase III, randomized, placebo-controlled) investigated TACE plus durvalumab with or without bevacizumab. The combination of TACE + durvalumab + bevacizumab significantly improved PFS compared with TACE alone, marking the first ICI-based global phase III trial to demonstrate clinically meaningful benefit in this setting [117].

ICI_s+radiotherapy

The integration of ICIs with radiotherapy (RT) represents a promising strategy to enhance therapeutic efficacy in HCC. Preclinical and translational studies have demonstrated that RT can convert the TME from an immunologically “cold” to a “hot” state by inducing the release of proinflammatory cytokines such as IFN-γ and upregulating immune costimulatory molecules, thereby potentiating ICI activity [118].

In a multicenter phase II trial, Koh et al. (2023) evaluated the combination of external beam radiotherapy (EBRT) with nivolumab in HCC patients with macrovascular invasion. Among 50 treated patients, the regimen achieved an ORR of 36%, a DCR of 74%, a median PFS of 5.6 months, and a median OS of 15.2 months, with grade ≥ 3 adverse events observed in only 12%, confirming an acceptable safety profile [119]. Similarly, a phase I pooled trial in 2023 randomized 13 advanced HCC patients after stereotactic body radiotherapy (SBRT, 40 Gy in 5 fractions) to nivolumab alone or nivolumab plus ipilimumab. The combination arm demonstrated superior ORR, PFS, and OS with manageable toxicity, underscoring the potential synergism of SBRT and dual checkpoint blockade [120].

The NASIR-HCC phase II study further explored selective internal radioembolization with yttrium-90 (^90Y SIRT) followed by nivolumab in 42 patients with unresectable, liver-confined HCC. After a median follow-up of 22.2 months, the combination showed clinically meaningful tumor shrinkage, prolonged OS, and improved time to progression, with grade 3–4 adverse events occurring in < 20%. Notably, some patients achieved downstaging sufficient to allow surgical intervention [121].

Retrospective analyses indicate that combining SBRT with PD-1 blockade may help overcome resistance to TACE. In this setting, patients receiving the combination achieved a median progression-free survival of 19.6 months and an objective response rate of 71%, compared with 10.1 months and 15.6% in the control arm [122]. These results underscore the potential of radiotherapy not only for local tumor suppression but also for triggering systemic antitumor effects through the abscopal phenomenon.

A recent systematic review and meta-analysis including 16 studies and 633 patients confirmed that RT plus ICIs is associated with higher ORR, median PFS, and OS compared to ICI monotherapy. Subgroup analyses showed improved outcomes with hypofractionated regimens (> 5 Gy per fraction), suggesting that higher RT doses may promote immunogenic cell death and enhance tumor antigen presentation. Furthermore, sequencing strategies appear critical: initiating RT before ICI administration yielded more favorable responses than the reverse order, likely due to RT-mediated priming of the tumor microenvironment. Importantly, patients with portal vein tumor thrombus (PVTT) also demonstrated improved survival with this combination approach [123].

Collectively, current evidence indicates that RT combined with ICIs achieves superior response and disease control compared to ICIs alone in advanced HCC. While larger randomized controlled trials are warranted to validate its survival benefit, the available data strongly support this combination as an effective and well-tolerated therapeutic strategy in selected patient populations.

Antitumor vaccines + ICIs

The integration of ICIs with antitumor vaccines or oncolytic viruses has recently emerged as a promising strategy to overcome therapeutic resistance in HCC [124]. Antitumor vaccines stimulate the immune system by presenting tumor-associated antigens, thereby enhancing the activation and expansion of tumor-specific T lymphocytes [125]. Oncolytic viruses selectively target and lyse cancer cells, leading not only to direct tumor elimination but also to immune activation through the release of tumor antigens and immunogenic cues [126]. Through these mechanisms, both approaches amplify antitumor T-cell activity and strengthen intratumoral immune responses, potentially leading to durable disease control [127].

The ongoing multicenter phase II TERTIO trial is evaluating the addition of the anti-telomerase vaccine UCPVax to atezolizumab plus bevacizumab in treatment-naïve patients with advanced HCC. By inducing CD4⁺ Th1 responses against telomerase, UCPVax aims to enhance tumor-specific immunity, potentially establishing a rationale for integrating antigen-specific vaccines with ICIs [128].

Similarly, a phase I/II trial investigated a personalized DNA plasmid vaccine (GNOS-PV02) encoding patient-specific neoantigens, co-administered with an IL-12 plasmid and pembrolizumab in patients with advanced HCC. The regimen was well tolerated and elicited robust neoantigen-specific T-cell responses, supporting the potential of personalized vaccines to enhance PD-1 blockade [129].

Oncolytic virotherapy has also been explored in combination with ICIs. In a pilot study, the oncolytic adenovirus H101 combined with nivolumab demonstrated early antitumor activity and favorable safety, highlighting a synergistic mechanism for augmenting PD-1–mediated immunity [130].

Overall, therapeutic cancer vaccines and oncolytic viruses represent innovative strategies to enhance T-cell priming, stimulate intratumoral immune activation, and broaden the therapeutic efficacy of ICIs in HCC. While current evidence is primarily derived from early-phase (I/II) clinical studies [131], several vaccine- and virotherapy-based regimens have demonstrated encouraging ORRs ranging from 30% to 90%, which substantially exceed the 15–25% typically observed with ICI monotherapy [132, 133]. Nonetheless, large-scale randomized trials remain essential to establish optimal sequencing, dosing strategies, and combination protocols. Furthermore, the identification of robust predictive biomarkers, such as tumor mutational burden and baseline immune cell infiltration, will be crucial for patient stratification and the optimization of clinical outcomes [134]. The synergistic interactions between immune checkpoint inhibitors and adjunctive therapies such as VEGF blockade, radiotherapy, and therapeutic vaccination are illustrated in Fig. 1. Selected ICI-based combination trials are summarized in Table 2.

Fig. 1.

Key Immune Pathways Targeted by Checkpoint Inhibitors in HCC. Overview of the major molecular pathways involved in ICI therapy for HCC, including PD-1/PD-L1–mediated suppression of T-cell effector function and CTLA-4 competition with CD28 for B7 ligands, reducing T-cell activation. The figure also summarizes mechanisms that enhance ICI response, such as VEGF/VEGFR-2–driven angiogenesis normalization, increasing immune infiltration, dual checkpoint blockade, chemotherapy-induced antigen release, radiotherapy-mediated immunogenic cell death, and vaccine or oncolytic virus–supported T-cell priming. These pathways illustrate the biological rationale for multimodal strategies to re-establish antitumor immunity in advanced HCC

Table 2.

Selected trials of immune-checkpoint–based combination therapy for hepatocellular carcinoma (HCC)

NCT	Phase/Design	Setting/Line	Regimen (Arms)	Primary endpoint(s)	Key results (primary endpoints)	Notable AEs (≥ G3)/Safety
NCT03764293 (CARES-310)	Phase III, RCT	Unresectable HCC, 1 L	Camrelizumab + rivoceranib vs. sorafenib	OS, PFS	OS 22.1 mo; PFS 5.6 mo; ORR 26.8% (combo superior)	Hypertension; ↑AST/ALT
NCT03794440	Phase II/III, RCT	Unresectable HCC (HBV+), 1 L	Sintilimab + bevacizumab biosimilar vs. sorafenib	OS (primary), PFS	PFS 4.6 vs. 2.8 mo; OS NR vs. 10.4 mo (favor combo)	Manageable; VEGF-class
NCT03713593 (LEAP-002)	Phase III, RCT	Unresectable HCC, 1 L	Lenvatinib + pembrolizumab vs. lenvatinib + placebo	OS, PFS (co-primary)	OS 21.2 vs. 19.0 mo; PFS 8.2 vs. 8.0 mo (NS)	Class-consistent; no new signals
NCT03937219 (COSMIC-312)	Phase III, RCT	Unresectable HCC, 1 L	Cabozantinib + atezolizumab vs. sorafenib	PFS (primary); OS (secondary)	PFS improved (HR 0.63); OS not statistically significant	TKI/VEGF-class AEs
NCT03298451 (HIMALAYA)	Phase III, RCT	Unresectable HCC, 1 L	STRIDE: tremelimumab (300 mg ×1) + durvalumab q4w vs. sorafenib	OS	5-yr OS 19.6% vs. 9.4%; ORR 20.1% vs. 5.1%	Grade ≥ 3 irAEs ~ 17.5%; manageable
NCT01658878 (CheckMate-040, combo cohorts)	Ph 1/2, multi-arm	Advanced HCC, post-sorafenib	Nivolumab + ipilimumab (various doses)	ORR, OS	ORR ~ 27%; OS 12.5 mo; 36-mo OS 26%	Grade ≥ 3 AEs up to ~ 53% in high-ipilimumab arm
NCT04039607 (CheckMate-9DW)	Phase III, RCT	Unresectable HCC, 1 L	Nivolumab + ipilimumab vs. lenvatinib or sorafenib	OS	OS 23.7 mo; ORR 36% vs. 13%; DOR 30.4 vs. 12.9 mo	Immune hepatitis (fatal cases reported in program); overall manageable
NCT03778957 (EMERALD-1)	Phase III, RCT	Intermediate HCC (BCLC B), TACE-eligible	TACE + durvalumab + bevacizumab vs. TACE + placebos (and TACE + durvalumab)	PFS	Median PFS 15.0 vs. 8.2 mo (combo vs. control); ORR 43.6% vs. 29.6%	VEGF-class; manageable
NCT04246177 (LEAP-012)	Phase III, RCT	Intermediate HCC, TACE-eligible	TACE + lenvatinib + pembrolizumab vs. TACE + placebos	OS, PFS	PFS 14.6 mo; ORR 46.8% (reported)	Class-consistent
NCT03006926	Phase 1b, single-arm	Unresectable HCC, 1 L	Lenvatinib + pembrolizumab	ORR, DOR (primary)	ORR 46%; DOR 8.6 mo; PFS 9.0 mo	No unexpected safety
NCT05185739	Phase II, randomized (neoadj ± adj)	Resectable HCC	Pembrolizumab or lenvatinib or both (peri-op)	Major pathologic response	No results reported	—
NCT04425226	Not App., prospective	Pre-transplant HCC (neoadjuvant)	Pembrolizumab + lenvatinib	Recurrence-free survival	12-mo RFS 87.5% vs. 37.5%	Transplant-specific safety monitored
NCT04988945	Phase II, single-arm	Unresectable HCC (downstaging)	TACE + SBRT → tremelimumab + anti-PD-L1	Efficacy; safety	Results pending	—
NCT04611165	Phase II, single-arm	Advanced HCC with macrovascular invasion	EBRT + nivolumab	PFS	PFS 5.6 mo; OS 15.2 mo; ORR 36%; DCR 74%	Grade ≥ 3 ~ 12%
NCT03380130 (NASIR-HCC)	Phase II, single-arm	Unresectable, liver-confined HCC	SIRT (Y-90) → nivolumab	Safety (primary), ORR/OS	ORR 40%; DCR 81%; OS 20.9 mo	SAEs 12%; discontinuation ~ 2.3%
NCT05528952 (TERTIO)	Phase II, RCT	Unresectable HCC, 1 L	Atezolizumab + bevacizumab ± UCPVax (anti-telomerase vaccine)	ORR	Ongoing; no results	—
NCT04251117	Phase 1/2, single-arm	Advanced HCC	Personalized DNA vaccine (GNOS-PV02) + IL-12 plasmid + pembrolizumab	Safety; immunogenicity	ORR 30.6%; median OS 19.9 mo; injection-site reactions 41.6%	Acceptable
Real-world (no NCT)	Retrospective cohort	BCLC B/C	TACE + PD(L)1 + TKI/anti-VEGF vs. TACE	PFS (primary)	PFS 9.5 vs. 8.0 mo; OS 19.2 vs. 15.7 mo; ORR 60.1% vs. 32.0%	Acceptable

Trials are organized by phase/design and clinical setting. For each study, the regimen, prespecified primary endpoint(s), and top-line results for primaries are shown; secondary outcomes are omitted unless explicitly highlighted in the manuscript text. Safety is summarized as grade ≥ 3 treatment-related adverse events. HCC, hepatocellular carcinoma; ICI, immune checkpoint inhibitor; PD-(L)1, programmed death-(ligand) 1; CTLA-4, cytotoxic T-lymphocyte–associated protein 4; TACE, transarterial chemoembolization; HAIC, hepatic arterial infusion chemotherapy; SBRT, stereotactic body radiotherapy; SIRT/TARE, yttrium-90 radioembolization; TKI, tyrosine-kinase inhibitor; ORR, objective response rate; DCR, disease control rate; PFS, progression-free survival; OS, overall survival; DOR, duration of response; HR, hazard ratio; mo, months; NR, not reported.

However, these ORR estimates largely derive from small, early-phase, often single-arm studies with heterogeneous eligibility criteria, response assessment methods, and follow-up duration; therefore, cross-trial comparisons to ICI monotherapy should be interpreted cautiously [135]. Moreover, feasibility and safety can be strongly influenced by underlying liver function, portal hypertension, and viral status [136]. To support real-world translation, randomized trials must demonstrate reproducible OS benefit, define the most effective sequencing with established SOC regimens, and incorporate robust immune correlatives to identify which patients truly gain incremental benefit [137].

ICI therapy resistance in HCC and strategies to overcome it

While some patients with HCC respond favorably to immune checkpoint inhibitors, resistance to these therapies continues to pose a significant clinical challenge. Both primary resistances, defined as the absence of initial response, and acquired resistance, disease progression after an initial response, limit the long-term efficacy of ICIs [138]. These forms of resistance often share overlapping mechanisms that arise from both intrinsic tumor cell factors and alterations within the immunosuppressive TME. The principal tumor-intrinsic and microenvironmental mechanisms contributing to ICI resistance in HCC are summarized in Fig. 2.

Fig. 2.

Mechanisms of Primary and Acquired ICI Resistance in HCC. This figure depicts intrinsic tumor factors, including Wnt/β-catenin activation, MAPK/ERK and PI3K/AKT/mTOR pathway signaling, STAT3-driven cytokine expression, JAK/IFN-γ defects, TP53 mutations, GPC3-mediated macrophage recruitment, and epigenetic repression reducing tumor immunogenicity. Extrinsic contributors include IL-8/CXCR2–mediated MDSC recruitment, T-cell exhaustion through LAG-3 and TIGIT pathways, and immunosuppressive activity from Tregs, CAFs, HSCs, and the gut microbiome. Potential solutions, such as next-generation checkpoint targets and pathway or epigenetic modulation, are highlighted as strategies to improve ICI responsiveness

Intrinsic factors

Intrinsic tumor mechanisms of resistance include the loss of tumor neoantigens or deficiencies in antigen presentation machinery, which impair T-cell recognition. In approximately 17% of HCC cases, the loss of HLA alleles disrupts MHC-mediated neoantigen presentation, directly compromising ICI efficacy [139].

The Wnt/β-catenin pathway plays a central role in driving immune escape and therapeutic resistance. Mutations affecting Wnt/β-catenin signaling (e.g., CTNNB1, AXIN1) occur in a substantial fraction of HCCs and result in pathway activation [140]. Clinical evidence indicates that HCC patients with such mutations fail to respond to programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) therapy, in contrast, nearly half of those without Wnt pathway alterations achieve durable disease control [141]. These clinical observations highlight aberrant Wnt/β-catenin signaling as a key driver of primary resistance [138].

Other oncogenic pathways, such as the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mechanistic target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), and signal transducer and activator of transcription 3 (STAT3) pathways, also contribute to immune escape. For instance, loss-of-function mutations in Janus kinase 1/2 (JAK1/2) impair interferon-gamma (IFN-γ) signaling, thereby reducing tumor antigen presentation and enabling adaptive resistance [142].

Glypican-3 (GPC3), expressed in ~ 70% of HCCs, facilitates tumorigenesis through TAM recruitment and apoptosis resistance. Retrospective biomarker analyses of clinical trials have linked elevated GPC3, AFP, and activated β-catenin expression with reduced response to PD-1 blockade [124, 143]. Similarly, Tumor Protein p53 (TP53) mutations, frequently detected in HCC, are associated with reduced immune infiltration and an immunosuppressive TME. In particular, TP53-mutated “intermediate-class” tumors display immune exclusion phenotypes, underscoring TP53’s role in mediating immune evasion [144]. Persistent activation of STAT3 signaling enhances immunosuppression by driving cytokines such as TGF-β, Interleukin-17 (IL-17), and VEGF, while suppressing type I interferon responses and NK cell activity [124].

Finally, epigenetic modifications, such as DNA hypermethylation, reduce tumor immunogenicity by limiting antigen presentation. Preclinical studies in HCC mouse models have shown that combining histone deacetylase inhibitors (e.g., belinostat) with ICIs can restore antigen presentation and augment antitumor effects, suggesting a potential therapeutic avenue to overcome epigenetic-driven resistance [145].

Extrinsic factors

As detailed in Sect. 2, immunosuppressive cellular programs in the HCC TME (e.g., Tregs and myeloid-lineage populations) shape antitumor immunity; here we focus on extrinsic mechanisms specifically linked to primary and acquired resistance to ICIs. The host’s immune homeostasis strongly influences these factors. In HCC, higher infiltration of Tregs has been correlated with reduced OS and disease-free survival (DFS) [146].

In chronic hepatitis, MDSCs play a key role in limiting the efficacy of ICIs by dampening antitumor immune activity through multiple mechanisms [147]. Among inflammatory cytokines, interleukin-8 (IL-8) plays a pivotal role in HCC progression, in part by recruiting immunosuppressive myeloid cells [148]. A single-cell RNA sequencing (scRNA-seq) study in advanced HCC demonstrated that IL-8 and its receptor C-X-C motif chemokine receptor 2 (CXCR2) are predominantly derived from MDSCs. Elevated circulating IL-8 levels are associated with poor responses to ICI therapy. Moreover, preclinical models have shown that activation of the IL-8/CXCR2 axis induces resistance to PD-L1 blockade. The selective CXCR2 inhibitor AZD5069 has demonstrated efficacy in mouse models, where its combination with anti–PD-L1 therapy resulted in tumor regression, prolonged survival, and increased intratumoral CD8⁺ T-cell infiltration. These findings suggest that CXCR2 inhibition may represent a promising strategy to overcome ICI resistance [149].

Other inhibitory immune checkpoint molecules also contribute to immune evasion.

Lymphocyte activation gene-3 (LAG-3) is frequently overexpressed in HCC, leading to T-cell exhaustion [150]. Exhausted CD4⁺ and CD8⁺ tumor-infiltrating lymphocytes then display impaired cytokine production [151].

Similarly, T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is expressed on NK cells, natural killer T (NKT) cells, CD8⁺ T cells, regulatory T cells (Tregs), and memory CD4⁺ T cells [152]. Its upregulation, often driven by CD155 overexpression in HCC, creates a metabolic barrier that suppresses T-cell function [153]. Preclinical studies suggest that combined blockade of TIGIT and LAG-3 can restore T-cell activity and improve antitumor immunity [152].

Additional extrinsic factors include HSCs and CAFs, both of which contribute to immune suppression and therapeutic resistance. The gut microbiome is another crucial determinant of immunotherapy response, as it influences systemic immune activity and T-cell infiltration into tumors [154]. Notably, the administration of antibiotics, proton pump inhibitors, or corticosteroids prior to or concomitant with ICI treatment has been associated with diminished therapeutic efficacy [155, 156].

Integrated molecular analyses of tumor biopsies from 358 patients enrolled in the GO30140 phase Ib and IMbrave150 phase III trials, who received atezolizumab plus bevacizumab, atezolizumab monotherapy, or sorafenib, revealed that higher expression of PD-L1, T-effector gene signatures, and increased intratumoral CD8⁺ T-cell density correlated with improved clinical outcomes. Conversely, a high regulatory-to-effector T-cell ratio and the expression of oncofetal genes such as glypican-3 (GPC3) and alpha-fetoprotein (AFP) were associated with reduced therapeutic benefit. Importantly, enhanced efficacy of atezolizumab plus bevacizumab over atezolizumab monotherapy was linked to higher expression of vascular endothelial growth factor receptor 2 (VEGFR2, also known as KDR), elevated Treg levels, and enriched myeloid inflammatory signatures [143].

Collectively, numerous extrinsic mechanisms of immunotherapeutic resistance have been identified, with new pathways continuing to emerge. A deeper understanding of these resistance mechanisms is critical to refine therapeutic strategies and optimize patient outcomes [138].

Strategies to overcome ICI resistance

Several therapeutic approaches have been explored to overcome ICI resistance in HCC, including combination therapies, novel immune checkpoint targets, innovative immunotherapies, and biomarker-driven strategies [96, 157, 158]. Targeting novel immune checkpoints represents one promising approach. In a single-arm phase II trial, anti-PD-1 therapy was combined with Bavituximab, an antibody against phosphatidylserine, a molecule with immunosuppressive and anti-inflammatory properties. Targeting membranous phosphatidylserine can induce proinflammatory and immune-stimulating responses, enhancing ICI efficacy. The combination demonstrated synergistic effects with pembrolizumab, although further validation is needed. Baseline tumor analyses revealed reduced B cells, fibrotic stroma, and immunosuppressive molecules, correlating with favorable responses [159].

Preclinical studies using mouse models of HCC with Transformation-related protein 53 (Trp53) deletion and elevated Cellular Myelocytomatosis oncogene (C-Myc) expression demonstrated that silencing Poliovirus Receptor-Related 1 (Pvrl1) and Poliovirus Receptor-Related 3 (Pvrl3) genes, combined with anti-PD-1 and anti-TIGIT therapy, significantly inhibited tumor growth. Anti-PD-1 monotherapy was insufficient, and CD8⁺ memory T cells within tumors expressed inhibitory receptors (PD-1, LAG-3, TIGIT), indicative of exhaustion. Dual blockade of PD-1 and TIGIT enhanced cytotoxic T-cell infiltration, improved the cytotoxic-to-Treg ratio, and prolonged survival [153].

Similarly, the combination of anti-PD-1 with Pegylated interferon-alpha (Peg-IFNα) improved T-cell infiltration and extended survival in both subcutaneous and orthotopic HCC mouse models compared to PD-1 monotherapy [160]. Targeting tumor-associated pathways can also restore ICI responsiveness. The cholecystokinin-B receptor (CCK-BR) is overexpressed in HCC. In mouse models, the CCK-BR antagonist proglumide, alone or with anti-PD-1, reduced peritumoral fibrosis, increased intratumoral CD8⁺ T-cell infiltration, improved survival, and modulated genes related to fibrosis and epithelial-to-mesenchymal transition [161].

Immune checkpoint co-targeting strategies include LAG-3 and TIGIT inhibition. Relatlimab, an LAG-3 inhibitor, rejuvenates exhausted T cells and enhances antitumor immunity [162]. TIGIT, interacting with CD155 on antigen-presenting cells, suppresses T- and NK-cell activity [163]. TIGIT inhibitors such as ociperlimab and tiragolumab show potential alone or combined with PD-(L)1 blockade [164].

Other emerging strategies involve oncolytic viruses, vaccines, and cell therapies, which can convert non-inflammatory tumor microenvironments into immunologically “hot” ones [165]. Inhibition of TGF-β signaling with agents such as Galunisertib enhances sensitivity to anti-PD-L1 therapy [166]. Epigenetic modulation also contributes to overcoming resistance. DNA methyltransferase inhibitors (e.g., azacitidine, decitabine) restore major histocompatibility complex (MHC) class I expression, enhance antigen presentation, and promote antitumor immunity [167]. Histone deacetylase inhibitors (e.g., vorinostat, panobinostat) can reverse immune escape mechanisms [168].

Finally, HCC associated with non-alcoholic steatohepatitis (NASH) is less sensitive to ICIs. Neutrophils expressing CXCR2 are enriched in NASH-HCC; CXCR2 antagonists combined with anti-PD-1 therapy reduce tumor burden and improve survival [169]. Overall, durable benefit from ICIs in HCC is limited by heterogeneous resistance mechanisms, underscoring the need for combination therapies, pathway-targeted interventions, and immunomodulatory strategies.

Predictive biomarkers and patient selection for ICI-based therapy in HCC

Exploratory biomarker work from the atezolizumab-based development program in HCC, spanning GO30140 and the registrational IMbrave150 dataset, has provided a practical starting point for biomarker hypotheses. Across these analyses, response and longer survival were generally enriched in tumors with an “inflamed” immune contexture, including higher T-effector–related transcriptional programs and greater intratumoral CD8⁺ T-cell infiltration, whereas reduced benefit was associated with immune-suppressive features (e.g., higher Treg/effector imbalance and myeloid inflammation) and oncofetal gene programs such as AFP/GPC3-high states. Importantly, signals suggesting a distinct contribution of VEGF blockade have been reported: improved outcomes with the addition of bevacizumab appeared to track with angiogenesis/myeloid/Treg-linked features (e.g., higher VEGFR2/KDR expression and myeloid inflammation signatures), consistent with anti-VEGF–mediated vascular/immune reprogramming [143, 170].

More recent translational studies further support that specific immune-cell states and chemokine programs (e.g., CXCL10-associated macrophage states and effector-memory CD8⁺ subsets) can correlate with clinical benefit on atezolizumab–bevacizumab [171, 172]. Despite being biologically compelling, these candidates are not yet clinical-grade: tissue availability is limited in cirrhotic patients, spatial heterogeneity and sampling site strongly influence readouts, immune states evolve dynamically on therapy, and assay/platform differences complicate reproducible cutoffs. Most critically, prospective validation demonstrating that a given biomarker reliably selects one ICI-based regimen over another (rather than reflecting general prognosis) remains incomplete [173].

Tumor-intrinsic alterations can shape immune visibility and exclusion phenotypes, influencing ICI responsiveness even when therapies target the TME. Wnt/β-catenin pathway activation (often via CTNNB1-class tumors) has been repeatedly linked to immune exclusion (“cold” tumors) and primary resistance patterns in HCC, providing a mechanistic rationale for inferior ICI activity in this molecular class [174, 175]. In parallel, defects in antigen presentation, such as HLA class I loss of heterozygosity reported in a subset of multifocal HCC, may impair neoantigen presentation and facilitate immune escape, conceptually limiting the ceiling of ICI benefit [139, 176]. TP53-altered tumors have also been associated with immune signaling perturbations (including checkpoint pathway regulation) and may contribute to immune evasion phenotypes, although clinical-predictive use of TP53 status remains inconsistent and context-dependent [177]. Overall, these genomic factors are best viewed as resistance-enriching features and should be interpreted cautiously until prospectively linked to treatment selection and clinically actionable thresholds.

Blood-based markers are attractive because they are scalable, can be monitored longitudinally, and may capture systemic inflammation and myeloid-driven immunosuppression—two themes tightly linked to ICI resistance in HCC. Among circulating cytokines, IL-8 is notable: clinical data suggest that baseline levels and, importantly, early on-treatment increases in serum IL-8 (within the first weeks of ICI therapy) can correlate with inferior response and worse survival in unresectable HCC [148]. Mechanistically, IL-8–CXCR1/2 (particularly CXCR2) signaling can promote recruitment and activity of suppressive myeloid populations, and targeting this axis has shown the potential to sensitize anti-PD-(L)1 therapy in translational HCC models [149]. Nonetheless, circulating markers face major confounders in HCC (cirrhosis severity, infection/viral status, portal hypertension, and baseline systemic inflammation), and standardized timing, platforms, and cutoffs are still evolving—so these markers are not yet sufficient as stand-alone decision tools.

In routine practice, no single biomarker is definitively validated to select HCC patients for a specific ICI-based regimen. The most realistic near-term path is composite, regimen-relevant models that integrate (i) tumor immune contexture (T-effector/CD8⁺ features; suppressive myeloid/Treg signals), (ii) key resistance-enriching genomic states (e.g., Wnt/β-catenin activation; antigen-presentation defects), and (iii) dynamic blood markers of myeloid inflammation (e.g., IL-8 trajectories), alongside essential clinical constraints (liver function and bleeding risk). Validation will require prospective biomarker-integrated trials with pre-specified endpoints, harmonized assays, and reproducible thresholds that demonstrate true predictive utility (treatment interaction), not merely prognosis [173].

ICI therapy complications in HCC

ICIs have transformed cancer therapy, but their use in HCC is associated with notable complications that require careful management. Immune-related adverse events (irAEs) are common and range from mild symptoms (fatigue, rash, diarrhea) to organ-specific toxicities such as hepatitis and hypothyroidism. Severe but rare events such as myocarditis, pneumonitis, encephalitis, myositis, myelitis, and hypersensitivity reactions have also been reported [178]. In a meta-analysis of 6,472 patients from 47 studies, 83.4% experienced treatment-related adverse events (trAEs) of any grade, with 33% being grade ≥ 3. The incidence of irAEs was 34% for any grade and 9% for grade ≥ 3. Elevated aspartate aminotransferase (AST) was the most frequent treatment-related adverse event (38%), whereas fatigue was the most common irAE (14%) [179].

In the IMbrave150 trial, hypertension, elevated AST, fatigue, and proteinuria were among the most common complications. Serious adverse events included gastrointestinal bleeding, infections, and fever. Bevacizumab-related VEGF inhibition may increase bleeding risk, especially in portal varices, highlighting the importance of screening and treatment before initiating Atezolizumab plus Bevacizumab [180]. In the CheckMate040 trial with Nivolumab and Ipilimumab, trAEs included rash, diarrhea, fatigue, hypothyroidism, adrenal insufficiency, and reduced appetite, with one fatal case of grade 5 pneumonitis. Other fatal events have been documented, including gastric ulcer perforation, sepsis, myocarditis, respiratory distress, nervous system disorders, myasthenia gravis, and esophageal variceal hemorrhage [105].

Notably, patients who developed irAEs frequently demonstrated longer progression-free survival, though overall survival outcomes were less consistent. Thyroid complications such as thyroiditis were associated with improved OS, PFS, and ORR, suggesting stronger antitumor immune activation. Significantly, steroid treatment for irAEs did not reduce therapeutic efficacy [178].

Immune-mediated liver injury (ILICI) is another significant complication, typically occurring 4–12 weeks after ICI initiation in a study of 207 HCC patients, liver injury manifested as cholestatic (65.4%), hepatocellular (11.5%), or mixed (23.1%) patterns. Risk factors included diabetes, cirrhosis, and multifocal tumors [181]. In the CheckMate-9DW trial, four patients died of immune-mediated hepatitis [108]. Autoimmune hepatitis (AIH) may also arise under ICI therapy. While rare, it can mimic ICI-induced hepatotoxicity. Distinguishing features include autoantibodies, histology, treatment response, and the presence of other irAEs [182]. Symptoms are often nonspecific, such as fatigue, malaise, abdominal pain, or jaundice.

Additional autoimmune manifestations include new-onset autoimmune thyroiditis (e.g., Graves’ disease) and rare hematologic disorders such as immune thrombocytopenia and Evans syndrome [178]. Another important complication is viral reactivation. A meta-analysis of 34 studies with 7,126 patients reported a 1.3% rate of HBV reactivation, with higher risk in HCC patients, HBV carriers, and those from Asia or developing regions [183]. In the CheckMate-040 study, no HBV reactivation was observed in patients receiving antiviral prophylaxis [182]. Thus, HBV and HCV screening is recommended before ICI initiation, and nucleoside analog prophylaxis should be started in HBsAg-positive patients [182], [183].

Overall, ICIs can induce toxicities in multiple organs. While most events are low-grade, about one-third of patients experience serious complications such as esophageal varices, severe colitis, pneumonia, and myocarditis. Careful monitoring of liver function and patient symptoms is therefore essential [179].

Conclusion

Immunotherapy has rapidly evolved from an experimental concept to a cornerstone of systemic therapy in HCC. Clinical evidence demonstrates that ICIs, particularly those targeting PD-1/PD-L1 and CTLA-4, can induce durable and clinically meaningful responses in a subset of patients, though the overall benefit of monotherapy remains limited. Combination strategies, most notably atezolizumab plus bevacizumab (IMbrave150), tremelimumab–durvalumab (STRIDE), and nivolumab plus ipilimumab (CheckMate-9DW), have established new standards of care, significantly improving overall survival with manageable toxicity. Additional approaches, including pairing ICIs with TKIs, anti-VEGF agents, radiotherapy, or locoregional therapies such as TACE and HAIC, further expand treatment options and enhance immune activity. Emerging modalities such as therapeutic vaccines, oncolytic viruses, bispecific antibodies, and adoptive cell therapies (e.g., CAR-T cells) highlight the potential to overcome resistance and reshape the immunosuppressive tumor microenvironment. Nonetheless, resistance remains a significant challenge, driven by tumor-intrinsic mechanisms (such as β-catenin signaling and impaired antigen presentation) and microenvironmental factors (including Tregs, MDSCs, CAFs, and cytokine networks).

Effective management of immune-related adverse events, particularly hepatic toxicities and bleeding risks associated with anti-VEGF combinations, is essential for safe clinical application. Looking ahead, research priorities include the validation of predictive biomarkers, optimization of treatment sequencing across liver-function strata, and randomized trials of multimodal regimens that align mechanistic insights with patient biology.

Overall, immunotherapy has transformed the therapeutic landscape of HCC, paving the way toward personalized, durable, and multimodal treatment strategies. Integrating mechanistic understanding with clinical advances will be key to extending long-term survival benefits to a broader patient population.

Author contributions

Saeed Khavari Khorasani and Siavash Boroumandi contributed equally to the conception, literature review, data collection, and drafting of the manuscript. Ali Darzi and Mahla Shokouhfar participated in writing, editing, and organizing references. Pedram Abdali contributed to writing, scientific review, and final proofreading. Pooya Eini designed the figures and assisted with visual editing. Ahmad Ghorbani Vanan and Nastaran Bahrami conceived the main idea, supervised the project, critically revised the manuscript, and finalized it for submission. All authors contributed to the writing of the manuscript and approved the final version.

Funding

This research received no grant from any funding agency, commercial or not-for-profit sectors.

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The authors declare no competing interests.

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