This study demonstrates that cytokine IL-33 alleviates the immunosuppressive tumor microenvironment in hepatocellular carcinoma, activates the STING/IRF axis, increases functional CD8+ T cells and TLSs, and synergizes with anti-PD-L1 to boost antitumor immunity, offering a promising strategy to enhance HCC immunotherapy.
Hepatocellular carcinoma (HCC) remains one of the deadliest malignancies worldwide, with limited treatment options and a poor prognosis. A major barrier to improving patient outcomes lies in the immunosuppressive tumor microenvironment (TME) of HCC, which impairs anti-tumor immunity and reduces the effectiveness of immune checkpoint blockade (ICB) therapies such as programmed death ligand-1 (anti-PD-L1). While the multifunctional cytokine IL-33 has been shown to play important roles in various cancer types, its specific function and underlying mechanism in HCC have long remained unclear—until now, according to a new study focusing on IL-33's role in reshaping TME and enhancing ICB efficacy.
To unravel IL-33's function in HCC, the research team conducted a series of comprehensive experiments combining in vitro and in vivo approaches. In vitro, cell proliferation was evaluated using colony formation and 5-ethynyl-2'-deoxyuridine staining. In vivo, tumor-bearing models were established in both immunocompetent and immunodeficient mice to assess IL-33's impact on tumor growth under different immune conditions. Additionally, multiple immunofluorescences and flow cytometry were used to analyze TME states, while RNA sequencing and Western blot helped uncover the molecular mechanisms underlying IL-33's effects.
The results yielded striking findings: IL-33 downregulation in patients with HCC was significantly associated with shorter survival times, indicating its potential as a prognostic marker. In immunocompetent mice, IL-33 treatment markedly slowed tumor progression, whereas blocking endogenous IL-33 accelerated tumor growth. Notably, IL-33 had no obvious effect on HCC cell proliferation in vitro and failed to inhibit tumor growth in immunodeficient mice lacking T cells, suggesting its anti-tumor effects depend on a functional immune system.
Further analysis of the TME revealed that IL-33 treatment significantly reduced the number of immunosuppressive cells—including tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs)—while dramatically increasing CD8+ T cells, particularly functional interferon (IFN)-γ+CD8+ T cells that play a key role in anti-tumor immunity. Mechanistically, the team found that IL-33 exerts its effects by activating the stimulator of interferon genes (STING)/interferon regulatory factor (IRF) axis, increasing IFN-γ secretion, and inhibiting Rictor and programmed death 1 (PD-1) expression in mouse tumors.
Another key discovery was that HCC specimens with high IL-33 levels contained more tertiary lymphoid structures (TLSs), which are closely linked to enhanced anti-tumor immunity and better treatment responses. Most importantly, combining IL-33 with anti-PD-L1 therapy synergistically reduced tumor burden and further boosted anti-tumor immunity in vivo, highlighting its potential to overcome ICB resistance in HCC.
The study's conclusions shed new light on IL-33's role in HCC, demonstrating that this cytokine can alleviate immunosuppression and enhance ICB response. These findings not only deepen our understanding of HCC's immunopathogenesis but also provide a promising new strategy for optimizing immunotherapy in patients with HCC, offering hope for improving the prognosis of this deadly disease.
