Interleukin-33 alleviates the immunosuppressive tumor microenvironment and enhances anti-programmed death ligand-1 immunotherapy efficacy in hepatocellular carcinoma.

Background

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies worldwide. The immunosuppressive tumor microenvironment (TME) and limited response to immune checkpoint blockade (ICB) therapy remain major obstacles to improving HCC prognosis. Interleukin-33 (IL33) is a multifunctional cytokine that plays critical roles in cancer development; however, its function in HCC remains unclear.

Methods

Cell proliferation was evaluated using colony formation and 5-ethynyl-2'-deoxyuridine (EdU) staining assays. Tumor-bearing models were established in both immunocompetent and immunodeficient mice. Multiplex immunofluorescence and flow cytometry were performed to assess TME characteristics. RNA sequencing and Western blot analyses were conducted to investigate the underlying mechanisms.

Results

We found that IL33 downregulation was significantly associated with shorter survival in patients with HCC. IL-33 treatment markedly inhibited tumor progression, whereas endogenous IL-33 blockade accelerated tumor growth in immunocompetent mice. However, IL-33 showed no significant effect on cell proliferation in vitro and failed to suppress tumor growth in immunodeficient mice lacking T cells. IL-33 administration notably reduced immunosuppressive tumor-associated macrophages and myeloid-derived suppressor cells, while substantially increasing CD8+ T cells, particularly functional interferon (IFN)-γ+CD8+ T cells, within the TME. Mechanistically, IL-33 activated the stimulator of interferon genes/interferon regulatory factor signaling axis, enhanced IFN-γ secretion, and inhibited RICTOR and programmed death 1 expression in mouse tumors. Furthermore, HCC specimens with high IL-33 expression exhibited more tertiary lymphoid structures. In addition, combined IL-33 and anti-programmed death ligand-1 therapy synergistically reduced tumor burden and further enhanced antitumor immunity in vivo.

Conclusion

These findings indicate that IL-33 alleviates immunosuppression and enhances ICB efficacy, providing novel insights into its role in HCC immunotherapy.