Microwave ablation (MWA) is an effective treatment for liver cancer (LC), but its impact on distant tumors remains to be fully elucidated. This study investigated the abscopal effects triggered by MWA treatment of LC, at different power levels and with or without combined immune checkpoint inhibition (ICI). We established a mouse model with bilateral subcutaneous LC and applied MWA of varied power levels to ablate the right-sided tumor, with or without immunotherapy. Left-sided tumor growth was monitored to assess the abscopal effect. Immune cell infiltration and distant tumor neovascularization were quantified via immunohistochemistry, revealing insights into the tumor microenvironment and neovascularization status. Th1- and Th2-type cytokine concentrations in peripheral blood were measured using ELISA to evaluate systemic immunological changes. It was found that MWA alone, especially at lower power, promoted distant tumor growth. On the contrary, combining high-power MWA with anti-programmed death (PD)-1 therapy promoted CD8+ T-cell infiltration, reduced regulatory T-cell infiltration, upregulated a Th1-type cytokine (TNF-α) in peripheral blood, and inhibited distant tumor growth. In summary, combining high-power MWA with ICI significantly enhances systemic antitumor immune responses and activates the abscopal effect, offering a facile and robust strategy for improving treatment outcomes.
Keywords: PD-1; abscopal effect; immunotherapy; liver cancer; microwave ablation.