Volumetric Nanodroplet‐Enhanced Ultrasound Surgery Combined with Immune Checkpoint Inhibition as a Cancer Therapy Platform

Abstract Immune checkpoint inhibitors hold promise, yet their efficacy in solid tumors is limited by the complex tumor microenvironment and the lack of immune cell infiltration. This study aims to enhance immunotherapy by combining anti PD‐1 checkpoint inhibition therapy with nanodroplet‐mediated histotripsy. The proposed method involves systemic injection of nanodroplets, which accumulate within tumors. These nanodroplets are then activated into cavitating gas bubbles using a rotating imaging probe, followed by low‐frequency ultrasound application. This process induces tumor fractionation, facilitating the shift of the tumor microenvironment from cold to hot. Tumor ablation results show extensive lesions within the cancerous tissues, demonstrating the effectiveness of the ablation treatment. The combined approach of nanodroplets, ultrasound and anti PD‐1 yielded a significant reduction in tumor growth compared to control groups. Immunohistochemistry analysis reveals an increase in F4/80+ macrophages and CD8+ T cells in the treated tumor group, indicating an enhanced immune response. F4/80+ macrophages reached 21.36% ± 3.4%, while CD8+ T‐cell recruitment achieved 6.76% ± 4.5%, representing a 6.8‐ and a 5.5‐fold increase compared to the control group, respectively. This approach demonstrates the potential to overcome key barriers in solid tumor treatment by combining precise mechanical disruption with systemic immune activation.