21169 Background: Previous results have shown that high intensity focused ultrasound (HIFU) ablation can potentially activate a host anti-tumor immunity. This study was to investigate whether acoustic cavitaion may enhance host immune responses after HIFU treatment for solid malignancy, and to explore the potential mechanisms regarding the enhanced anti-tumor immunity. Methods: (1) Tumor cell vaccine preparation: H22 cells were irradiated with HIFU (0.8MHz, 1050W/cm2, 90s); H22 cells were heated for one hour in 65°C water bath. (2) Animal study: 150 KM mice were randomly divided into three groups: control group, thermal group, and HIFU group. Each group had 50 mice for immune experiments. By using hypodermic injection, the mice in thermal group and HIFU group received either 0.2ml heat-treated H22 vaccine or 0.2ml HIFU-treated H22 vaccine in the left flank of each mouse. Those in control group received only injection with same amount of saline solution. The vaccination times were 4 sessions, once a week for 4 consecutive weeks. One week after last vaccination, each mouse was challenged with H22 tumor cells. All mice were followed up to observe the long-term survival in each group, and peripheral blood was collected to detect changes in T lymphocytes and their subsets by flow cytometry technique. Results: The tumor incidences and 6-week survival rates were observed 100% and 88% of mice in control group, 72.5% and 40% in thermal group, and 42.5% and 14% in HIFU group respectively. Compared to the values in either control group or thermal group, there was a significant decrease of tumor incidences and 6-week survival rates in HIFU group. The volume of tumor was obviously lower in HIFU group, and a significant difference was observed between HIFU group and thermal group or control group. Compared to the values in control group, there were a significant increase of CD4+ levels and CD4+/CD8+ ratio, and a significant decrease of CD8+ level in both HIFU group and thermal group. Conclusions: Antitumor immune response could be enhanced after HIFU ablation for H22 implanted tumor in mice, and acoustic cavitation could play an important role to stimulate host antitumor immune system. No significant financial relationships to disclose.
High-intensity focused ultrasound (HIFU) ablation by the frequency chirps: Enhanced thermal field and cavitation at the focus
