Low-intensity pulsed ultrasound activated the anti-tumor immunity by irradiating the spleen of mice in 4 T-1 breast cancer.

Tumor immunotherapy is booming around the world. However, strategies to activate the immune system and alleviate the immunosuppression still need to be refined. Here, we demonstrate for the first time that low-intensity pulsed ultrasound (LIPUS, spatial average time average intensity (Isata) is 200 mW/cm2, frequency is 0.3 MHz, repetition frequency is 1 kHz, and duty cycle is 20%) triggers the immune system and further reverses the immunosuppressive state in the mouse models of breast cancer by irradiating the spleen of mice. LIPUS inhibited tumor growth and extended survival in mice with 4 T-1 tumors. Further studies had previously shown that LIPUS enhanced the activation of CD4+ and CD8+ T cells in the spleen and led to significant changes in cytokines, as well as induced upregulation of mRNA levels involved in multiple immune regulatory pathways in the spleen. In addition, LIPUS promoted tumor-infiltrating lymphocyte accumulation and CD8+ T cell activation and improved the dynamics of cytokines/chemokines in the tumor microenvironment, resulting in a reversal of the immunosuppressive state of the tumor microenvironment. These results suggest a novel approach to activate the immune response by irradiating the spleen with LIPUS.