Leveraging Nanobubble-Mediated Ultrasound to Improve CAR-T Efficacy in Solid Tumor Treatment

Solid tumors remain difficult to treat due to their dense tissue and protective microenvironment, which limit therapeutic efficacy. While chimeric antigen receptor (CAR) T-cell immunotherapy has revolutionized blood cancer treatment, its success in solid tumors is hindered by poor T-cell infiltration. To address this, we propose synergistically combining CAR-T cells with nanobubble-mediated ultrasound mechanotherapy to enhance therapeutic outcomes. Nanobubbles, which accumulate in tumors after systemic injection, are activated by low-frequency ultrasound to induce tumor fractionation, facilitating CAR-T cell infiltration and improving efficacy against both the tumor and its microenvironment. In vitro experiments using breast cancer cells established the effectiveness of combining nanobubble-mediated low-energy ultrasound with CAR-T therapy. The combination treatment reduced cell viability to 2% and increased IFNγ secretion, indicative of enhanced immune activation. In vivo experiments where CAR-T cells were injected after ultrasound + nanobubbles treatment, showed a significant increase in tumor fractionation, and immune cell infiltration into the tumor microenvironment, with a twofold increase in the detection of CD45, CD4, and CD8 immune cells. Additionally, there was a significant increase in survival (p<0.0001). The surviving mice were rechallenged with tumor cells after 160 days of recovery and showed no signs of tumor development, indicating the establishment of long-lasting tumor-specific immunity. Overall, this integrated approach not only reduces tumor burden but also improves immune cell recruitment and facilitates CAR-T cell infiltration into the tumor core, significantly enhancing CAR-T cell cytotoxicity and immune memory against tumor cells. This method holds great promise for overcoming current barriers in solid tumor treatment.