DDEL-10. MICROBUBBLE-ENHANCED FOCUSED ULTRASOUND REGULATES THE ENRICHMENT OF INFLAMMATORY PATHWAYS IN THE BLOOD-BRAIN BARRIER AND IMPROVES CAR T CELL ACCUMULATION IN GLIOMAS

Abstract A major challenge to brain cancer immunotherapy is posed by the rate-limiting obstacles to the systemic delivery of cytotoxic T cells, such as chimeric antigen receptor (CAR) T cells, in brain tumors posed by the blood brain barrier (BBB). Although the BBB can be bypassed by direct infusion of CAR-T cells in brain tumors, these approaches offer only short-term benefits, since they cannot affect distant tumor cell infiltrations, as evidenced by tumor relapse. Circulating microbubbles (MB) upon ultrasound (US) exposure (sonication) can exert mechanical stress in brain vessels to trigger a range of responses, including local increase in the BBB permeability and activation of inflammatory signaling and phenotypes. We hypothesize that ultrasound frequency tuned at MB resonance inside brain capillaries can transiently modulate the BBB signaling and function to improve CAR-T cell trafficking in glioma tumors. RNAseq and immunostaining of protein expression reveal that at frequencies just above microbubble resonance inside vessels (1.5MHz for 2µm MB), where maximum vessel wall shear stress is observed, there is a marked enrichment of inflammatory markers in the endothelial cells of brain vessels, including P-selectin and ICAM-1. Consistent with these findings, we observed that under high frequency excitation (1.5MHz), there is a 5-fold increase in the accumulation of EGFRvIII CAR-T cells in orthotopic EGFRvIII murine glioma tumors as compared not sonicated controls. We also found that over 85% of the tumor-infiltrating CAR-T cells express PSGL-1 and LFA-1 receptors, which interact with P-selectin and ICAM-1 to facilitate T cell extravasation. Together, these findings demonstrate that tuning the US frequency can improve CAR-T cell trafficking, potentially through upregulation of cell adhesion molecules in the glioma tumor microenvironment, and further support the functional relevance and potential clinical significance of the observed immuno-mechano-biological changes.