In vivo tracking of CAR-T cells in tumors via nanobubble-based contrastenhanced ultrasound

CAR-T cell therapy has led to remarkable advances in the outcomes of patients with acute lymphoblastic leukemia (ALL), B cell lymphomas, and multiple myeloma. Given these successes in hematologic malignancies, extensive efforts are now focused on developing CAR-T cell therapies for the treatment of solid tumors. The treatment of solid tumors poses significant hurdles with cell trafficking that is necessary to achieve efficacy and minimize off-tumor side effects. The development of simple, safe and inexpensive modalities to track CAR-T cell distribution in humans could provide critical insights to facilitate the development of improved CAR-T products for solid tumors. Here we demonstrate a strategy to monitor CAR-T cells in vivo using ultrasound imaging and nanobubble (NB) labeled cells. NBs are ultrasound contrast agents composed of a lipid shell and a C4F10 gas core that can be efficiently internalized into cells. This approach enables us to image the CAR-T cells using nonlinear contrast-enhanced ultrasound (CEUS). Utilizing this method, we found that CAR-T cells can be visualized after injection into both tumor bearing and non-tumor bearing mice. In summary, our ultrasound-based tracking approach can effectively monitor the trafficking of CAR-T cells in vivo, offering a valuable new strategy that can further enable the development of new CAR-T products and strategies to modulate cell trafficking.