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 to treat solid tumors. The treatment of solid tumors poses significant hurdles with cell trafficking necessary to achieve efficacy and minimize off-tumor side effects. The development of simple, safe and inexpensive modalities for tracking CAR-T cell distribution in clinical use in vivo 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 of 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.
