Feasibility of using ultrasound with microbubbles to purify cell lines for immunotherapy application

Cell-based immunotherapies exploit cell surface antigens to identify and purify cell lines. Fluorescence-based sorters require large sample volumes and are too costly for small labs. Magnetic sorters require enzymatic digestion to remove magnetic particles. We propose to label cells with antibody-conjugated microbubbles (MBs) and selectively sort them using ultrasound. After sorting, the MBs can be removed by a small overpressure. TargeStar-SA microbubbles (MBs) were conjugated to leukemia cells expressing CD7 antigens. Conjugated cell suspensions were placed in a flow with erythrocytes (which lack CD7) and imaged under magnification. Cell motion was quantified with or without ultrasound insonation. The acoustic radiation force (ARF) acting on a cell-MB pair was modeled by assuming the driving force is associated with the MB, and the viscous drag is due to the larger cell. A separate observation of cell-MB rotation caused by the ARF was explained by considering the torque on the cell, where adherent MBs act as point forces. Under insonation, tagged cells were observed to rotate to align with the ARF, and to move in the direction of the ARF. If a tagged cell was adherent to the coverslip, it only rotated. The model for rotation-only behavior fit well with the data. Under flow, tagged leukemia cells were deflected by ultrasound, while erythrocytes were unaffected. These initial studies suggest a new way for isolating and sorting cells. [Funded by LSDF #3292512, RBBR 17-02-00261, NIH P01 DK43881, and NSBRI via NASA NCC 9-58.]