To test our hypothesis whether Exo-CD19 CAR was able to target and have a cytotoxic effect on CD19-positive leukemia B-cells or not, we chose two types of target cells, namely CD19-negative control cells (HL-60 and K-562) and CD19-positive target leukemia cells (JM1, Sup-B15, REH, NALM-6). Here, CD19 is linked to leukemia.