FLT3 and leukemia: To evaluate the specific cytotoxicity of FLT3L CAR-T cells, FLT3 expression on several AML cell lines was analyzed by specific fluorescence indices (SFI) using flow cytometry and FLT3-positive (FLT3+) leukemia cell lines MV4-11 (SFI:1.45), MOML13 (SFI:1.77), REH (SFI:2.48), and THP-1 (SFI:1.88) were used as target cells, FLT3-negative (FLT3−) cell line U937 (SFI:1.07) was used as control target cells, and VEC-T cells were used as control effector cells (Fig. 2a).