Substantial expression (≥20% surface expression) as detected by the FLT3 mAb 4G8, the specific antibody clone used for generation of 4G8-SDIE undergoing evaluation for B-ALL treatment in this study, was observed in all three cell lines and in 86% (19 of 22) of the investigated patient samples. Here, FLT3 is linked to acute lymphoblastic leukemia.