We first tested anti-leukemia activity of UCART123 against leukemia cell lines (Fig. 1b and Supplementary Fig. 1a) and found specific cytotoxicity against a CD123-positive AML cell lines (MOLM13, THP1, KG-1, Kasumi-6, and MV4;11) but not against a CD123-negative cell line (Jurkat). Here, IL3RA is linked to leukemia.