FOLR1 is uniquely expressed in CBF/GLIS AML, and FOLR1-expressing AML is sensitive to STRO-002, a FOLR1-directed ADC. (A) Box/violin plot of FOLR1 transcript expression in CBF/GLIS AML (N = 38), DEK-NUP214 (N = 48), ETV6-MNX1 (N = 16), NPM1-MLF1 (N = 8), NUP98-KDM5A (N = 32), NUP98-NSD1 (N = 104), RBM15-MKL1 (N = 10), other AML (N = 1235), normal peripheral blood CD34⁺ samples (N = 16), and normal bone marrow samples (N = 68) from TARGET Pediatric AML study. (B,D,F) Flow cytometric analysis of FOLR1 cell surface expression on MV4;11 parental cells and MV4;11 cells transduced with FOLR1 expression construct (MV4;11 FOLR1⁺), CBF/GLIS-transduced CB hematopoietic stem/progenitor cells (HSPCs) and WSU-AML cells, respectively. The FOLR1 mean fluorescent intensity (MFI) vs isotype is shown at the bottom of the histogram. (C,E,G) In vitro cytotoxicity of STRO-002 against MV4;11 and MV4;11 FOLR1⁺, CBF/GLIS-transduced cord blood (CB) HSPCs and WSU-AML cells, respectively. Cells were treated with increasing doses of STRO-002 alone or in excess of naked antibody SP8166 (1 uM). After 3 days of continuous exposure, viability was assessed by Cell Titer-Glo assay. Data are normalized to untreated controls. Error bars denote standard deviation from 2 technical replicates at each dose. Max, maximum; NBM, normal bone marrow; TPM, Transcripts per million.