STRO-001 therapy demonstrates preclinical efficacy against CD74-positive B-ALL cell lines and primary B-ALL. (A) Flow cytometric analysis of CD74 cell surface expression on REH and RS4;11 B-ALL cell lines. (B) In vitro cytotoxicity of STRO-001 against REH and RS4;11 cells. Experiments were repeated twice (supplemental Figure 4). Data are normalized to untreated controls. Error bars denote standard deviation from 2 or 3 technical replicates at each dose. (C) Top, experimental schema evaluating STRO-001 in vivo efficacy in REH and RS4;11 xenograft models. Bottom, representative images of leukemia burden detected by IVIS imaging in REH and RS4;11 xenograft mice untreated or treated with STRO-001 at 3 mg/kg weekly for 3 weeks. N = 5 mice per group. X indicates death. (D) Quantification of radiance shown in C. N = 5 mice per group. (E) Kaplan-Meier survival curves of REH and RS4;11 xenograft mice untreated or treated with STRO-001. N = 5 per group. Statistical differences in survival were assessed by Log-rank Mantel-Cox test. (F) Flow cytometric analysis of CD74 expression in patient specimen B-ALL-3. (G) Percent B-ALL-3 cells (huCD19⁺) in the bone marrow at indicated weeks following leukemia injection (H) Kaplan-Meier survival curves of PDX B-ALL-3 mice untreated or treated with STRO-001. Data are presented as mean +/− SEM. Statistical differences were determined by unpaired, 2-tailed Student t test. Details of the B-ALL-3 PDX studies (8.5e6 cells/mouse; n = 4 for untreated group, n = 7 for STRO-001-treated group).