CD19-DE is efficient in a preclinical phase 2–like xenograft trial of MLL-rearranged BCP-ALL. (A) Experimental scheme. Patient-derived ALL xenografts were established by orthotopic intrafemoral transplantation of 100 ALL cells per animal from 13 patients (Table 1) into 2 NSG mice each (day 0). Mice were randomized into control or CD19-DE (treatment) groups. The antibody was injected intraperitoneally (1 mg/kg) on days +1, +3, +6, +10, +13, and every 21 days thereafter. (B, C) Reduction of human ALL blast counts in the peripheral blood of xenografted mice by treatment with antibody CD19-DE: pooled analysis, Mann-Whitney U test (B); individual analysis (C). Note that in case of patient 6, the control mouse had already been sacrificed before day +44, and the treatment mouse was still alive. (D) Survival prolongation of mice xenografted with ALL blasts from 13 different patients by treatment with antibody CD19-DE in the preclinical phase 2–like study (Kaplan-Meier log-rank test). (E) Percentage of human blasts in the bone marrow and spleens of all animals at the time of euthanasia. n/a, not applicable (postmortem changes precluded this analysis); Sp, spleen. *Patients with a >2-fold difference in peripheral blasts in control versus treatment mice.