CD19-DE is efficient in an MRD-model of infant BCP-ALL in NSG mice. (A) Establishment of the MRD model: 6 NSG mice per group were injected with 10, 50, 100, or 500 cells from patient 1 in Table 1. Mice were sacrificed upon leukemia development or after 1 year at the latest. The percentage of engrafted animals was determined. (B) Experimental scheme. Patient-derived ALL xenografts were established by orthotopic intrafemoral injection of 100 ALL cells per animal in NSG mice (day 0). The antibody was injected intraperitoneally (1 mg/kg) on days +1, +3, +6, +10, +13, and every 21 days thereafter. (C) Reduction of human ALL blast counts in the peripheral blood of mice xenografted with leukemic cells from patients 1 and 2 by treatment with antibody CD19-DE (Mann-Whitney U test); control mice were left untreated; n = 8 in the control group, and n = 7 in the treatment group. Human blast percentages were determined by 2-color flow cytometry using antibodies specific for human CD19 or CD45 antigens. (D) Reduction of human ALL blast counts in the peripheral blood of mice xenografted with leukemic cells from patients 3 and 4 by CD19-DE (Mann-Whitney U test); control mice received trastuzumab or trastuzumab-DE, as indicated; n = 7 in all groups. (E, F) Survival prolongation in xenografted mice by CD19-DE in patients 1 and 2 (E) and patients 3 and 4 (F) (Kaplan-Meier log-rank test). FACS, fluorescence-activated cell sorting; n.s., not significant.