In vitro characterization of 4G7SDIE and B-lineage acute lymphoblastic leukemia (ALL) blasts. (a) B-lineage ALL blasts (n = 18 patients (black), n = 5 4G7SDIE-treated patients (hatched)) were incubated with murine 4G7 (5 µg/ml), washed and bound antibody was detected by indirect immunofluorescence staining and flow cytometry. CD19 molecules/cell were calculated by comparison with calibrated beads (QIFIKIT). (b) A MCF-7-CD19-transfectant expressing 1.9 × 104 CD19 molecules/cell was incubated with PBMC (n = 12 HVs) and medium, 1 µg/ml of 4G7SDIE or 1 µg/ml χ4G7 and analyzed in xCELLigence assays. (c) B-lineage ALL blasts (n = 5) were incubated with PBMC of one HV (E:T 20:1), autologous serum, medium, and 1 µg/ml 4G7SDIE, respectively. Specific lysis was measured in 2 h-EuTDA assays. (d) ADCC with PBMC (E:T 20:1) from 3 HVs was assessed in xCELLigence assays with 4G7SDIE (2.5 µg/ml) and MCF-7-CD19-transfectants expressing the indicated levels of CD19 molecules/cell. ADCC after 10 hours was depicted and correlation was assessed using Spearman's rank correlation coefficient.