Figure 1.

T cell engaging bispecific antibody (BsAb) against CD19 lyses acute lymphoblastic leukemia cell line with femtomolar EC50. (A) Schematic view of the IgG-scFv BsAb. (B) NALM6 CD19(+) cells were stained with the T cell-engaging CD19-specific BsAb BC250 or a control BsAb. (C) ATC were cultured with ⁵¹Cr-labeled NALM6 cells (E:T ratio=10) in the presence of different doses of BC250 or a control BsAb for 4 hours. Release of ⁵¹Cr was used as an indicator of cytotoxicity. EC50s were compared using t-test. (D–E) T cell-engaging BsAbs with different affinities for CD19 were tested in a T cell-mediated cytotoxicity assay. NALM6 cells were stained with the same antibodies. The EC50 (from cytotoxicity assays, with comparison between EC50s using ANOVA and multiple comparison analysis) and CD19 mean fluorescence intensity or mean fluorescence intensity (MFI) (from flow cytometry experiments) were plotted against each other. ATC, activated human T cells; ANOVA, analysis of variance.