The growth-inhibitory effect is specific to CD19, but not restricted to myeloma cells. (A) The expression vectors pCI-CD19 and pCI-▵19 were electroporated into the human myeloma cell line, U-266, to generate U-19⁺ and U-19 cells, respectively, as detected by flow cytometry after staining with PE-labeled anti-CD19 (top). Cells expressing surface CD19 were sorted after 2 weeks of selection in G-418 (1 mg/mL) and used for evaluation of growth pattern (bottom). Data are from 3 independent experiments. The mean ± SD of cell number at each time is shown. (B) The pCI-CD19 and pCI-▵19 vectors were transfected by lipofection into the human erythroleukemia cell line, K-562, to generate K562-19⁺and K562-19, respectively. After 2 weeks of selection in G-418 (1 mg/mL), surface CD19 expression was confirmed by flow cytometry after staining with PE-labeled anti-CD19 (top), and the in vitro growth curve of these cells is shown as mean ± SD values of cell numbers at the indicated time points (bottom).