Epratuzumab-induced reduction of select surface antigens on normal B cells. Fresh PBMCs isolated from the blood of healthy donors were treated overnight with 10 µg/mL epratuzumab or a nonbinding isotype control monoclonal antibody (mAb; labetuzumab, humanized anti-CEACAM5 IgG1κ), and the relative surface levels of selected proteins on B cells were measured using triplicate samples by flow cytometry. (A) Survey of the effect of epratuzumab on 13 different B-cell antigens. The number of donors evaluated for each specific antigen is indicated in parentheses. The levels of the key proteins were measured in 7 to 19 independent experiments. Bar represents mean values. (B) Reduction of CD19 on CD27⁺ and CD27^– B cells. Results are from 3 independent experiments using 3 different healthy donors (N1, N2, and N3). (C) Comparison of the reduction of CD19 and CD21 on B cells following 2-hour vs overnight treatment. The number of donors evaluated for each antigen/time is indicated within the bars. Each plot is shown as the % MFI of the isotype control treatment. Each donor sample was evaluated in triplicate. Error bars represent standard deviation (SD).