IMGN529 specifically depletes normal and malignant human B cells. (A) Histogram of human CD19⁺ B cells stained with anti-CD37-PE and anti-CD20-PE antibodies. (B) CD37 and CD20 expression levels in blood cells from healthy donors by quantitative flow cytometry (BD QuantiBRITE). Average values from 4 donors are plotted as ABC for B cells (CD19⁺), T cells (CD3⁺), NK cells (CD56⁺), monocytes (CD14⁺), and granulocytes (CD66abce⁺). (C) In vitro depletion of human blood cells after 1-hour incubation with 10 μg/mL of indicated compounds from purified PBMCs or (D) whole-blood samples derived from 5 healthy donors. (E) Dose-response curves for depletion of B cells (■) and T cells (○) from PBMCs treated with IMGN529. (F) In vitro depletion of CD19⁺CD5⁺ malignant B cells in PBMCs from 4 patients with CLL after 1-hour incubation with 10 μg/mL of indicated compounds (mean ± standard error of the mean is shown). (G) Histogram of CD19⁺CD5⁺ malignant B cells in PBMCs from a representative patient with CLL stained with anti-CD37-PE (solid line) and anti-CD20-PE (dashed line) antibodies compared with an isotype control (shaded).