Autologous B-cell depletion by the DART molecule and dependence on coengagement for T-cell proliferation. (A) The ability of the DART molecules to mediate autologous B-cell depletion was determined by incubating healthy human donor PBMCs with the panel of the indicated proteins for 18 hours and determining the percentage of viable CD20⁺ B cells by FACS. (B) Standard ³H-thymidine proliferation assay using unstimulated primary human PBMCs before (black bars) and after (gray bars) depletion of B cells by immunomagnetic beads. The data are representative of multiple independent experiments using independent healthy human PBMC donors. Phytohemagglutinin (PHA) and IL-2 were used as positive controls for stimulation.