Drug-induced CD33 modulation. After exposure to a bivalent CD33 antibody (P67.6) or AMG 330 for 48 hours, CD33 cell-surface expression was quantified on ML-1, NB4, and TF-1 cells and compared with that of corresponding untreated control cells. Results are shown as a percentage of expression (mean ± SEM) relative to control cells from 3 independent experiments.