Effect of CD33 expression on AMG 330-induced cytotoxicity. (A) Parental OCI-AML3 and (B) parental KG-1a cells were transduced with wild-type CD33 to generate sublines that expressed CD33 at different levels, as indicated by arbitrary median fluorescence units. Parental cells and corresponding sublines were incubated with increasing concentrations of AMG 330 and various E:T cell ratios using healthy donor T cells. After 48 hours, cell counts were determined and cytotoxicity was assessed with DAPI staining to quantify drug-specific cytotoxicity. Results (mean ± SEM) are shown as from 4 independent experiments (for quantification of CD33 expression) or from 3 independent experiments performed in duplicate wells using a single healthy donor as source for exogenous T cells (for determination of specific cytotoxicity; qualitatively similar results were obtained with T cells from 2 other healthy donors).