Effect of CD33 expression on GO-induced cytotoxicity. Parental (A) 32D, (B) OCI-AML3, and (C) KG-1a cells and their sublines that were transduced with wild-type CD33 and expressed CD33 at different levels, as indicated by arbitrary fluorescence units, were incubated with various concentrations of GO for 3 days, before cytotoxicity was assessed with PI staining. In the case of KG-1a sublines, cells were cotreated with CSA. Increases in the percentage of PI-positive cells in GO-treated cells are compared with corresponding cells that were incubated without GO, and results are shown as mean ± SEM from 2 to 4 independent experiments performed in duplicate or quadruplicate wells.