Response of different leukemic cell lines to GO in vitro. (A-B) Exponentially growing AML cell lines were plated in the presence or absence of increasing concentrations of GO or of the unconjugated parent antibody hP67.6. ³H thymidine uptake (A) and cell viability (B) were measured at 48 to 60 hours. THP-1 ± GO is indicated by ○; NB-4 ± GO, □; KG-1 ± GO, ▪; HL-60 ± GO, ♦; HL-60 ± hP67.6, ⋄. (C) The B-cell line MEC-2 was also tested for ³H-thymidine uptake (▵) and cell viability (▴) in the same experimental conditions. The results are the mean and standard deviations of triplicate wells and are representative of at least 3 independent experiments.