Cell cytotoxicity of DT388–GM-CSF on TF1 human leukemia cells. Cells were exposed at the dilutions indicated for 48 hours at 37°C/5% CO₂ . Incorporation of ³H-leucine was assayed after an additional 4 hours incubation and compared against untreated cell incorporation. The percent apoptotic nuclei based on DAPI staining were determined after 48 hours for different dilutions of DT388-GMCSF. (•) % maximal protein synthesis; (▪) % apoptosis.