Alemtuzumab-induced death in human ATL cells in vitro. Primary ATL cells from the patient described in this report (ATL-1) (▪) and from a previous patient with acute ATL (ATL-2) (□) were incubated for 4 hours in media with alemtuzumab and anti-Fc IgG (both 10 μg/mL) (direct apoptosis), alemtuzumab (10 μg/mL) with PBMCs at an effector-target ratio of 25:1 (ADCC), or alemtuzumab (10 μg/mL) in media with 30% human serum (CDC). Cell death was determined by propidum iodide staining with FACS analysis for direct apoptosis and CDC, or a chromium-51 release assay for ADCC. ATL-2 cells carried a mutated TP53 gene. Experiments were done in triplicate, and results are expressed as average. Bar height reflects the average percentage of dead cells as compared with untreated control values.