TRAIL-induced apoptosis in IL-2–treated NK cells (10 days) in the presence of 50 ng/mL Actinomycin D (Act D). Act D was administered to the cells at the same time of TRAIL. (A) Negative control was IL-2–treated NK cells + Act D. The percentage of living cells (57.4%) is indicated in the Annexin V^–/PI^– population. (B) IL-2–treated NK cells + TRAIL + Act D. The percentage of living cells (25.9%) is indicated, as well. (C) TRAIL-induced apoptosis in IL-2–stimulated NK cells with or without Act D. Results obtained from 3 unrelated donors are reported. Values are expressed as means ± standard deviation.