Reduction in cytokine-induced apoptosis by TGF-β. Purified CD3⁻CD56⁺ human NK cells were cultured for 3 days in medium containing (A) 15 ng/mL IL-2, (B) IL-2 and 3 ng/mL IL-12, or (C) IL-2, IL-12 and 2 ng/mL TGF-β₂ . Nuclei were stained with PI and then quantitated for apoptosis by flow cytometry. Results are representative of three independent experiments.