IL-2 expression in parental or IL-2 gene–transduced and selected NK cell lines. (A) and (B) Nonpermeabilized or permeabilized cells, respectively, were stained with the FITC-labeled antibody for IL-2 and examined for surface or intracytoplasmic expression of IL-2 by flow cytometry. One representative experiment of 3 performed is shown for YT cells. Similar data were obtained in 3 experiments performed on NK-92 cells. (C) Immunostaining for IL-2 in stably transduced and selected NK-92 cells (original magnification ×1,000).