Expression of IL-2 mRNA in the parental or IL-2 gene–transduced and selected NK cell lines by QC-RT-PCR. Total RNA extracted from NK cell lines (100 ng from parental cells, 1 ng from IL-2 gene–transduced cells) was reverse-transcribed and amplified using primers specific for IL-2. Southern hybridization was performed with radiolabeled cDNA for IL-2 to confirm the identify of the PCR product. The ratio of cpm in the internal control to cpm in cellular RNA was plotted to calculate the number of copies of IL-2 mRNA/ng total cellular RNA (not shown). (A) NK-92 cells, (B) YT cells.