IL-2 withdrawal leads to loss of viability and reduced BCL-XL expression in ENKTL cell lines. (A) ENKTL cells cultured in medium lacking IL-2 were assessed over a 120-hour time course by flow cytometry for viability as determined by annexin V plus PI staining. Data were normalized to cell viability of cells grown in medium supplemented with IL-2 and are presented as means ± SD of 3 independent experiments, each performed in triplicates (n = 3). (B) Expression levels of BCL-XL, MCL-1, and BIM proteins were detected by western blot analysis in cells cultured in medium lacking IL-2 (in the presence of the broad-spectrum caspase inhibitor QVD-OPH [25 µM] to prevent late stages of apoptosis with cell demolition) at the indicated time points. Probing for HSP70 was used as a protein loading control. Representative blots are shown.