Cytotoxicity assay
NPC cell lines were labeled with 5 μM CFSE (Sigma, catalog 21888),
seeded in a 96-well plate at 105 cells/well, and T
cells previously cocultured with drug-treated tumor cells (generated as
above) were added at the indicated ratios and cultured for 72 h. Cells
were stained with Fixable Viability Dye eFluor 780 (BD Biosciences), and
staining was evaluated by flow cytometry as described above. The
percentage of specific lysis was then calculated using the following
equation: % specific lysis = 100 x (% specific cell death - % basal
cell death)/100 - % basal cell death. Specific cell death was
determined from viability dye staining of CFSE-positive cells in T cell
coculture wells and basal cell death from wells lacking cocultured T
cells.