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.