After preparing a plate of tobacco product-treated PBMCs, as just demonstrated, wash a culture of K562 cells harvested at an 80% confluency in 10 milliliters of DPBS. Resuspend the pellet in 5 milliliters of DPBS, and count the cells. Then, add 1 milliliter of freshly-prepared CFSE working solution to 1 to 2 times 10 to the seventh K562 cells in 1 milliliter of complete medium, and disperse the cell stain by vortexing.
Incubate the cells at room temperature. After exactly 2 minutes, add 200 microliters of FBS, and vortex the cells again, incubating them for another two minutes.
After the second incubation, wash the cells in 10 milliliters of complete medium. Then, resuspend the pellet in another 10 milliliters of complete medium and count the cells. Now, centrifuge the tobacco-treated PBMCs, and decant the supernatant. Then, replace the cover, resuspend the cells by vortexing, and wash them in 200 microliters of complete medium per well.
To initiate the killing assay, add the CFSE-labeled K562 cells to the PBMCs at a 1 to 15 ratio, and incubate the co-culture at 37 degree Celsius and 5% CO2.
After five hours, spin down the cells and discard the supernatant. Resuspend the pellets by vortexing, and then wash the cells with 200 microliters of running buffer per well. Then, add 95 microliters of running buffer followed by 5 microliters of 7-AAD, for a total volume of 100 microliters per well.
Finally, incubate the cells in the dark at room temperature for 15 minutes, then, add 100 microliters of running buffer to each well, and transfer the entire volume to the appropriate corresponding FACS tubes to determine the percentage of 7-AAD and CFSE-positive cells by flow cytometric analysis.
