Kinetics of PS exposure on activated human CTLs. (A) T2 cells were loaded with different concentrations of Melan-A peptide and used as stimulator cells for Melan-A–specific CTLs. At indicated time points CTLs were harvested, stained with PE-conjugated Melan-A–MHC tetramers, CD8-APC, annV-FITC, and PI.. PI^–CD8⁺ CTLs were gated and analyzed for annV-FITC binding by flow cytometry. Mean fluorescence intensity (MFI) of one representative experiment of 3 is shown. (B) CTLs were stimulated with peptide-loaded (5 μg/mL) T2 cells or peptide-loaded (30 μg/mL) mature DCs. One representative kinetics of 3 is shown. (C) Melan-A–specific CTLs were labeled with the membrane dye PKH-26, stimulated for 3 hours with Melan-A–loaded T2 cells and isolated by cell sorting. Sorted CTLs were then cultured in TCGF-containing medium and PS exposure was determined by staining with annV-FITC at different time points.