Mean fluorescence intensity of CSFE-labeled BMLF1- and pp65-specific CD8⁺ T cells at day 5 of culture. CD3-activated cells were labeled at day 3 of culture with CSFE and cultured until day 5. Co cells were then stained with BMLF1 or pp65 tetramers. Data indicate the MFI of CSFE labeling within tetramer⁺ cells from 3 donors.