Comparison of CTLs activated on ER^- PBMCs, BLCLs, AAPC^A2P495 or AAPC^A2pp65. (A) T cells were purified from PBMCs by positive selection using sheep red cell rosetting (SRCR). T cells were used as responders in cocultures with ER^- PBMCs, BLCLs, or AAPCs. All cocultures were started with the same number of responder cells in 24-well tissue-culture plates (1 × 10⁶ T cells/well). IL-2 was added on day 7 to all cocultures and every third day afterward. Cytotoxicity assays and immunophenotyping were performed on days 10 to 14. (B) CD8 and HLA A2.1/P495 tetramer staining on the same day for all cocultures. The percentage of P495-specific CD8 cells in the culture is 20% for ER-PBMCs, 9% for BLCLs, 14% for AAPC^A2P495, and 34% for AAPC^A2pp65. (C) Cytotoxicity assays against T2 targets done on the same day as immunophenotyping (B) are shown for CTLs activated on autologous ER- PBMCs pulsed with P495, autologous BLCLs pulsed with P495, AAPC^A2P495, or AAPCA2pp65. ♦ indicates T2 cells pulsed with flu; ▪, T2 cells pulsed with P495. CTLs activated on ER^- PBMC lyse T2 cells pulsed with P495 but also T2 cells pulsed with flu at the higher E/T ratio. CTLs activated on AAPC^A2pp65 show the highest level of cytolysis of T2 cells pulsed with P495 and very low cytolysis of T2 cells pulsed with flu. Similar results were obtained with 3 different donors.