aAPC-mediated expansion of mHag-specific polyclonal CTL lines. Polyclonal CTL lines 4 and 5 were stimulated with aAPCs and either autologous CD4⁺Th cells (CTL line no. 4) or autologous PBMCs (CTL line no. 5) in the presence of 20 U/mL IL-2 and 10 ng/mL IL-7. Responder-stimulator ratios were as follows: CTLs/aAPCs/PBMCs, 1:1:1; CTLs/aAPCs/CD4⁺Th, 2:2:1. Prior to each restimulation, HA-1^A2 tetramer staining of viable CD8⁺ T lymphocytes and cytotoxicity assays were performed. Cytotoxicity results are shown for an effector-target ratio of 10:1. The percentages in the scatterplot subpanels represent the percentage of viable CD8⁺ HA-A1^A2 tetramer–positive lymphocytes in the total population of viable CD8⁺ lymphocytes.