P495-specific CTLs remain highly cytotoxic after purification using tetramer and anti-PE microbeads. (A) Tetramer reactivity and cytotoxicity profile of P495-depleted CTL fraction (P495^-) after restimulation on AAPC^A2pp65. CTLs are less than 0.5% P495 tetramer-positive (top panel). Cytotoxicity assays were performed starting from an E/T ratio of 80:1 against T2 cells (middle panel) or against A2.1⁺ BLCLs (bottom panel). In the middle panel, ▪ indicates T2 cells pulsed with P495; and ♦, T2 cells pulsed with flu. In the bottom panel, ▪ indicates BLCL^pp65; ♦, BLCL^flu. (B) Tetramer reactivity and cytotoxicity profile of P495-specific CTL fraction (P495⁺) after restimulation on AAPC^A2pp65. P495⁺ CTLs remain more than 95% P495 tetramer-positive (top panel). Cytotoxicity assays were performed starting from an E/T ratio of 5:1 against the same targets as in panel A. CTLs specifically killed T2 cells pulsed with P495 (middle panel) and BLCL^pp65 (bottom panel). Similar results were obtained with T cells of 3 different donors.