Tetramer reactivity and cytotoxicity profile of CTLs activated on HLAA2.1/AAPCs. (A) Staining with anti-CD8 (FITC-labeled, x-axis) and HLAA2.1/P495 tetramer (PE-labeled, y-axis). (B) Cytotoxicity assays performed against peptide-pulsed TAP-deficient A2.1⁺ T2 targets with CTLs shown above. ▪ indicates T2 cells pulsed with P495; ♦, T2 cells pulsed with irrelevant peptide. Left panels: CTLs cultured on “empty” AAPCs. Staining with P495 tetramer was lower than 0.1%. Middle panels: CTLs activated on AAPC^A2P495. Right panels: CTLs activated on AAPC^A2pp65. AAPC^A2P495 and AAPC^A2pp65 efficiently kill T2 targets pulsed with P495. Cytolysis at a given E/T ratio is higher for CTLs activated on AAPC^A2pp65 compared with AAPC^A2P495. Results are representative for 3 different donors.