Fine specificity of the Gag-specific CTL response. CTL lines of P1 (a and b), P2 (c and d), and P11 (e and f) were tested against autologous target cells pulsed with peptide mixtures (a, c, and e) or individual peptides selected from the responding mixtures (b, d, and f). The concentration of the peptides used for sensitized target cells was always 1 μM; the E/T ratio was 10:1.