P117-139–specific CTL lyse WT1-positive tumor cells.

Three weeks after the third immunization, spleen cells of mice that had been inoculated with the peptides p235-243 or p117-139 were stimulated in vitro with the relevant peptide and tested for their ability to lyse targets incubated with WT1 peptides and WT1-positive and -negative tumor cells. Bars represent the mean percentage specific lysis and standard deviations in chromium release assays performed in triplicate with effector:target (E:T) ratios of 25:1, 5:1, and 1:1. (A) Cytotoxic activity of the p235-243–specific T-cell line against the WT1-negative cell line EL-4 (EL-4, WT1 negative); EL-4 pulsed with the relevant (used for immunization and for restimulation) peptide p235-243 (EL-4 + p235-243); EL-4 pulsed with the irrelevant peptides p117-139 (EL-4 + p117-139), p126-134 (EL-4 + p126-134) or p130-138 (EL-4 + p130-138), and the WT1-positive tumor cells BLKSV40 (BLKSV40, WT1 positive) and TRAMP-C (TRAMP-C, WT1 positive). (B) Cytotoxic activity of the p117-139 specific T-cell line against EL-4; EL-4 pulsed with the relevant peptide P117-139 (EL-4 + p117-139) and EL-4 pulsed with the irrelevant peptides p123-131 (EL-4 + p123-131), or p128-136 (EL-4 + p128-136); BLKSV40 and TRAMP-C.