CD8+ CTL responses after dose escalation of yeast-CEA. CEA-Tg mice were vaccinated with 0, 0.01, 0.1, 1, or 10 YU yeast-CEA twice at 7-day intervals. Fourteen days after the last vaccination, mice were sacrificed, spleens were harvested, and splenocytes were stimulated with CEA peptide for 6 days. Lymphocytes were incubated for 5 h with 51Cr-labeled target EL-4 cells pulsed with CEA or VSV-NP control peptide. Radioactivity in the supernatant was measured and specific lysis calculated. Open circles, EL-4 cells pulsed with VSV-NP peptide. Closed circles, EL-4 cells pulsed with CEA peptide.