Fig. 1.

Vaccination with yeast-CEA induces antigen-specific T-cell responses. CEA-Tg mice were vaccinated with 0.1 YU control yeast or yeast-CEA on days 0 and 7. On day 21, mice were sacrificed, spleens were harvested, and splenocytes were used for assays. A, CD4⁺ cell proliferation. Purified CD4⁺ T cells were cultured with irradiated APCs and CEA protein for 5 days. ³H-thymidine (1 µCi/well) was added to the wells for the last 24 h, and proliferation was assayed by measuring incorporated radioactivity. Open squares, control yeast. Closed circles, yeast-CEA. B, CD8⁺ CTL activity after vaccination with yeast-CEA. Splenocytes were stimulated with CEA_572–579 peptide for 6 days before assays. 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. SD is based on the mean of triplicate wells. Open circles, CTL activity directed against EL-4 cells pulsed with VSV-NP peptide. Closed circles, CTL activity directed against EL-4 cells pulsed with CEA peptide. C, CD8⁺ CTL activity after vaccination with control yeast. Open squares, CTL activity directed against EL-4 cells pulsed with VSV-NP peptide. Closed squares, CTL activity directed against EL-4 cells pulsed with CEA peptide. C (Insert), CD8⁺ CTL activity against tumor cells after vaccination with yeast-CEA. Splenocytes were stimulated with CEA_572–579 peptide as above. Lymphocytes were incubated for 5 h with ⁵¹Cr-labeled target MC38-CEA⁺ (closed bars), at an E:T ratio of 100:1. As a negative control, splenocytes from mice receiving PBS (vehicle control) were stimulated with CEA peptide as above and CTL activity directed against MC38-CEA⁺ tumor cells (open bars).