Figure 3.

Vaccination with ligand-expressing tumor cells confers specific immunity to the corresponding ligand-negative tumor cells. a, B6 mice that had previously rejected ligand-transduced tumor cells (5×10⁶ EL4, 1×10⁴ B16-BL6 or 1×10⁴ RMA transductants) were inoculated subcutaneously with control-transduced tumor cells of the same type (EL4: 5×10⁶ ; B16-BL6: 1×10⁴ ; RMA: 1×10⁵). Primary exposure occurred 8-12 weeks before challenge. b, B6 mice that had been vaccinated 12 weeks earlier with each ligand-transduced tumor cell type were injected with the same or different ligand-negative cell lines. The primary and secondary tumor doses were as in (a). c, Depletion of CD8⁺ cells during the primary challenge prevents development of immunity. Rechallenge with control-transduced tumor cells occurred 8-12 weeks after vaccination. Naïve B6 mice were challenged in parallel. d, B6 mice were injected with PBS or were vaccinated with 5×10⁶ irradiated or 1×10⁴ living transduced or untransduced B16-BL6 tumor cells. Mice were challenged 10 days later with 10⁴ untransduced B16-BL6 cells in the opposite flank. Data are representative of two experiments.