Immunodominance of PR2 over PR1 in rVV-EGFP-PR3–immunized mice. (A) Naturally processed PR3 protein was used as Ag for IVS. HHDII mice were immunized with rVV-EGFP-PR3, and splenocytes were expanded for 1 week in culture by stimulation with K562-A2PR3 cells. The cultures were then tested in ICC assays using irrelevant HIV-gag control peptide (i), or with PR1 peptide (ii), or with PR2 peptide (iii) as Ags. The IVS cultures contained PR2-specific CD8⁺ T cells but not PR1-specific CD8⁺ T cells. (B) Induction of PR1-specific CD8⁺ T cells by immunization with vaccinia expressing different proteases. Groups of HHDII mice were immunized with rVV-EGFP-PR3 (i), or with rVV-EGFP-PR3-T (ii), or with rVV-EGFP-HNE (iii). Splenocytes from all 3 groups were expanded by cocultivation with K562-A2 cells loaded with PR1 peptide and after expansion compared in ICC assays using PR1 peptide as Ag. These results are representative of 2 experiments using 3 or 4 mice.