Immune response elicited by S typhimurium-mediated DNA immunization. (A) CTL-mediated recognition of β-gal–expressing tumor target cells. Splenocyte cells from mice vaccinated with SL7207 (pCMVβ; ▪) or SL7207 (▴) at the indicated time points (arrows) were restimulated in vitro for 5 days in presence of βGP1 peptide. After culture, lymphocytes were tested in a⁵¹Cr-release assay at a 50:1 E/T ratio using P13.1 as target. Results are the mean of triplicates; the percentage of nonspecific lysis of P815⁻ cells has been subtracted. (B) Serum IgG levels were measured in antigen-capture ELISA: (▪) β-gal–reactive IgG; (○) ovalbumin-reactive IgG. Results are from sera pools of 3 mice each.