A plasmid
DNA was constructed to encode the N-terminal 505 aa of human ErbB-2 (E2, HER-2/neu) and designated as secreted ErbB-2 (secE2). Recombinant secE2
protein was detected in the transfected cells and was secreted as an 80-kDa
glycoprotein. Vaccination of BALB/c mice with secE2
DNA induced both
IgG1 and
IgG2a ErbB-2-specific Abs and protected approximately 90% of mice against mouse mammary
tumor D2F2, which expressed human ErbB-2 (D2F2/E2). The efficacy of secE2
vaccine was comparable with that of wild-type ErbB-2
DNA, which encodes the entire 1258 aa of ErbB-2
protein, induced only
IgG2a E2-specific Abs, and stimulated greater CTL activity. Immune lymphocytes were stimulated in vitro with irradiated 3T3 cells, which expressed ErbB-2, K(d), and B7.1. CTL activity was measured by the lysis of E2-positive target cells and by intracellular IFN-gamma production. To enhance CTL activation, mice were immunized with a combination of secE2 and cytoplasmic E2 (cytE2); the latter encodes the 1258-aa ErbB-2
protein that was released into the cytoplasm upon synthesis. Significant increase in CTL activity was demonstrated after mice were immunized with the
combined vaccines and all mice were protected from D2F2/E2
tumor growth. Therefore, secE2, which induced Th2 Ab and weak CTL, conferred similar protection as E2, which induced Th1 Ab and strong CTL. Combined vaccination with secE2 and cytE2 resulted in Th2 Ab, strong CTL, and the most effective protection against
tumor growth. The strategy of coimmunization with
DNA that direct Ags to different subcellular compartments may be adapted as appropriate to optimize immune outcome.