Human Her-2 DNA Vaccines Containing Heterologous Rat Neu Sequence Overcome Immune Tolerance to Induce Elevated Antitumor Immunity

To overcome immune tolerance to Her-2, DNA vaccines have been formulated to express both human Her-2 and heterologous rat Neu in separate plasmids or as single hybrid constructs to encode Her-2 and neu fusion proteins: pE2-Neu TM (Her-2 codons 1-390 with neu codons 391-688), pE2-Neu 500TM (Her-2 1-390, neu 391-500, and Her-2 500-687), or pNeu-E2 TM (neu 1-390 with Her-2 391-687). Candidate vaccines were tested in Her-2 transgenic (Tg) mice of BALB/c (BALB), (BALB/c x C57BL/6) F1 (F1), or C57BL/6 (B6) background, with decreasing intrinsic immune responsiveness to Her-2. The cocktail vaccine or hybrid pE2-Neu TM was much more effective than self pE2 TM (Her-2 codons 1-687) in antibody induction. Heterologous pNeu TM and hybrid pE2-Neu TM were more effective than self pE2 TM in activating Her-2-specific IFN-γ-producing T cells. In all test strains, pE2-Neu TM showed the highest level of anti-Her-2 immunity to protect mice from tumor challenge. pE2-Neu 500TM , with an abbreviated neu substitution, or the reverse construct, pNeu-E2 TM , were less effective, indicating the requirement of particular Her-2 and neu sequences for priming immune effector cells in Her-2 Tg mice. In B6 Her-2 Tg mice, rejection of Her-2-positive tumors protected mice from Her-2 negative tumors, showing epitope spreading. With one preventive and three therapeutic vaccinations, D2F2/E2 tumor was rejected in five of seven and seven of eight BALB Her-2 Tg mice that received pE2 TM and pE2-Neu TM , respectively, and pE2-Neu TM induced higher levels of Her-2 antibodies. The strategy of incorporating heterologous antigen with self-antigens resulted in a potent Her-2 DNA vaccine and may be applicable to other tumor-associated antigens.