Her-2/neu is a well-characterized tumor-associated antigen, the overexpression of which in human carcinomas correlates with a poor prognosis. Here, we evaluated Her-2/neu-specific humoral and cellular immune responses in immunized monkeys after immunization with nonreplicating adenovirus (AdHM) expressing the extracellular and transmembrane domain of human Her-2/neu (HM) and/or naked DNA vaccine (pHM-hGM-CSF) expressing human granulocyte-macrophage colony-stimulating factor together with HM. Priming of monkeys with AdHM generated Her-2/neu-specific long-lasting antibody production. Furthermore, these Her-2/neu-specific antibodies produced by AdHM immunization, some of which shared epitope specificity with Herceptin, were able to induce antibody-dependent cellular cytotoxicity against Her-2-expressing target cells. Cellular immune responses were elicited in all monkeys immunized with Her-2/neu-expressing vaccine; interferon-gamma was secreted when these splenocytes were restimulated with Her-2/neu-expressing autologous cells, and immunization with AdHM induced Her-2/neu-specific lymphoproliferative responses. Further, immunization with pHM-hGM-CSF before AdHM immunization noticeably enhanced cytotoxic T-lymphocyte activity. In addition, we observed no abnormalities that would indicate that the genetic vaccines had toxic effects in the immunized monkeys. Thus, we can conclude that our genetic vaccines efficiently elicited Her-2/neu-specific humoral and cellular immune responses without causing severe adverse effects in nonhuman primates and that as such they warrant further clinical investigation.