Autologous dendritic cells are transduced ex vivo with an adenoviral vector encoding the HER2 extracellular and transmembrane domains, enabling the DCs to express, process, and present HER2 antigens on MHC I and II with costimulation. After administration, these DCs prime and expand HER2-specific CD8+ cytotoxic T cells and CD4+ helper T cells and can induce anti-HER2 antibodies, generating tumor-specific immunity against HER2-positive cancers.