Recombinant adenoviruses expressing the extracellular (EC) and transmembrane (TM) domains of human HER2 (HER2ECTM) are described. The recombinant adenoviruses express a chimeric fiber protein having the adenovirus type 35 (Ad5) shaft and knob domains, which facilitates transduction of human dendritic cells by the recombinant HER2ECTM expressing adenovirus. Compositions that include dendritic cells transduced by the recombinant adenovirus and their use for treating HER-positive tumors is described.