Although DNA-based cancer vaccines have been successfully tested in mouse models, a major drawback of cancer vaccination still remains, namely that tumour antigens are weak and fail to generate a vigorous immune response in tumour-bearing patients. Genetic technology offers strategies for promoting immune pathways by adding immune-activating genes to the tumour antigen sequence. In this work, we converted a model non-immunogenic antigen into a vaccine by fusing it to domain I of the filamentous bacteriophage coat protein III gene. Vaccination with a DNA construct encoding the domain I fusion generated antigen-specific T helper 1-type cellular immune responses. These results demonstrate that the incorporation of protein III into a DNA vaccine formulation can modulate the gene-mediated immune response and may thus provide a strategy for improving its therapeutic effect.