Bystander help within a polyepitope DNA vaccine improves immune responses to influenza antigens.

A polyepitope DNA vaccine has the potential to generate protective immune responses to a range of antigens in a single construct. We investigated whether it was possible to obtain responses to individual epitopes from different antigens, directly linked in a string, and whether the response to a given epitope was enhanced by adjacent epitopes within the construct. A polyepitope plasmid was created, which included three Th epitopes (influenza haemagglutinin, moth cytochrome c and ovalbumin), a Tc epitope (ovalbumin) and two B cell epitopes (haemagglutinin and ovalbumin). Mice were immunized with DNA by using a gene gun. Responses to the polyepitope DNA vaccine were compared with those to DNA vaccine comprising only the haemagglutinin Th and B epitopes (HAT(h)B) or with responses to the recombinant protein. These experiments showed that the polyepitope DNA vaccine induced greater antigen-specific responses to HAT(h)B peptide than the HAT(h)B DNA vaccine. Antigen-specific in vivo cytotoxic responses following polyepitope DNA vaccination were also clearly demonstrable. We conclude that a 'naked DNA' polyepitope vaccine generates specific responses to constituent epitopes and that adjacent irrelevant epitopes may enhance these responses.