In order to further increase antigenicity to provide a DNA vaccine which is clinically usable in humans, the inventors of the present invention focused on exosomes, which are garnering attention as tools for DDS, and discovered that an exosome expressing a fusion antigen of an exosome (extracellular microparticle)-constituent protein and a vaccine antigen has excellent cytotoxic T-cell inducibility. Consequently, the present invention provides a nucleic acid constituent including a nucleic acid sequence coding for an exosome marker protein and a nucleic acid sequence coding for a vaccine antigen.
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