Construction and characterization of a replication-competent human adenovirus type 3-based vector as a live-vaccine candidate and a viral delivery vector

In southern China, as well as in neighboring Asian regions, human adenovirus type 3 (HAdV-3) outbreaks have become very prevalent in recent years. To address this problem regionally and globally, a recombinant virus has been constructed, containing a full-length infectious genomic clone of HAdV-3, to act as a vaccine. This was constructed by using a bacterial homologous recombination mechanism and was based on the cloning, manipulation and maintenance of the full-length adenovirus genome as a stable plasmid in E. coli. The resultant recombinant viral DNA was screened, identified and characterized by duplex PCR, Western blot, indirect immunofluorescence assay and electron microscopy. This putative vaccine strain was shown to be fully infectious in permissive cells, and no genome mutations were found in the recombinant plasmid. To demonstrate the utility of such a vaccine, a recombinant HAdV-3 plasmid expressing the reporter molecule eGFP was also constructed. This confirmed the recombinant protein expression capability. Mice immunized with this recombinant eGFP adenovirus by either intramuscular injection, intragastric or intranasal inoculation routes raised a significant antibody response to eGFP. Our results have provided a solid foundation for development of a recombinant live vaccine and potential more effective adenovirus vector-based delivery system for immune and gene therapy.