Development of immunogenic recombinant Oka varicella vaccine expressing hepatitis B virus surface antigen

Recombinant Oka varicella vaccine expressing hepatitis B virus (HBV) surface antigen (HBs) was constructed by inserting the HBs gene into the viral thymidine kinase (TK) gene and was examined for its immunogenicity in guinea-pigs. The HBs gene encoding 25 amino acids of preS2 and the whole of the S region was inserted into the TK gene of the cloned plasmid. The chimeric plasmid DNA and Oka varicella vaccine DNA were cotransfected and recombinant virus was isolated after immunofluorescence screening using a monoclonal antibody to HBs and a fluorescein-conjugated anti-mouse antibody. Expression of viral HBs was detected in the cytoplasm of infected cells and was stable over several repeated passages in vitro. The recombinant virus expressed 26K and 30K HBs molecules in infected cells and the culture supernatant contained 30K and 35K HBs molecules. HBs was purified at a density of 1.20 g/ml from the culture supernatants. The recombinant virus induced an antibody response to HBs as well as to varicella-zoster virus (VZV) in guinea-pigs, and the antibody titre to HBs was comparable to that induced by a recombinant HBs subunit vaccine produced in yeast. Thus a single dose of live recombinant Oka varicella vaccine could induce good immunity to VZV and HBs. The recombinant Oka varicella vaccine expressing HBs may be a good candidate for a combined HBV and VZV vaccine.