A bacterially expressed particulate hepatitis E vaccine: antigenicity, immunogenicity and protectivity on primates

It was evaluated its antigenicity, immunogenicity and efficacy of a candidate recombinant hepatitis E virus (HEV) vaccine, referred hitherto as HEV 239 vaccine. The vaccine peptide has a 26 amino acids extension from the N terminal of another peptide, E2, of the HEV capsid protein, which has been shown to protect monkeys against HEV infection previously. The vaccine peptide is similar as E2 in that: first, the vaccine peptide migrates predominantly as dimer in SDS-PAGE and it is dissociated into monomers by heating; second, its dimeric form of which predominantly recognized by HEV reactive human serum; and third, it shows the same pattern of reaction as E2 with a panel of eight monoclonal antibodies that had been raised against E2. In contrast to E2, the vaccine peptide aggregates to form particles of 13 nm mean radius, and consequently, it is more than 240 times more immunogenic than E2. Using alum as adjuvant, immunizing dose determined in mice was 80-250 ng for the vaccine and >60 microg for E2. Rhesus monkeys twice vaccinated with a 10 microg or a 20 microg formulation of this vaccine showed essentially the same antibody response, whereas the response to a 5 microg formulation was delayed but reached similar antibody levels. All the three vaccine formulations afford complete protection against infection with 10(4) genome equivalent dose of the homologous genotype 1 virus. At higher virus dose of 10(7), the same vaccine formulation partially protected against the infection and completely protected against hepatitis. The efficacy of the vaccine was essentially the same for the homologous genotype 1 virus and heterologous genotype 4 virus.