Immunogenicity difference between two hepatitis E vaccines derived from genotype 1 and 4.

We investigated the immunogenicity difference between hepatitis E vaccine p239 derived from hepatitis E virus (HEV) genotype 1 and vaccine p179 derived from HEV genotype 4; and the presence of genotype-specific neutralizing epitopes. HEV ORF2 recombinant proteins (p166W01, p166Mex, p166US and p166Chn) derived from the four HEV genotypes were used to detect anti-HEV IgGs in sera of mice and humans vaccinated with p179 or p239 and in sera of rhesus monkey challenged with HEV genotype 1 or 4 strains. Then monoclonal antibodies (mAbs) against genotype 1 or 4 ORF2 recombinant proteins were prepared and their immunoreactivity was assessed using ELISA and Western blotting; their neutralizing activity was evaluated by an in vitro PCR-based neutralization assay. The results revealed significant immunogenicity difference between the two vaccines: p239-induced IgGs reacted more strongly against p166W01 and p166Mex than against p166US and p166Chn in mice and humans. By contrast, p179-induced IgGs showed a stronger reactivity against p166US and p166Chn than against p166W01 and p166Mex. This difference has also been observed in the sera of rhesus monkeys challenged with HEV genotype 1 or 4 strains. Moreover, besides the two common neutralizing mAbs 3G1 and 5G5, two genotype-specific neutralizing mAbs, 2B1 and 4C5, were obtained. 2B1 could specifically bind to recombinant proteins derived from genotypes 1 and 2 and neutralized only genotypes 1 and 2 strains, while 4C5 immunoreacted specifically against recombinant proteins derived from genotypes 3 and 4 and neutralized only genotypes 3 and 4 strains. These findings revealed the existence of immunogenicity difference between the p179 and p239 vaccines and demonstrated that this difference could be due to the presence of HEV genotype-specific neutralization epitopes.