Fusion of C3d molecule with neutralization epitope(s) of hepatitis E virus enhances antibody avidity maturation and neutralizing activity following DNA immunization.

Previous studies have identified that a hepatits E virus peptide (HEV-p179), spanning amino acids (aa) 439-617 in the 660-aa protein encoded by open reading frame 2(ORF2) of the Chinese epidemic strain (genotype 4), is the minimal size fragment of conformation-dependent neutralization epitope(s). We report here the successful immunization of mice with DNA vaccines expressing the secreted form of HEV-p179 (fused with a human tissue plasminogen activator (tPA) signal sequence) and the tPA-p179-C3d fusion protein (fused with three tandem copies of the murine complement C3d). Analysis of antibody responses in vaccinated mice revealed that immunizations with tPA-p179-C3d3 DNA vaccine dramatically increased both the level and avidity maturation of antibodies against HEV-p179 compared to p179 and tPA-p179 DNA vaccines. In addition, this increased antibody response correlated with neutralizing titers in a PCR-based cell culture neutralization assay. These results indicate that vaccination with C3d conjugated p179 DNA vaccine enhances antibody responses to HEV, and this approach may be applied to overcome the poor immunogenicity of DNA vaccines to generate HEV neutralizing antibodies.