DNA inoculation with a plasmid vector carrying the hepatitis E virus structural protein gene induces immune response in mice

The plasmid construct, pJHEV, containing the full-length open reading frame 2 (ORF-2) of hepatitis E virus (HEV) gene, expresses the HEV structural protein ORF-2 in Cos-7 cells under the control of a hCMV promoter. No ORF-2 protein could be detected in Cos-7 cells transfected with either vector alone or with a vector containing the ORF-2 of HEV in the incorrect orientation. The successful construct was further tested in BALB/c (H-2d) mice for the induction of an ORF-2 specific immune response. Intramuscular (i.m.) immunization of mice pretreated 24 h earlier with bupivacaine with the naked DNA construct elicited a humoral immune response in 80% and 100% of two separate groups of mice, respectively. No anti-ORF-2 responses were observed in mice immunized with the vector only. Sera from mice injected with pJHEV specifically recognized HEV ORF-2 structural protein expressed in recombinant baculovirus in an enzyme-linked-immunosorbent assay (ELISA) and Western blot, Anti-ORF-2 serum titers peaked at ca 1:5000 in the ELISA and 1:1000 in the Western blot. These titers have remained constant for over 12 months after the last boost of pJHEV. To our knowledge, this is the first report of the use of DNA-based immunization for the generation of an immune response to a HEV structural protein.