A Secreted Form of the Hepatitis E Virus ORF2 Protein: Design Strategy, Antigenicity and Immunogenicity

Hepatitis E virus (HEV) is an important public health burden worldwide, causing approximately 20 million infections and 70,000 deaths annually. The viral capsid protein is encoded by open reading frame 2 (ORF2) of the HEV genome. Most ORF2 protein present in body fluids is the glycosylated secreted form of the protein (ORF2^S). A recent study suggested that ORF2^S is not necessary for the HEV life cycle. A previously reported efficient HEV cell culture system can be used to understand the origin and life cycle of ORF2^S but is not sufficient for functional research. A more rapid and productive method for yielding ORF2^S could help to study its antigenicity and immunogenicity. In this study, the ORF2^S (tPA) expression construct was designed as a candidate tool. A set of representative anti-HEV monoclonal antibodies was further used to map the functional antigenic sites in the candidates. ORF2^S (tPA) was used to study antigenicity and immunogenicity. Indirect ELISA revealed that ORF2^S (tPA) was not antigenically identical to HEV 239 antigen (p239). The ORF2^S-specific antibodies were successfully induced in one-dose-vaccinated BALB/c mice. The ORF2^S-specific antibody response was detected in plasma from HEV-infected patients. Recombinant ORF2^S (tPA) can act as a decoy to against B cells. Altogether, our study presents a design strategy for ORF2^S expression and indicates that ORF2^S (tPA) can be used for functional and structural studies of the HEV life cycle.