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). A recent study suggested that ORF2 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 but is not sufficient for functional research. A more rapid and productive method for yielding ORF2 could help to study its antigenicity and immunogenicity. In this study, the ORF2 (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 (tPA) was used to study antigenicity and immunogenicity. Indirect ELISA revealed that ORF2 (tPA) was not antigenically identical to HEV 239 antigen (p239). The ORF2-specific antibodies were successfully induced in one-dose-vaccinated BALB/c mice. The ORF2-specific antibody response was detected in plasma from HEV-infected patients. Recombinant ORF2 (tPA) can act as a decoy to against B cells. Altogether, our study presents a design strategy for ORF2 expression and indicates that ORF2 (tPA) can be used for functional and structural studies of the HEV life cycle.