High-Yield Production of Chimeric Hepatitis E Virus-Like Particles Bearing the M2e Influenza Epitope and Receptor Binding Domain of SARS-CoV-2 in Plants Using Viral Vectors

Capsid protein of Hepatitis E virus (HEV) is capable of self-assembly into virus-like particles (VLPs) when expressed in Nicotiana benthamiana plants. Such VLPs could be used as carriers of antigens for vaccine development. In this study, we obtained VLPs based on truncated coat protein of HEV bearing the M2e peptide of Influenza A virus or receptor-binding domain of SARS-CoV-2 spike glycoprotein (RBD). We optimized the immunogenic epitopes' presentation by inserting them into the protruding domain of HEV ORF2 at position Tyr485. The fusion proteins were expressed in Nicotiana benthamiana plants using self-replicating potato virus X (PVX)-based vector. The fusion protein HEV/M2, targeted to the cytosol, was expressed at the level of about 300-400 mu g per gram of fresh leaf tissue and appeared to be soluble. The fusion protein was purified using metal affinity chromatography under native conditions with the final yield about 200 mu g per gram of fresh leaf tissue. The fusion protein HEV/RBD, targeted to the endoplasmic reticulum, was expressed at about 80-100 mu g per gram of fresh leaf tissue; the yield after purification was up to 20 mu g per gram of fresh leaf tissue. The recombinant proteins HEV/M2 and HEV/RBD formed nanosized virus-like particles that could be recognized by antibodies against inserted epitopes. The ELISA assay showed that antibodies of COVID-19 patients can bind plant-produced HEV/RBD virus-like particles. This study shows that HEV capsid protein is a promising carrier for presentation of foreign antigen.

Automated summary

The capsid protein of Hepatitis E virus (HEV) can self-assemble into virus-like particles (VLPs) in plants and has the potential to be used as a carrier for antigens in vaccines. In this study, researchers inserted antigenic epitopes from Influenza A virus or SARS-CoV-2 spike glycoprotein into the truncated coat protein of HEV to optimize their presentation. The resulting fusion proteins, expressed in Nicotiana benthamiana plants, formed nanosized VLPs that were recognized by specific antibodies. This study demonstrates the promising potential of HEV capsid protein as a carrier for foreign antigens.