Production of virus-like particles of nervous necrosis virus displaying partial VHSV's glycoprotein at surface and encapsulating DNA vaccine plasmids

In order to use nervous necrosis virus (NNV) virus-like particles (VLPs) as a delivery tool for heterologous antigens or plasmids, we attempted to produce red-spotted grouper nervous necrosis virus (RGNNV) VLPs displaying a partial region of viral hemorrhagic septicemia virus (VHSV) glycoprotein at the surface and VLPs that are harboring DNA vaccine plasmids within the VLP. A peptide encoding 105 amino acids of VHSV glycoprotein was genetically inserted in the loop region of NNV capsid gene, and VLPs expressing the partial part of VHSV glycoprotein were successfully produced. However, in the transmission electron microscope analysis, the shape and size of the partial VHSV glycoprotein-expressing NNV VLPs were irregular and variable, respectively, indicating that the normal assembly of capsid proteins was inhibited by the relatively long foreign peptide (105 aa) on the loop region. To encapsulate by simultaneous transformation with both NNV capsid gene expressing plasmids and DNA vaccine plasmids (having an eGFP expressing cassette under the CMV promoter), NNV VLPs containing plasmids were produced. The encapsulation of plasmids in the NNV VLPs was demonstrated by PCR and cells exposed to the VLPs encapsulating DNA vaccine plasmids showed fluorescence. These results suggest that the encapsulation of plasmids in NNV VLPs can be done with a simple one-step process, excluding the process of disassembly-reassembly of VLPs, and NNV VLPs can be used as a delivery tool for DNA vaccine vectors.