HEV is a non-enveloped, feco-orally transmitted RNA virus. The viral capsid protein, when expressed in insect cells, can self-assemble such that 60 monomeric units form an icosahedral (twenty faceted) protein shell known as a virus like particle (VLP). Like HEV virions, VLPs are resistant to harsh environmental conditions, such as acidic and intestinal pH, and extremes of temperature. This makes HEV VLP highly suitable for use as an orally-deliverable nano-carriers and vaccine/therapeutic agent.
The HEV VLP is uniquely modular, and extensive modification of the surface spikes by genetic engineering or chemical modification does not affect the formation of a stable, icosahedral scaffold. Additionally, the modifications are displayed in their correct conformations on the VLP surface. We have made recombinant HEV VLPs displaying antigenic epitopes from HIV envelope proteins, or chemically modified to express breast cancer targeting ligands on the surface. These VLPs are structurally similar to wild type VLPs, but chemically resemble the derivatizations on their surfaces. For example, oral administration of HIV epitope-chimeric VLPs induced a strong and specific immune response in mice. The breast cancer targeting VLPs successfully trafficked to tumor sites in vivo and in cells.
Modularity also enables the VLP to be disassembled and reassembled in vitro in the appropriate chemical environment. Critical positive charges on the inner surface of the VLP stabilize its re-assembly, and negatively charged molecules such as DNA can be encapsulated of DNA in the re-assembled particle. We encapsulated DNA encoding HIV proteins in the VLPs, and administered them orally in mice. Gag protein was expressed in gut epithelial sections, and a highly specific anti-Gag immune response was generated as well. By fine-tuning various parameters of vaccine development, such as optimizing the efficiency of DNA encapsulation and modifying the VLP surface for better targeting to specific cell types, we wish to develop a simple but effective targeting tool that has enormous clinical implications. Additional modification of the particle can enable labeling for various imaging modalities, such as electron microscopy and in situ fluorescence imaging.