Potato Virus M-Like Nanoparticles: Construction and Characterization.

Virus-like particles (VLPs) are multisubunit self-assembly competent protein structures with identical or highly related overall structure to their corresponding native viruses. To construct a new filamentous VLP carrier, the coat protein (CP) gene from potato virus M (PVM) was amplified from infected potato plants, cloned, and expressed in Escherichia coli cells. As demonstrated by electron microscopy analysis, the PVM CP self-assembles into filamentous PVM-like particles, which are mostly 100-300 nm in length. Adding short Gly-Ser peptide at the C-terminus of the PVM, CP formed short VLPs, whereas peptide and protein A Z-domain fusions at the CP N-terminus retained its ability to form typical PVM VLPs. The PVM-derived VLP carrier accommodates up to 78 amino acid-long foreign sequences on its surface and can be produced in technologically significant amounts. PVM-like particles are stable at physiological conditions and also, apparently do not become disassembled in high salt and high pH solutions as well as in the presence of EDTA or reducing agents. Despite partial proteolytic processing of doubled Z-domain fused to PVM VLPs, the rabbit IgGs specifically bind to the particles, which demonstrates the functional activity and surface location of the Z-domain in the PVM VLP structure. Therefore, PVM VLPs may be recognized as powerful structural blocks for new human-made nanomaterials.

Silica nanoparticles as the adjuvant for the immunisation of mice using hepatitis B core virus-like particles.

Advances in nanotechnology and nanomaterials have facilitated the development of silicon dioxide, or Silica, particles as a promising immunological adjuvant for the generation of novel prophylactic and therapeutic vaccines. In the present study, we have compared the adjuvanting potential of commercially available Silica nanoparticles (initial particles size of 10-20 nm) with that of aluminium hydroxide, or Alum, as well as that of complete and incomplete Freund's adjuvants for the immunisation of BALB/c mice with virus-like particles (VLPs) formed by recombinant full-length Hepatitis B virus core (HBc) protein. The induction of B-cell and T-cell responses was studied after immunisation. Silica nanoparticles were able to adsorb maximally 40% of the added HBc, whereas the adsorption capacity of Alum exceeded 90% at the same VLPs/adjuvant ratio. Both Silica and Alum formed large complexes with HBc VLPs that sedimented rapidly after formulation, as detected by dynamic light scattering, spectrophotometry, and electron microscopy. Both Silica and Alum augmented the humoral response against HBc VLPs to the high anti-HBc level in the case of intraperitoneal immunisation, whereas in subcutaneous immunisation, the Silica-adjuvanted anti-HBc level even exceeded the level adjuvanted by Alum. The adjuvanting of HBc VLPs by Silica resulted in the same typical IgG2a/IgG1 ratios as in the case of the adjuvanting by Alum. The combination of Silica with monophosphoryl lipid A (MPL) led to the same enhancement of the HBc-specific T-cell induction as in the case of the Alum and MPL combination. These findings demonstrate that Silica is not a weaker putative adjuvant than Alum for induction of B-cell and T-cell responses against recombinant HBc VLPs. This finding may have an essential impact on the development of the set of Silica-adjuvanted vaccines based on a long list of HBc-derived virus-like particles as the biological component.