Criteria For Choosing a Virus-Like Display Platform Immunogenicity Potential Antigen Display Potential Production Potential Intellectual Property Issues
Immunogenicity Potential Particulate - uptake by APCs for CMI High density display: 50-100Å repeats - BCR activation Rigid Conformation vs Freely Diffusible in Membrane? Naked Icosohedral VLPs vs HBs Ag particles/liposomes Encapsidatation of Nucleic Acid as TLR agonist? Usefulness of Exogenous Adjuvant? Are preexisting Abs to the vector an issue?
Naked Icosahedral Virions Vary in Size, But the Distance Between Subunits Stays the Same Baker et al. Microbiol Mol Biol Rev 1999; 63:862
Immunogenicity Potential Particulate - uptake by APCs for CMI High density display: 50-100Å repeats - BCR activation Rigid Conformation vs Freely Diffusible in Membrane? Naked Icosohedral VLPs vs HBs Ag particles/liposomes Encapsidatation of Nucleic Acid as TLR agonist? Usefulness of Exogenous Adjuvant? Are preexisting Abs to the vector an issue?
HBsAg Particles Are S Proteins Floating in a Yeast Lipid Membrane MaAleeer et al. Nature 1984; 307: 178-80
Immunogenicity Potential Particulate - uptake by APCs for CMI High density display: 50-100Å repeats - BCR activation Rigid Conformation vs Freely Diffusible in Membrane? Naked Icosohedral VLPs vs HBs Ag particles/liposomes Encapsidatation of Nucleic Acid as TLR agonist? Usefulness of Exogenous Adjuvant? Are preexisting Abs to the vector an issue?
Approaches For Virus-Like Display Genetic Fusion Virion Capsid Protein Target sequence Overexpression HBcAg Parvovirus Chemical Conjugation Target Peptide Cys + Sulfo-MBS (cross-linker) Qbeta Conjugate to Pre-formed Capsids Activated Biotin + Streptavidin Bridging Biotin Binding Site Conjugated SA-Target HPV VLPs Wild-type SA Tetramer Biotinylated Target Ag
Antigen Display Potential Conjugation to Preformed VLPs: Flexible with regard to antigen More complex manufacturing Genetic fusion w/ major capsid protein Limited to short peptides Inserts are often incompatible with assembly Less complex manufacturing
A Partial List of VLPs Used as Vaccine Platforms VLP Type Linking Method Target Antigen Animal Viruses Hepadnavirus Core Genetic, Chemical malaria, flu, FMDV, HCV (HBV, WHV, DHV) hantavirus, others HPV Genetic, Chemical HIV, flu, HPV E2 and E7, P1A tumor Ag Parvovirus Genetic dengue virus, anthrax (PPV, B19) LCMV Mouse Polymavirus Genetic Her2/Neu Plant Viruses CPMV Genetic, Chemical HIV, rinovirus, MEV, Pseuomonas TMV Genetic, Chemical HPV L2, melanoma Ags Bacteriophage Qβ Chemical nicotine, Der p1 allergen LCMV MS2 Genetic HIV Yeast Ty particles Genetic HIV, flu B Chackerian Expert Rev Vaccines 2007; 6:381-90
Lamba gpd Trimers Are Displayed At High Denisity on the Phage Head Yang et al., Nat Struct Biol 7: 230-7, 2000 Lambda gpd inserts into the surface of preformed phage heads It is remarkably tolerant of genetic insertions at both the C- and N-terminus
AAV Display: Panning a Random Peptide Library for a Mimitope Plasmid - Pool 587 587 NotI AscI 588 Selection with MoAb to Target Ag Transfection 293 cells Y Y Y Y Packaging AAV library Y Y Y Y Thaw/Freeze Wash off 10 7 clones Target cells Perabo et al., Mol. Ther. 2003
Nanoparticles: : Synthetic VLPS SARS T = 1 23 nm T = 3 28 nm T. Pimentel et al. Chem Biol Drug Des 2009; 73:53-61
Production Potential Efficient and low cost vaccine manufacture and delivery is critical for wide spread distribution in low resource settings. Comparative studies of vaccine yields and stability are rarely conducted. Difficult to project industrial scale GMP yields based upon results in academic laboratories. Industry rarely reveals cost of vaccine production.
Intellectual Property Issues IP is needed to attract corporate investment. IP can trump science when companies make decisions. Many of the VLP platforms were never patented or are off patent. Specific vaccine candidates are/will be patented. Most current patents were not prosecuted in developing countries. Emerging country manufacturers may have the freedom to operate in in developing countries despite patents issued in developed countries.
Conclusions Inherent immunogenicity of VLP platforms may be similar, at least if naked icosohedral. Ability to generate a conformationally correct antigen in a cost effective manner may be a more discriminating factors. Corporate decisions on platforms will be driven primarily by IP issues and production experience.