Engineering Protein Cage Nanoparticles as Plug-and-treatable Nanovaccine Platforms

Abstract

Protein cage nanoparticles are protein-based supramolecular virus-like particles and attractive candidates for nano-scale cargo delivery vehicles. While the interior surfaces of the protein cages have been used for encapsulation, attachment and synthesis of organic and inorganic materials, their exterior surfaces have been used for multivalent presentations of molecules, including affinity tags, antibodies, fluorophores, carbohydrates, nucleic acids, and peptides, for molecular targeting, hierarchical structure formation, and antigen display. Using these natural properties, protein cage nanoparticles have been used as virus-mimicking antigen-delivery nanoplatforms and targeted delivery nanoplatforms of therapeutics and/or diagnostics. Antigen-bearing protein cage nanoparticles successfully induced dendritic cell (DC)-mediated antigen-specific T-cell immune responses and consequent melanoma tumor rejection in vivo. We also implemented protein cage nanoparticles as resonance T1 contrast conjugate nanoplatforms via site-selective attachment of Gd(III)-chelating agents and used them for in vivo MR imagings. By applying a recently developed bacterial superglue, SpyTag/SpyCatcher protein ligation system, to targeting affibody/nanobody molecules and protein cage nanoparticles, multiple displays of two or more targeting ligands or one type of targeting ligand with therapeutic effector biomolecules on a polyvalent single nanoparticle were achieved and their superior capability of target-cancer cell monitoring and tumor growth suppression was confirmed. In addition to targeted drug and/or probe delivery, protein cage nanoparticles can be used as nanoplatforms for developing plug-and-treatable nanovaccines with a SpyTag/SpyCatcher protein ligation system. A variety of protein cage nanoparticles having multiple geometries were engineered to display SpyTag or SpyCatcher on their exterior surface and attachable SpyTag- or SpyCatcher-fused subunit antigens were independently generated. A SpyTag/SpyCatcher protein ligation system allowed us to display multiple copies of single type antigen or multi-antigens on a protein cage nanoparticle in a mix-and-match manner leading to develop efficient plug-and-treatable nanovaccines.