Chemical and genetic modification of virus-like particles for applications in vaccine design and drug delivery
Crooke, Stephen Nicholas
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Virus-like particles (VLPs) are multi-subunit protein assemblies that self-assemble into homogenous particles with periodic structure, making them ideal candidates for applications in biomedicine. This dissertation will discuss both the chemical and genetic modification of Qβ and PP7 VLPs for the design of vaccine platforms and drug delivery vehicles. Both the Qβ and PP7 VLPs are comprised of 180 copies of their respective coat protein (CP) monomers, which assemble to form icosahedral capsids of T = 3 geometry that are 28 and 30 nm in diameter, respectively. Herein, genetic engineering of the Qβ coat protein to introduce peptide and protein domains is described. First, these modifications were encoded as C-terminal extensions of the CP, and co-expression with unmodified subunits produced hybrid particles displaying the peptide or protein domains. These particles were successfully applied in both vaccination studies as well as the targeted delivery of prodrug-converting enzymes encapsulated within the VLP. To broaden the scope of targeting applications, the chemical conjugation of small molecules to the surface of Qβ VLPs was also used to direct cellular uptake and trafficking. The clearance of VLP delivery vehicles from circulation is an important factor governing their efficacy; to this effect, a survey of different polymer modifications and their effects on the immunological response to the Qβ VLP was undertaken. Lastly, PP7 VLPs were modified by genetically encoding extensions of a peptide implicated in mitigating phagocytic clearance to further explore strategies for prolonging circulation. All of the work presented here builds upon previous studies employing VLPs for drug delivery and vaccine development, while building upon the knowledge of chemical and genetic modifications that can be used to develop these materials. This work is poised to bring together the power of chemical and genetic modification in the development of nanoparticle platforms with novel properties that are equipped for effective vaccination and cellular targeting with reduced clearance in vivo.