Optimization of Colloid-Inspired Virus Vaccine Processing in Cell-Free Reactors
Virus-like particles (VLPs) have been developed as a vaccine against cervical cancer by Merck (West Point, PA, USA), and have recently been shown in animal studies to provide protection against both seasonal and avian influenza following intranasal administration (Novavax, Rockville, MD, USA). This new class of vaccines offers unprecedented immunoprotection, inherent safety, and a simple route of administration. However, current VLP manufacturing methods are unable to deliver products quickly and at minimal cost. This is in part due to the use of a cell-based processing route for VLP assembly followed by complex purification of the product from similarly sized nanoparticles or intraparticle contaminants. Manufacturing can potentially be simplified by chemical self-assembly of VLPs in a cell-free reactor. Current process optimization methods are empirical, with success gauged by low-resolution analytical techniques such as electron microscopy and ultracentrifugation, resulting in heterogeneous products of variable consistency. We have optimized the assembly of VLPs using fundamental colloidal science principles. By measuring the osmotic second virial coefficient (B22) of VLP precursors in various buffer conditions, we have gained insight into the interactions between the precursors that are responsible for VLP self-assembly. State-of-the-art characterization techniques such as field-flow fractionation have been used to quantitatively assess the quality of assembled VLPs. Understanding the precise nature of the interactions governing self-assembly, and how they are controlled by process parameters, has allowed us to establish a “self-assembly window” – a design and operation tool that gives robust control over this important process stage.