Anion-exchange membrane chromatography for purification of rotavirus-like particles

Geminiviral vectors based on bean yellow dwarf virus for production of vaccine antigens and monoclonal antibodies in plants

Expression of recombinant vaccine antigens and monoclonal antibodies using plant viral vectors has developed extensively during the past several years. The approach benefits from high yields of recombinant protein obtained within days after transient delivery of viral vectors to leaves of Nicotiana benthamiana, a tobacco relative. Modified viral genomes of both RNA and DNA viruses have been created. Geminiviruses such as bean yellow dwarf virus (BeYDV) have a small, single stranded DNA genome that replicates in the nucleus of an infected plant cell, using the cellular DNA synthesis apparatus and a virus-encoded replication initiator protein (Rep). BeYDV-derived expression vectors contain deletions of the viral genes encoding coat and movement proteins and insertion of an expression cassette for a protein of interest. Delivery of the geminiviral vector to leaf cells via Agrobacterium-mediated delivery produces very high levels of recombinant DNA that can act as a transcription template, yielding high levels of mRNA for the protein of interest. Several vaccine antigens, including Norwalk virus capsid protein and hepatitis B core antigen, were expressed using the BeYDV vector at levels up to 1 mg per g of leaf mass. BeYDV replicons can be stacked in the same vector molecule by linking them in tandem, which enables production of multi-subunit proteins like monoclonal antibody (mAb) heavy and light chains. The protective mAb 6D8 against Ebola virus was produced at 0.5 mg per g of leaf mass. Multi-replicon vectors could be conveniently used to produce protein complexes, e.g. virus-like particles that require two or more subunits.

Impact of ligand density on the optimization of ion-exchange membrane chromatography for viral vector purification

The effect of ligand density on anion-exchange membrane chromatography (AEXmc) for the purification of recombinant baculoviruses (rBVs), potential viral vectors in clinical applications, is studied by surface plasmon resonance on customized AEX surfaces and gradient elution experiments on Sartobind D membrane prototypes with different diethylamine ligand densities, complemented by dynamic light scattering analysis for estimation of the hydrodynamic particle size of the various biologics. A chromatographic-column model based on the steric mass action model of ion exchange is employed to analyze the gradient-elution AEXmc experiments, extrapolate the results to other operating conditions, and provide directions for process improvement. Although counterintuitively, the experimental evidence provided in this study shows that the lowering of ligand density is beneficial for rBV purification by AEXmc in bind-and-elute-mode, because it decreases the residual concentrations of host cell protein, dsDNA, and non-infective rBVs in the eluted product cut, and increases the overall yield by roughly 20% over current standard values. Overall, we present a case study on how rational design can streamline downstream process development.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

Viruses and Virus-Like Particles in Biotechnology

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this article, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitorization, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Norwalk virus-like particles as vaccines

Noroviruses (NoV) cause the great majority of epidemic nonbacterial gastroenteritis in humans. Expression of the capsid protein in recombinant systems, including insect and plant cells, yields assembly of virus-like particles (VLPs) that mimic the antigenic structure of authentic virions, and are relatively acid- and heat-stable. Norwalk virus (NV), the prototype NoV, has been studied extensively, and Norwalk virus-like particles (NVLPs) produced in insect cells and plants are immunogenic in mice and humans when delivered orally, stimulating the production of systemic and mucosal anti-NV antibodies. NVLPs are also highly immunogenic when delivered intranasally, provoking antibodies at levels similar to orally delivered VLP at much lower doses. Oral and nasal delivery of NVLPs efficiently produces antibodies at distal mucosal sites, which suggests that NVLPs could be used to deliver heterologous peptide antigens by production of genetic fusion chimeric capsid proteins. Examination of norovirus VLP surface structures and receptor binding motifs facilitates identification of potential sites for insertion of foreign peptides that will minimally affect the efficiency of VLP assembly and receptor binding. Thus, there is strong potential to use norovirus VLPs as vaccine-delivery vehicles.

Modeling electrostatic interactions of baculovirus vectors for ion-exchange process development

Product-related impurities constitute a major burden in the production of recombinant viral vectors for gene therapy and vaccination; it impairs not only the biological efficacy of the preparation but the process yield/productivity. Recombinant baculovirus was used as an enveloped virus model to address this issue. Given that ion-exchange chromatography is a process of choice for purification of viral vectors, the analysis of the electrostatic behavior can be instrumental for the improvement of impurity removal. The main species, product (infective virus particle) and product-derived impurities (dsDNA-, glycoprotein-, and envelope-deprived baculovirus particles), were isolated and correspondent zeta potentials were analyzed through dynamic light scattering. A model of the virus based on the viral components critical for biological function is proposed. The contribution of these viral components to the overall particle electrostatic interaction energy profile (calculated between the particle and a putative ion-exchange surface) was assessed as a function of ionic strength and pH. This resulted in a deterministic tool capable of distinguishing the electrostatic properties of the infective virus particle from the major virus-related impurities. Within an ion-exchange bind-elute process, this knowledge helps narrow the optimization space in early stage process development for viral vectors by predicting the best selectivity conditions.

Modeling protein binding and elution over a chromatographic surface probed by surface plasmon resonance

Surface plasmon resonance (SPR) spectroscopy is used as a scaled-down, analytical, pseudo-chromatography tool for analyzing protein binding and elution over an ion-exchange surface under cyclic sorption conditions. A micrometric-scale adsorption surface was produced by immobilizing a typical ion exchange ligand--diethylaminoethyl (DEAE)--onto commercially available planar gold sensor chip surfaces pre-derivatized with a self-assembled monolayer of 11-mercaptoundecanoic acid with known density. An explicit mathematical formulation is provided for the deconvolution and interpretation of the SPR sensorgrams. An adsorption rate model is proposed to describe the SPR sensorgrams for bovine serum albumin, used here as model protein, when the DEAE surface is subjected to a cyclic series of binding and elution steps. Overall, we demonstrate that the adsorption rate model is capable of quantitatively describing BSA binding and elution for protein titers from dilute conditions up to overloaded conditions and a broad range of salt concentrations.