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

Production of Baculovirus and Stem Cells for Baculovirus-Mediated Gene Transfer into Human Mesenchymal Stem Cells

The discovery of the genome-editing tool CRISPR-Cas9 is revolutionizing the world of gene therapy and will extend the gene therapy product pipeline. While applying gene therapy products, the main difficulty is an efficient and effective transfer of the nucleic acids carrying the relevant information to their target destination, the nucleus of the cells. Baculoviruses have shown to be very suitable transport vehicles for this task due to, inter alia, their ability to transduce mammalian/human cells without being pathogenic. This property allows the usage of baculovirus-transduced cells as cell therapy products, thus, combining the advantages of gene and cell therapy. To make such pharmaceuticals available for patients, a successful production and purification is necessary. In this chapter, we describe the generation of a pseudotyped baculovirus vector, followed by downstream processing using depth and tangential-flow filtration. This vector is used subsequently to transduce human mesenchymal stem cells. The production of the cells and the subsequent transduction process are illustrated.

Improving promiscuous mammalian cell entry by the baculovirus Autographa californica multiple nuclear polyhedrosis virus

The insect baculovirus AcMNPV (Autographa californica multiple nuclear polyhedrosis virus) enters many mammalian cell lines, prompting its application as a general eukaryotic gene delivery agent, but the basis of entry is poorly understood. For adherent mammalian cells, we show that entry is favoured by low pH and by increasing the available cell-surface area through a transient release from the substratum. Low pH also stimulated baculovirus entry into mammalian cells grown in suspension which, optimally, could reach 90% of the transduced population. The basic loop, residues 268-281, of the viral surface glycoprotein gp64 was required for entry and a tetra mutant with increasing basicity increased entry into a range of mammalian cells. The same mutant failed to plaque in Sf9 cells, instead showing individual cell entry and minimal cell-to-cell spread, consistent with an altered fusion phenotype. Viruses grown in different insect cells showed different mammalian cell entry efficiencies, suggesting that additional factors also govern entry.

Large-scale production and purification of VLP-based vaccines

Virus-like particles (VLPs) hold tremendous potential as vaccine candidates. These innovative biopharmaceuticals present the remarkable advantages of closely mimicking the three-dimensional nature of an actual virus while lacking the virus genome packaged inside its capsid. As a result, an equally efficient but safer prophylaxis is anticipated as compared to inactivated or live attenuated viral vaccines. With the advent of successful cases of approved VLP-based vaccines, pharmaceutical companies are indeed redirecting their resources to the development of such products. This paper reviews the current choices and trends of large-scale production and purification of VLP-based vaccines generated through the baculovirus expression vector system using insect cells.

Downstream processing of cell culture-derived virus particles

Manufacturing of cell culture-derived virus particles for vaccination and gene therapy is a rapidly growing field in the biopharmaceutical industry. The process involves a number of complex tasks and unit operations ranging from selection of host cells and virus strains for the cultivation in bioreactors to the purification and formulation of the final product. For the majority of cell culture-derived products, efforts focused on maximization of bioreactor yields, whereas design and optimization of downstream processes were often neglected. Owing to this biased focus, downstream procedures today often constitute a bottleneck in various manufacturing processes and account for the majority of the overall production costs. For efficient production methods, particularly in sight of constantly increasing economic pressure within human healthcare systems, highly productive downstream schemes have to be developed. Here, we discuss unit operations and downstream trains to purify virus particles for use as vaccines and vectors for gene therapy.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.

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.