What are Virus-Like Particles?

Since interest is growing in the area of virus-like particles (VLPs), we would like to share some notes on what we’ve found in our research:

• VLPs are protein (e.g. envelope and/or capsid proteins) assemblies that highly resemble the native structure of their corresponding viruses but lack the viral genome, rendering them noninfectious.¹,²

• Their size is typically in the range of 22-150 nm.¹

• Applications of VLPs include prophylactic and therapeutic vaccines, gene delivery, and drug delivery.³

• Notable examples of successful commercialization of VLP vaccines are those against hepatitis B (based on the hepatitis B virus surface antigen) and human papilloma virus (HPV)-induced cervical cancer (based on the HPV capsid protein L1).²

• VLPs are typically produced from cells (e.g., baculocirus/insect cells, E. coli, and mammalian cells) using recombinant systems. The capsid proteins (one or more) and envelope protein (if present) assemble spontaneously upon expression.³

• Due to their relatively large size and complexity compared to monomeric proteins, purification of VLPs can be challenging. However, the processes already known to purify the native virus can be a starting point for developing a process for a corresponding VLP.² Impurities include contaminant proteins (e.g. host cell proteins), DNA (host or viral), incorrectly assembled particles, and endotoxin.³

• Some VLPs are stable enough to be concentrated and partially purified by precipitation with ammonium sulfate or polyethylene glycol.²

• For lab-scale purifications, ultracentrifugation in CsCl or sucrose gradients usually result in sufficient purity for research applications.2 Industrial-scale process involve multiple steps, usually including one or more chromatography (e.g., size exclusion, ion-exchange, affinity) steps.²,³

• In one example, chimeric Hepatitis B core antigen (HBcAg) VLPs expressed in E. coli were purified after cell lysis and clarification by precipitation by ammonium sulfate, cross-flow filtration (CFF), and finally multimodal size exclusion chromatography.⁴

• Due to their large, flow-through pores, membrane chromatography is a useful, scalable tool for VLP purification.³ For example, anion-exchange membrane chromatography was used to purify rotavirus VLPs.5 “Pseudo-affinity” sulfonated cellulose membranes have been used to purify influenza VLPs.⁶

• Purilogics would like to highlight a few of our products that are well-suited for purification of VLPs. Our Purexa™ NAEX Plus weak anion exchange and Purexa™ MQ multimodal strong anion exchange membranes contain tentacle type ligands resulting high capacity at high flow rates. Our Screen-NAEX and Screen-MQ programs allow customers to explore variables like tentacle length, tentacle density, pore size, and ligand hydrophobicity.

• Purilogics® Purexa™ SA is an affinity membrane chromatography product for selective purification of biologics that have binding affinity to sialic acid, such as many viral surface proteins. It contains a protein ligand that has a high density of sialic acid glycan residues, including those with α-2,6 and α-2,3 glycosidic linkages.
  
  

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References:

1. E.V.L. Grgacic, D.A. Anderson, Virus-like particles: Passport to Immune Recognition, Methods, 40 (2006) 60-65. https://dx.doi.org/10.1016%2Fj.ymeth.2006.07.018  
2. A. Zeltins, Construction and Characterization of Virus-Like Particles: A Review, Mol. Biotechnol., 53 (2013), 92-107. https://dx.doi.org/10.1007%2Fs12033-012-9598-4  
3. A. Roldao, A.C. Silva, M.C.M. Mellado, Viruses and Virus-Like Particles in Biotechnology: Fundamentals and Applications, Comprehensive Biotechnology, (2017), 633-656. https://dx.doi.org/10.1016%2FB978-0-12-809633-8.09046-4  
4. N. Hillebrandt, P. Vormittag, N. Bluthardt, A. Dietrich, J. Hubbuch, Integrated Process for Capture and Purification of Virus-Like Particles: Enhancing Process Performance by Cross-Flow Filtration, Front. Bioeng. Biotechnol., 8 (2020). https://doi.org/10.3389/fbioe.2020.00489  
5. T. Vicente, M.F.Q. Sousa, C. Peixoto, J.P.B. Mota, P.M. Alves, M.J.T. Corrondo, Anion-exchange Membrane Chromatography for Purification of Rotavirus-Like Particles, Journal of Membrane Science, 311 (2008), 270-283. https://doi.org/10.1016/j.memsci.2007.12.021  
6. S.B. Carvalho, A.R. Fortuna, M.W. Wolff, C. Peixoto, P.M. Alves, U. Reichl, M.J.T. Corrondo, Purification of Influenza Virus-Like Particles using Sulfonated Cellulose Membrane Adsorbers, J. Chem. Technol. Biotechnol., 93 (2018) 1988-1996. https://doi.org/10.1002/jctb.5474