Osmolyte enhanced aqueous two-phase system for virus purification.

Due to the high variation in viral surface properties, a platform method for virus purification is still lacking. A potential alternative to the high-cost conventional methods is aqueous two-phase systems (ATPSs). However, optimizing virus purification in ATPS requires a large experimental design space, and the optimized systems are generally found to operate at high ATPS component concentrations. The high concentrations capitalize on hydrophobic and electrostatic interactions to obtain high viral particle yields. This study investigated using osmolytes as driving force enhancers to reduce the high concentration of ATPS components while maintaining high yields. The partitioning behavior of porcine parvovirus (PPV), a nonenveloped mammalian virus, and human immunodeficiency virus-like particle (HIV-VLP), a yeast-expressed enveloped VLP, were studied in a polyethylene glycol (PEG) 12 kDa-citrate system. The partitioning of the virus modalities was enhanced by osmoprotectants glycine and betaine, while trimethylamine N-oxide was ineffective for PPV. The increased partitioning to the PEG-rich phase pertained only to viruses, resulting in high virus purification. Recoveries were 100% for infectious PPV and 92% for the HIV-VLP, with high removal of the contaminant proteins and more than 60% DNA removal when glycine was added. The osmolyte-induced ATPS demonstrated a versatile method for virus purification, irrespective of the expression system.

Physiochemical properties of enveloped viruses and arginine dictate inactivation.

BACKGROUND: Therapeutic protein manufacturing would benefit by having an arsenal of ways to inactivate viruses. There have been many publications on the virus inactivation ability of arginine at pH 4.0, but the mechanism of this inactivation is unknown. This study explored how virus structure and solution conditions enhance virus inactivation by arginine and leads to a better understanding of the mechanism of virus inactivation by arginine. RESULTS: Large diameter viruses from the Herpesviridae family (SuHV-1, HSV-1) with loosely packed lipids were highly inactivated by arginine, whereas small diameter, enveloped viruses (equine arteritis virus (EAV) and bovine viral diarrhea virus (BVDV)) with tightly packed lipids were negligibly inactivated by arginine. To increase the inactivation of viruses resistant to arginine, arginine-derivatives and arginine peptides were tested. Derivates and peptides demonstrated that a greater capacity for clustering and added hydrophobicity enhanced virus inactivation. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) detected increases in virus size after arginine exposure, supporting the mechanism of lipid expansion. CONCLUSIONS: Arginine most likely interacts with the lipid membrane to cause inactivation. This is shown by larger viruses being more sensitive to inactivation and expansion of the viral size. The enhancement of arginine inactivation when increased hydrophobic molecules are present or arginine is clustered demonstrates a potential mechanism of how arginine interacts with the lipid membrane.

Mannitol-induced gold nanoparticle aggregation for the ligand-free detection of viral particles.

Traditional virus detection methods require ligands that bind to either viral capsid proteins or viral nucleic acids. Ligands are typically antibodies or oligonucleotides and they are expensive, have limited chemical stability, and can only detect one specific type of virus at a time. Here, the biochemical surface properties of viruses are exploited for ligand-free, nonspecific virus detection. It has been found that the osmolyte mannitol can preferentially aggregate virus, while leaving proteins in solution. This led to the development of a ligand-free detection of virus using gold nanoparticle (AuNP) aggregation. Porcine parvovirus (PPV) was incubated with AuNPs and aggregation of the PPV-AuNP complex with mannitol was detected by dynamic light scattering (DLS). The lowest detectable concentration of PPV was estimated to be 106 MTT50 per mL, which is lower than standard antibody assays. PPV was also detected when swabbed from a dry surface and in the presence of a protein solution matrix. The enveloped bovine viral diarrhea virus (BVDV) was also detected using mannitol-induced aggregation of BVDV-coated AuNPs. The lowest detectable concentration of BVDV was estimated to be 104 MTT50 per mL. This demonstrates that gold nanoparticle aggregation can detect virus without the use of specific ligands.

Tie line framework to optimize non-enveloped virus recovery in aqueous two-phase systems.

Viral particle purification is a challenge due to the complexity of the broth, the particle size, and the need to maintain virus activity. Aqueous two-phase systems (ATPSs) are a viable alternative for the currently used and expensive downstream processes. This work investigated the purification of two non-enveloped viruses, porcine parvovirus (PPV), and human rhinovirus (HRV) at various ATPS tie lines. A polyethylene glycol (PEG) 12 kDa-citrate system at pH 7 was used to study the behavior of the partitioning on three different thermodynamic tie line lengths (TLLs). It was experimentally determined that increasing the TLL, and therefore increasing the hydrophobic and electrostatic driving forces within the ATPS, facilitated higher virus recoveries in the PEG-rich phase. A maximum of 79% recovery of infectious PPV was found at TLL 36 w/w% and tie line (TL) ratio 0.1. Increased loading of PPV was studied to observe the change in the partitioning behavior and similar trends were observed for all the TLs. Most contaminants remained in the citrate-rich phase at all the chosen TLLs, demonstrating purification of the virus from protein contaminants. Moderate DNA removal was also measured. Net neutral charged HRV was studied to demonstrate the effects of driving forces on neutrally charged viruses. HRV recovery trends remained similar to PPV on each TLL studied, but the values were lower than PPV. Recovery of viral particles in the PEG-rich phase of the PEG-citrate system utilized the difference in the surface hydrophobicity between virus and proteins and showed a direct dependence on the surface charge of each studied virus. The preferential partitioning of the relatively hydrophobic viral particles in the PEG-rich phase supports the hypothesis that both hydrophobic and electrostatic forces govern the purification of viruses in ATPS.