Proceedings of the 2019 Viral Clearance Symposium, Session 3: Continuous Processing.

Successful implementation of continuous processing requires an understanding of how to incorporate viral testing and clearance/inactivation into the process via representative small-scale models. Following the lead of the 2017 Viral Clearance Symposium, a session was devoted to understanding the impact of continuous process conditions on viral safety, how to design process for continuous viral inactivation/removal, and how to leverage existing batch data for a continuous process. In this session, there was a presentation investigating the impact of extended continuous cell culture on the production of endogenous retroviral-like particles, two presentations on the robustness of multicolumn capture chromatography and continuous viral filtration for clearance of viral particles, two talks on leveraging well-characterized batch processing data and scientific knowledge to demonstrate viral clearance capabilities of continuous processing, and finally two presentations related to process designs for continuous viral inactivation. Overall, this session provided additional scientific knowledge to support viral clearance strategies when implementing a continuous manufacturing process.

Proceedings of the 2019 Viral Clearance Symposium, Session 2: New Modalities in Chromatography and Adsorptive Filters.

In Session 2 of the 2019 Viral Clearance Symposium, new outcomes of viral clearance performance of polishing chromatography and depth filters utilized in the purification processes of biotechnologically produced recombinant proteins such as monoclonal antibodies were presented. It was shown that flow through both multimodal anion-exchange and anion-exchange chromatography are effective tools for removal of retroviruses and, under defined conditions, also for parvoviruses. Cation-exchange chromatography, when operated in bind/elute mode, hydrophobic interaction chromatography, and depth filtration can also be potent for virus removal, but are less robust for parvoviruses. Despite these data provide further understanding of virus removal mechanisms by chromatography and depth filtration operations, more investigation is required for a clear understanding of the molecular mechanisms of virus removal and the relevance of different moleculés interactions including resin, virus, and product.

Genome Sequences of Bacteriophages KaiHaiDragon and OneinaGillian, Isolated from Microbacterium foliorum in Riverside, California.

KaiHaiDragon and OneinaGillian are two bacteriophages which have been recovered from soil samples using the bacterial host Microbacterium foliorum Their genome lengths are 52,992 bp and 61,703 bp, with 91 and 104 predicted open reading frames, respectively. KaiHaiDragon belongs to cluster EC, and OneinaGillian is a member of cluster EG.

Proceedings of the 2017 Viral Clearance Symposium, Session 4: Submission Strategies.

Appropriate performance of virus validation studies and testing of unprocessed bulk harvests for retrovirus particle count are procedures in the demonstration of an acceptable level of viral safety for cell-derived biotechnology products. Product-specific validation studies on virus reduction with two model viruses [usually murine leukemia virus (MuLV) and a parvovirus] performed in duplicate runs are standard for clinical trial applications. For the retroviral safety margin, a 6 log reduction is normally expected. Retroviral particle counts are measured traditionally by transmission electron microscopy (TEM) and are commonly performed at contract laboratories. These procedures are quite time-consuming and can be associated with significant costs. In particular, the time factor is a hurdle for companies that want to quickly bring their new products to the clinic. In this session, several strategies on how to lower time, cost, and workload in the evaluation of viral safety for early clinical trial applications, while still ensuring sufficient level of viral safety of the product, were presented. In addition, virus reduction strategies for molecules that do not have the standard antibody structure are presented. Also presented in this session is the feasibility of the use of retrovirus-like particle (RVLP) in the prevalidation of virus removal and the use of quantitative polymerase chain reaction (qPCR) as an alternative to infectivity assays in virus validation studies as well as its use as an alternative to quantitative TEM analysis for determining RVLP count in the bulk harvest of a perfusion bioreactor.LAY ABSTRACT: In this session, several strategies on how to lower time, cost, and workload in the evaluation of viral safety for early clinical trial applications of cell-derived biotechnology products, while still ensuring sufficient level of viral safety of the product, were presented. In addition, virus reduction strategies for molecules that do not have the standard antibody structure are presented. Also presented in this session is the feasibility of the use of retrovirus-like particle (RVLP) in the prevalidation of virus removal and the use of quantitative polymerase chain reaction (qPCR) as an alternative to infectivity assays in virus validation studies as well as its use as an alternative to quantitative TEM analysis for determining RVLP count in the bulk harvest of a perfusion bioreactor.

A consensus rating method for small virus-retentive filters. I. Method development.

Virus filters are membrane-based devices that remove large viruses (e.g., retroviruses) and/or small viruses (e.g., parvoviruses) from products by a size exclusion mechanism. In 2002, the Parenteral Drug Association (PDA) organized the PDA Virus Filter Task Force to develop a common nomenclature and a standardized test method for classifying and identifying viral-retentive filters. One goal of the task force was to develop a test method for small virus-retentive filters. Because small virus-retentive filters present unique technical challenges, the test method development process was guided by laboratory studies to determine critical variables such as choice of bacteriophage challenge, choice of model protein, filtration operating parameters, target log10 reduction value, and filtration endpoint definition. Based on filtration, DLS, electrospray differential mobility analysis, and polymerase chain reaction studies, a final rating based on retention of bacteriophage PP7 was chosen by the PDA Virus Filter Task Force. The detailed final consensus filter method was published in the 2008 update of PDA Technical Report 41. Virus Filtration.

A consensus rating method for small virus-retentive filters. II. Method evaluation.

Virus filters are membrane-based devices that remove large viruses (e.g., retroviruses) and/or small viruses (e.g., parvoviruses) from products by a size exclusion mechanism. In 2002, the Parenteral Drug Association (PDA) organized the PDA Virus Filter Task Force to develop a common nomenclature and a standardized test method for classifying and identifying viral-retentive filters. A test method based on bacteriophage PP7 retention was chosen based on developmental studies. The detailed final consensus filter method is published in the 2008 update of PDA Technical Report 41: Virus Filtration. Here, we evaluate the method and find it to be acceptable for testing scaled-down models of small virus-retentive filters from four manufacturers. Three consecutive lots of five filter types were tested (Pegasus SV4, Viresolve NFP, Planova 20N and 15N, Virosart CPV). Each passed the criteria specified in the test method (i.e., >4 log10 PP7 retention, >90% intravenous immunoglobulin passage, and passing integrity/installation testing) and was classified as PP7-LRV4.

Purification of densonucleosis virus by tangential flow ultrafiltration.

Purification at commercial scale of viruses and virus vectors for gene therapy applications and viral vaccines is a major separations challenge. Tangential flow ultrafiltration has been developed for protein purification. Here tangential flow ultrafiltration of parvoviruses has been investigated. Because these virus particles are small (18-26 nm), removal of host cell proteins will be challenging. The results obtained here indicate that 30, 50, and 100 kDa membranes reject the virus particles, whereas 300 kDa membranes allow some virus particles to pass into the permeate. The decrease in permeate flux for the 300 kDa ultrafiltration membrane is much greater than for the 30, 50, and 100 kDa membranes, indicating possible entrapment of virus particle in the membrane pores. The permeate flux and level of protein rejection is strongly affected by the cell culture growth medium. The results indicate that when developing a new process, it is essential that the cell culture and purification operations be developed in parallel.

Binding Aedes aegypti densonucleosis virus to ion exchange membranes.

Experimental and numerical results for binding Aedes aegypti densonucleosis virus (AeDNV) using anion and cation exchange membranes are presented. AeDNV particles are adsorbed by anion and cation exchange membranes providing the virus particles and membranes are oppositely charged. Q membranes which are strongly basic anion exchangers were the most effective. Dynamic and static capacities for Q membranes were found to be similar. A numerical model is proposed which assumes a log normal pore size distribution. By estimating the required parameters from static binding experiments, the model may be used to calculate the breakthrough curve for virus adsorption.

Densonucleosis virus purification by ion exchange membranes.

Preparative chromatography is widely used in the downstream purification of biopharmaceutical products. Replacement of resins by membranes as chromatographic supports, overcomes many of the limitations associated with resin-based chromatography such as high-pressure drops, slow processing rates due to pore diffusion and channeling of the feed through the bed. In particular, adsorptive membranes may be ideally suited for virus capture. Virus capture is critical in a number of applications. In gene therapy and vaccine production, large-scale purification of virus vectors is often essential. In the manufacture of biopharmaceuticals, validation of virus clearance is critical. Here results for purification of Aedes aegypti densonucleosis virus (AeDNV) using anion and cation exchange membranes are presented. AeDNV is a non-enveloped, single-stranded mosquito-specific parvovirus. Virus particles are around 20 nm in size. AeDNV could find potential applications in integrated vector-borne disease control programs. In addition, capture of parvovirus for validation of virus clearance in the manufacture of biopharmaceuticals is of commercial importance. By adjusting the pH of the feed stream, AeDNV particles may be adsorbed by both anion and cation exchange membranes. However, strongly basic anion exchange membranes were the most effective in adsorbing AeDNV particles. Adsorption and subsequent elution of AeDNV by anion exchange membranes leads to significant virus concentration. Dynamic and static capacities for anion exchange membranes were similar. Further, a sharp elution curve was obtained suggesting that pore diffusional resistances are insignificant. The adsorption of AeDNV particles by anion exchange membranes may be described by a linear isotherm.