Viral clearance studies are required for pharmaceuticals derived from human and/or animal sources such as recombinant proteins produced in eukaryotic cell lines, human blood products and vaccines, and even for some critical class III medical devices. It is mandatory to demonstrate that steps in the manufacturing process are capable of inactivating or removing potential viral contaminants. For this, a laboratory-scale (downscale) of the process step is developed and challenged with different model virus solutions. The viral concentrations are quantitatively determined in the feed material and the relevant product fraction. The ratio of both defines the reduction in virus and specifies the viral inactivation or viral removal capacity of the investigated process step…
Tag: <span>viral titer</span>
The licensing of recombinant vaccines produced using the baculovirus expression vector system (BEVS) has cleared the way for the production of a variety of biopharmaceuticals produced using this technology. Obtaining accurate estimates of both total and infectious baculovirus titer in upstream and downstream bioprocess fluids is one of many process controls that will need to be addressed during the development phase of a product’s lifecycle. Traditional plaque-titer methods require 5–7 days of incubation in order to reveal plaques that may be enumerated, and is further complicated by plaques created by multiple viruses that may be scored as a single plaque, thereby lowering the titer estimate. Titer assays based on polymerase chain reaction (PCR) have been developed, but they measure the presence of baculovirus genes, not virus particles. This often results in titers one or two logs higher than the actual titer. Immunoassays correlate with host cell infection and virus replication, but they too can be time-consuming and difficult to interpret. Our goal was to identify a method that would provide estimates of both total and infectious virus particles in as close to real-time as possible. We have evaluated the ViroCyt Virus Counter over the course of three years and have found it to provide accurate and reproducible estimates of both titer types in as little as 30 minutes. We have created an algorithm that converts total virus particle counts into estimates of infectious titer and tested these values in virus amplifications. The Virus Counter method of titer determination has also been used to track the quantity of virus particles in the culture supernatant of stirred-tank bioreactors infected with standard baculovirus stocks and with baculovirus-infected insect cells (BIIC)…
Recombinant protein expression using the Baculovirus Expression Vector System (BEVS) is a powerful tool for the production of therapeutics, diagnostics, and reagents. To maximize efficiency of protein production, and thereby reduce costs, it is important to optimize the production parameters. A crucial step in optimization is determining the best multiplicity of infection (MOI) for the system in use. Factors that can affect the MOI include the recombinant baculovirus itself as well as cell line type and media composition. Typically the titer of a viral stock is determined in a standard manner, and then that titer is applied to each and every parameter tested; for instance, titering the virus on a Spodoptera cell line in a serum-containing media, and then using those data to determine the MOI used to infect Trichoplusia cells in a serum-free media formulation. The results may suggest that either the Trichoplusia cell line or the media formulation is inadequate for protein expression when, in fact, the MOI was incorrect for that particular combination…
Variation of viral titre and recombinant product yields reported for the baculovirus expression vector system have been attributed to many specific infection variables. These include multiplicity of infection (MOI) and cell density at time of infection and time of harvest, as well as virus bank quality and efficiency. The MOI is defined as the number of plaque forming units (pfu) per cell that are added at the time of infection. Virus titre (pfu/ml) is determined by the plaque assay method. The MOI parameter is easily manipulated and may be important in optimising recombinant protein yields. Other sources of variation during both cell growth and viral infection phases may be responsible for the range of reported yields. Past studies in our laboratory compared the behaviour of cells infected with high and low MOI values, specifically regarding nutrient limitation and deprivation. In addition to these aspects, the quality of the virus bank may be an important factor which influences heterologous protein yields in the insect cell baculovirus system. Thus, production yields may be correlated to virus efficiency…