Andreas Immelmann, Ph.D., managing director of Analysis (www.analysis-gmbh.de), a firm providing validation of viral clearance in the downstream processing of biologicals, presented information on some of the problems being faced when designing viral clearance studies.
"Validation studies can take up to four months, so manufacturers need to plan studies well ahead. Studies should be planned and conducted not only by production bioengineers but also by virologists, as you cannot expect them to be familiar with the manufacturing process. Therefore, virologists need to be included or there will be problems when studies are taken from the laboratory to process scale.
"One of the greatest technical challenges we are facing in bioprocessing is removing the non-envelope viruses, such as the model porcine parvovirus. Ethanol has been the classical method of virus removal, but lately nanofiltration is being considered as a viable alternative.
This is because filters that have 20-nm pore sizes are becoming more widely available and membrane filtration can be easily integrated into the purification process," said Dr. Immelmann.
To prove that ion adsorption filtration offers a good technique for removing non-envelope viruses, Ranil Wickramasinghe, Ph.D., associate professor at Colorado State University, presented the results of his research.
Dr. Wickramasinghe's team challenged four Sartorius anion and cation exchange membranes with the parvovirus Aedes aegypti desonucleosis virus (AeDNV) and tested for the presence of viruses within the filtrate by PCR.
"Viruses are generally negatively charged, and since the pores within an anionic membrane filter are positively charged, theoretically this means that this type of membrane should remove viruses. With column chromatography, you have complicating effects due to size exclusion.
"Further, diffusion through the media particles is slow and makes removing viruses and viral vectors difficult, whereas this is not the case with membrane filters," explained Dr. Wickramasinghe.
The results of the research show anion exchange membranes remove AeDNV, whereas the cation exchange membranes do not. Therefore, these types of membranes have potential uses for viral clearance in biopharmaceutical manufacture or for purifying viral vectors in gene therapy and viral vaccine production, both of which are difficult to do with column chromatography."