![]() However, more advanced chromatographic steps and scalable technologies are being implemented. Indeed, not only does each virus have its own properties and behavior, but the treatment that viruses can undergo also depends on the nature of the final product: Should the virus be inactivated or live-attenuated retaining infectivity properties, does the particle structure have to be maintained for immunogenicity, or should the virus, that might be defective, retain the properties to effectively transduce cells and express the targeted transgene, as is the case for viral vectors used in gene therapy or vaccination? Traditional techniques for purifying EVs and viruses involved ultracentrifugation and filtration and are still being used extensively. No unique stream exists in the downstream processing of viral vectors and vaccines. Although techniques have greatly improved over the years to generate purer high-quality products and reproducible processes while maintaining or decreasing the cost of goods, regulatory agencies are increasingly stringent regarding product identity and characterization of the end products and level of acceptable impurities as a way to ensure public safety and maintain public trust in this class of medicine. ![]() ![]() Purification process unit operations usually start with harvest and clarification, followed by intermediate purification steps, before polishing and formulation steps. The manufacturing of viral vector and viral vaccine products has always been paved with challenges related to the downstream processing. These enveloped viruses are produced in various systems, including traditional embryonated chicken eggs or more advanced cell culture technologies such as MRC-5 cells, Vero cells and HEK293-derived cell lines. Enveloped viruses are encased in a lipid bilayer which, in most cases, fuses with the target host cell membrane to infect cells. ![]() About 14% of vaccines approved by the FDA involve enveloped viruses, while out of the 15 gene therapy products approved worldwide in 2019, six of them use enveloped viruses, and 39% of gene therapy clinical trials are using enveloped viruses. Viral vectors and viral vaccines are invaluable tools in prevention and treatment of diseases. ![]()
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