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Figure 1. Generic flowchart of current downstream processes for gene therapy vectors and inactivated virus vaccines.
(Figure omitted. See article PDF.)
Virus particles are currently used for medical [1-5], analytical and scientific applications [6-9], and as bioinsecticides [10,11]. Recently, medical applications are gaining an increasing interest owing to the growing markets for viral vaccines (Table 1) and the potential broad usage of viral gene therapy vectors. Vaccines, administered to prevent or treat viral diseases, are mainly based on attenuated or killed viruses, membrane fractions derived from purified virus particles, or recombinant viral proteins expressed in various hosts. Examples of successful attenuated or killed virus vaccines are influenza, measles, mumps, rubella, rotavirus, yellow fever and varicella [3,4,12,13]. Gene therapy involves the transfer of genetic information to cells or tissues of individuals to achieve a therapeutic effect [14]. Therefore, required genes are largely delivered by viral vector systems based, for example, on the herpes simplex virus, adenovirus, adeno-associated virus (AAV), retrovirus (e.g., lentivirus) and Vaccinia virus [1,15]. Currently, numerous clinical gene therapy trials are conducted to investigate the treatment of diseases such as cancer, cystic fibrosis, Alzheimer's, Parkinson's, hemophilia and HIV/AIDS [5,16,17].
The broad spectrum of these applications and the current expansions of medical markets underline the ongoing efforts to improve production procedures for viral vaccines and gene therapy vectors. One striking example is the development of cell culture-derived influenza vaccines. While conventional production processes rely on egg-based systems, optimized cell culture systems are currently being established to cope with sudden demands for pandemic vaccines and increasing supply of seasonal vaccines. With advances in upstream procedures to increase yields and harvest volumes for influenza vaccines, as well as for other vaccines and viral vectors, downstream processing (DSP) is becoming an important factor in the race for higher overall productivity and decreased cost of goods. The general aim of DSP is the recovery and purification of biological products from process- and product-related impurities. Process-related impurities might originate from cell culture reagents and additives (e.g., antibiotics, bovine serum albumin and Benzonase ® [Merck KGaA, Darmstadt, Germany]), from the purification process (e.g., extractables and leachables in chromatography), or from the cell substrate (e.g., host cell protein, nucleic acids, proteoglycans and glycosaminoglycans). Examples for virus particle-related impurities include free envelope...