Manufacture of viral vectors

Master and working banks of both the viral vector and the animal cell line will have been constructed during the drug development process (see Chapter 4). Manufacture of a batch of vector, therefore, will be initiated by the culture of packing cells in suitable animal cell bioreactors. The 

CH14 NUCLEIC-ACID- AND CELL-BASED THERAPEUTICS 

---

Viral vector manufacture for therapeutic purposes involves initial viral propagation in appropriate animal cell lines, viral recovery, concentration, purification and formulation. A generalized manufacturing scenario for adenoviral-based vectors is outlined in Figure 14.7. The manufacture of alternative viral vectors likely follows a substantially similar approach. 

The issue was one of getting the DNA into a cell and this gave rise to the use of viral delivery systems and bacterial plasmid DNA (pDNA) vectors. pDNA vectors are useful since they are much safer to manufacture on a large scale, inexpensive, and easily customized—apart from being safer for the patient. However, the down side is that these systems are poorly immunogenic although, as noted above, this might be improved by the addition of an appropriate adjuvant. 

The second component of a successful clinical manufacturing program is appropriate quality assurance systems for the production of cell or viral banks, raw materials, in-process materials, and final product. Much has been written about the production and testing of cell and viral banks for use in manufacturing. Both FDA guidelines and other reference information are available (http // www.fda.gov.cber/guidelines.htm http //www.ich.org, http //www. emea.eu.int). The production of AAV vector batches for use in clinical trials should use qualified cell, viral, and/or plasmid banks as appropriate. Documentation on the source materials for these banks is also crucial in assuring the quality and safety of the clinical trial materials. 

On the other hand, from the technological point of view, several barriers have already been overcome, allowing production of viral or plasmid DNA vectors at a cost that enables clinical application. Safe manufacturing processes are already available, and the production capacity for these systems is easily accessible worldwide. 

The alternative approach is to use non-viral vectors, such lipid-based, peptide-based and polymer-based delivery systems, as described in detail in Chapter 14. Liposomes are relatively easy to manufacture, are generally non-toxic and are devoid of the capability to cause an infection (see Section 5.3.1). However, a number of limitations are associated with their use. For example, it is difficult to direct liposomes to a particular type of cell. Liposome/DNA complexes which may be internalized by the target cells are... 

Among non-viral vectors, the lipoplex and polyplex systems [69,70], in which cationic Hpids and polycations, respectively, associate with DNA through an electrostatic interaction, are most widely studied for both in vitro and in vivo transfection. Their assets are that they can carry various size ranges of DNA, ease in manufacturing and mass production, a variety of chemical designs with smart fimctions, and their surface properties can be readily controlled by changing the charge ratio between the cationic polymer and DNA. 

---