The original cell substrates used to produce biologicals (such as Polio Vaccine) were primary cells (ie not passaged in tissue culture). There are, however, some disadvantages with using primary cells including the necessity to continually source the cells from animals and, as a consequence of time restraints, the amount of testing that can be performed on these cells is limited .

In the 1960s diploid fibroblast (human) cells lines were developed for vaccine manufacture. These cell lines have a finite lifespan when passaged in tissue culture. More recently, biotechnology products have relied on continuous cell lines to produce biopharmaceuticals. The advantage of continuous cell lines is that they are immortalised and once established can replicate on an ongoing basis. This allows for a constant source of cell and also for reproducible and safe cell substrates by the establishment of cell banks and their exhaustive testing for adventitious agents.

Cell banks form the foundation for most biological and biopharmaceutical products. For all therapies which rely on a cell line to either produce a recombinant protein, act as a live viral vector or are the bacteria used to manufacture a vaccine; the cell bank is the foundation of the product. No wonder the cell lines used to generate the cell bank and all steps in the process to make the expression system are scrutinised by the regulatory authorities.

The cell bank is comprised of two parts: the Master Cell Bank (MCB), which is created first, and the Working Cell Bank (WCB) which is generated from the MCB. Cell Banks may be comprised of bacteria, yeast, virus, insect or mammalian cells.

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