In such a case, the production unit will have to prove to the regulatory agencies that the new bank is the same as the original one. Since cell stability is also an important consideration, MWCB needs to be repeatedly subcultured and each generation checked for changes, if any.

It should also be checked, whether or not cellular material at the end of a production run, remains essentially the same as that in the MCB or MWCB.

It is also necessary to build up a volume of cultured cells, large enough to produce a product in large amounts necessary for an economically viable production unit. There are two ways to achieve this:

(i) by increasing the culture volume or

(ii) by increasing the concentration of cells in a reactor by continuous perfusion of fresh medium, so that the cells keep on increasing in number without the dilution of the medium.

Perfusion has a dual effect of supplying nutrients and removing potentially toxic metabolites.