We’ve seen a number of different systems used to generate the water and there is no one easy
answer. Certainly the water quality for, let’s say, an E. coli fermentation can be different, probably
a lower quality than you’d need for a mammalian cell culture. However, having said that, you
won’t find that Q7A specifically requires Purified Water, as defined in USP, or WFI, as defined in
USP. Certainly, the question about “softened” water, depending upon the cell line that’s being
used and the process, if that would meet the Purified Water requirements that could be
acceptable. Again, you’d have to take a look at the process, at the intended use of the product,
and at what point in the process you use a higher-grade of water. The same is true for WFI.
Some firms use, essentially, ultra filtration to produce water that goes into fermenters.
Technically, that doesn’t meet the requirements for USP quality water. However, if you look at the
specifications, the testing that’s done, it certainly could meet the USP specs. Certainly for early
process stages, if it’s WFI-quality water that’s being produced by UF, there should not be an
objection to it.
The other way to look at this is to look at the product and look at the process, and see how
effectively you can remove Endotoxin from the product by downstream processing. For example,
if you’re going to make a recombinant product using E. coli, (which is the organism in which most
microbially produced products are made), E. coli is four percent Endotoxin by weight. So, it’s
pointless to start off an E. coli fermentation with WFI. That is not necessary, and, in general,
deionized water works just fine for most E. coli fermentations.
The general rule is to use WFI for all cell culture fermentations. But, if you’re talking about cell
culture, especially serum-free cell culture, and you’re talking about relatively large molecules with
complex structures; you may not be able to remove Endotoxin from those kinds of products if they
creep into the process. The other consideration is that Endotoxin, itself, also can upset the
metabolism of mammalian cells in culture in ways that are unpredictable, which is another reason
to keep it away. Yet another reason is that serum-free cell culture leaves the cells without the
protection that serum proteins, like transferon, would normally provide it. The only way that you
can be reasonably certain that you’re going to be able to provide water of a high enough quality to
get consistently good results, in my experience, is to use WFI.
