Sources and upstream processing - Pharmaceutical Biotechnology: Concepts and Aapplications - page 130

composed of a mixture of growth factors, hormones and metabolites typically found in serum) is
required as a source of often ill-defi ned growth factors required by some animal cell lines.
The media constituents, several of which are heat labile, are generally dissolved in purifi ed
water and fi lter sterilized into the pre-sterile animal cell reactor. Reactor design (and operation)
differs somewhat from microbial fermentations mainly with a view to minimizing damage to the
more fragile cells during cell culture ( Figure 5.9). Although the generalized reactor design pre-
sented in Figure 5.9 is commonly employed on an industrial scale, alternative reactor confi gura-
tions are also available. These include hollow-fi bre systems and the classical roller bottle systems.
Roller bottles are still used in the industrial production of some vaccines, some EPO products and
growth-hormone-based products. Roller bottles are cylindrical bottles that are partially fi lled with
media, placed on their side and mechanically rolled during cell culture. This system is gentle on
the cells, and the rolling action ensures homogeneity in the culture media and effi cient oxygen
transfer. The major disadvantage associated with applying roller bottle technology on an industrial
scale is that many thousands of bottles are required to produce a single batch of product.
Different animal cell types display different properties pertinent to their successful culture.
Those used to manufacture biopharmaceuticals are invariably continuous (transformed) cell lines.
Such cells will grow relatively vigorously and easily in submerged culture systems, be they roller
bottle or bioreactor based.
Unlike transformed cell lines, non-continuous cell lines generally:

• display anchorage dependence (i.e. will only grow and divide when attached to a solid substra-

tum; continuous cell lines will grow in free suspension);

• grow as a monolayer;

• exhibit contact inhibition (physical contact between individual cells inhibits further division);

• display a fi nite lifespan, i.e. die, generally after 50-100 cell divisions, even when cultured under

ideal conditions;

• display longer population doubling times and grow to lower cell densities than continuous cell

lines;

• usually have more complex media requirements.

Many of these properties would obviously limit applicability of non-continuous cell lines in
the industrial-scale production of recombinant proteins. However, such cell types are routinely
cultured for research purposes, toxicity testing, etc.
The anchorage-dependent growth properties of such non-continuous cell lines impacts upon how
they are cultured, both on laboratory and industrial scales. If grown in roller bottles/other low-vol-
ume containers, then cells grow attached to the internal walls of the vessel. Large-scale culture can
be undertaken in submerged-type vessels, such as that described in Figure 5.9b in conjunction with
the use of microcarrier beads. Microcarriers are solid or sometimes porous spherical particles ap-
proximately 200 µm in diameter manufactured from such materials as collagen, dextran or plastic.
They display densities slightly greater than water, such that gentle mixing within the animal cell