Biology Reference
In-Depth Information
Figure 9. Correlation between number of cells and amount of product produced. Solid
diamonds=cell number profile; hollow diamonds = product amount profile.
of nutrients to the cells, and rHuEPO and metabolic waste products from the
cells must be carefully considered in the design of the process. A commercial
production lot from adherent cultures typically entails using many small pro-
duction vessels; the challenge of such a process for commercial scale produc-
tion is to demonstrate equivalent control (i.e., monitoring) of each of the mul-
tiple production vessels. The degree of control required is imposed to achieve
the growth and productivity performance from each production vessel. After
product is produced, it is separated from the cells in the harvest process. Since
cells are attached to the solid substrate, harvesting the rHuEPO product in the
liquid conditioned medium is operationally straightforward and involves pour-
ing off or decanting the liquid before volume reduction and purification.
For suspension cultures, the number of cells itself generally limits the pro-
ductivity of the production. To increase production, the number of cells per
unit volume (i.e., cell density) may be maximized,and/or the volume of cul-
ture may be maximized. To maximize the cell density, limiting nutrients with-
in the culture environment are identified and supplements are added to the cul-
ture. The medium is sufficiently enriched to support the maximal number of
cells. To maximize the culture volume, a larger scale of production vessel may
be used. Increasing the scale of production for suspension cultures within a
single vessel is fairly straightforward. Both cells and product are distributed
homogeneously in well-stirred reactors so that the growth and production per-
formance within each volume of liquid is consistent. The volume of liquid may
be increased as long as homogeneity is achieved (i.e., mixing is adequate).
Stirred tank reactors for suspension cultures of mammalian cells typically
