Small-scale HFBs have been displaced by membrane-based two-compartment systems, which have proven to be more cost effective
and simpler to use. Currently, two systems are available: the two-compartment roller bottle miniPERM (designed by the German-based
In Vitro Systems & Services GmbH) and the static flask CELLine (INTEGRA Biosciences AG, Switzerland).1-4 As shown in Figure 1, the core element of the CELLine system is the cell compartment, which is formed by two different membranes
incorporated into the bottom of the cell-culture flask. The upper membrane separates the cell compartment from the medium
compartment and is made of a semi-permeable cellulose acetate sheet for exchange of metabolites between the two compartments.
The lower membrane is made of gas-permeable silicone and guarantees efficient oxygen and CO2 transfer between the cell compartment and the incubator. Because the cell compartment is only 2 to 3 mm thick, efficient
oxygenation is achieved by simple diffusion, hence avoiding the need for agitation and the resulting detrimental shear stress.
Table 1. Comparison of Different Disposable Cell Culture Systems for MAb Production (Modified after McArdle4)
As illustrated in Figure 1, cells and the secreted expressed proteins accumulate in the cell compartment, located at the
bottom of the flask, separated from the medium compartment by a dialysis membrane, indicated by a line of dashes (---) in
the diagram. Nutrients smaller than 10 kDa freely diffuse through this dialysis membrane, thereby sustaining cell growth.
Similarly, but in the opposite direction, toxic catabolites cross the dialysis membrane and are removed from the cells' surroundings.
Efficient gas exchange takes place through the gas-permeable silicone bottom of the cell compartment membrane, indicated by
a line of dots (···) in the diagram.
COST ANALYSIS FOR 200 mg MAb PRODUCTION
Due to the high reaction specificity of MAbs, the production scale necessary for research and development applications, for
in vitro diagnostics, or for quality control purposes does usually not exceed 1,000 mg. In the comparative analysis presented here
and summarized in Table 2, we consider the costs arising during production of 200 mg MAbs using either a CELLine 1000 or conventional
non-compartmentalized systems (roller bottles and a stirred bioreactor). Different production parameters need to be defined
according to the required yield and to the culture system used (listed in the upper section of Table 2). The production process
depends on productivity of the hybridoma clone used, i.e., on the amount of MAb produced per mL culture supernatant. In conventional
cultivation systems, the maximal hybridoma density achieved is approximately 106 cells/mL, and typical productivity values found in the literature are 0.01 to 0.05 mg/mL.1-4 It must be noted that productivity can be considerably inferior when using a "low secretor" clone, as is often the case
when productivity is not considered during clone selection. The other parameter influencing the production process is the
volume of produced supernatant. Concerning the roller bottle and the stirred bioreactor, a supernatant volume of 300 mL and
5,000 mL per culture vessel has been defined, respectively. When assuming a productivity of 0.04 mg/mL and a batch culture
protocol (i.e., one harvest per cultivation vessel), the volume of supernatant required to yield 200 mg MAb amounts to 5 L,
which requires the use of 17 roller bottles or one bioreactor run.
Figure 1. Schematic Representation of the Two-Compartment Set-up in a CELLine 1000 Bioreactor