The use of disposable cell culture systems for the manufacturing of biological products in mammalian cells is advantageous
because it facilitates minimization of necessary validation efforts, as well as circumvention of up-front sterilization and
subsequent cleaning steps. For research-scale applications, culture systems typically used are tissue culture flasks, roller
bottles, or spinner bottles, and 1 to 50 mg of proteins in total volumes up to 2 L are produced (Table 1). In biopharmaceutical
development or for manufacturing of antibody-based diagnostics, a scale-up of production to reach protein yields of 50 to
1,000 mg is often necessary. To meet these increased protein yields, two alternative routes might be considered. Either increase
the culture volume, or switch to a technology that yields product in a more concentrated form.
For volume scale-up, increasing the number of cell-culture disposables is cumbersome because handling-time and space requirements
increase accordingly, inevitably resulting in higher manufacturing costs. A more economic solution is provided by bag-based
disposable systems, available in working volumes of up to 500 L, providing an alternative to stainless steel bioreactors.
However, working with bag-based bioreactors requires capital investment in specific equipment and trained personnel.
Another possibility is to use disposable two-compartment bioreactors that allow production of recombinant proteins in a highly
concentrated form. The two-compartment technology has been widely adopted in recent years as it does not require any additional
investment in specific equipment and can be easily handled by staff experienced with standard cell-culture systems.
The first part of this article describes two-compartment cell cultivation, for readers unfamiliar with it. Part two presents
a cost analysis for production of monoclonal antibodies (MAbs) using two-compartment technology that many laboratories have
successfully employed for production of MAbs in the milligram-to-gram range. The production costs associated with the most
widely used two-compartment system are compared to the costs of conventional production with roller bottles or with a stirred
bioreactor. The data presented are based on results obtained from in-house experiments at INTEGRA Biosciences AG, from customer
surveys, and supported by figures from published literature.
TWO-COMPARTMENT CELL CULTIVATION
In its simplest form, two-compartment cultivation occurs when cells grow inside dialysis tubing placed in a culture bottle
filled with medium. Because of the semi-permeable properties of the tubing, small nutrient molecules such as glucose or glutamine
can freely diffuse to the cells, while toxic catabolites are continuously removed from the cells by diffusion in the opposite
direction. Trapped inside the tubing, the cells are optimally supported and can grow to high densities.
The first commercially available two-compartment systems were hollow fiber bioreactors (HFBs), based on a bundle of hollow
fibers embedded in a disposable plastic cartridge. The culture medium is continuously perfused through the hollow fibers while
the cells reside in the space surrounding the fibers. The walls of the hollow fibers are semi-permeable like a dialysis membrane
so nutrients and metabolic waste products can freely diffuse to and from the cells. HFBs require specific equipment, consisting
of a pump to maintain medium flow and provide gas exchange. An overview of HFBs was given by Jackson, Trudel, and Lipman in
1999, but several systems they described have disappeared from the market as they proved too expensive and too cumbersome
to use.1 This was especially true for a production scale smaller than one gram, whereas HFBs are still used for a higher scale (Table