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
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 1).