This study reports the use of lactate dehydrogenase release to monitor changes in culture viability in flask culture and fixed bed, porosphere bioreactor systems. Lactate dehydrogenase release shows good agreement with increase in non-viable cell numbers and decline in glucose utilisation in flask cultures. Studies with the immobilised system show that lactate dehydrogenase release can detect loss of viability which is not always indicated by a decrease in glucose utilisation. The data show that culture viability in a repeated-feed-and-harvest system is influenced markedly by both a) the medium change regime itself and b) the use of an immobilised bioreactor compared to a flask system for the same medium change regime.

No abstract

Process intensity of fixed bed glass sphere culture systems is increased considerably by replacing solid glass spheres with open pore glass spheres. This technique demonstrates the possibility of having a system capable of both volumetric and cell density scale up and being suitable for substrate attached and suspension cells. The yields achieved for a number of attached cell lines (approximately 10(7)/ml) demonstrate an increase approaching one order of magnitude over solid glass spheres (approximately 10(6)/ml). Also suspension cells were successfully entrapped in the open pore structure with similar yields.

In this work a recombinant BHK21 clone producing a fusion protein with potential application in tumour target therapy was adapted to five different serum-free media (SFM) and to a protein-free medium (PFM). Only the PFM did not require a gradual adaptation to cell growth in the absence of serum. All tested SFM required a gradual adaptation (up to 35 days). For the majority of the SFM tested, cell specific productivity was not affected by the decrease in serum concentration during adaptation; however, cell growth was significantly affected by the serum decrease. Both cell growth and productivity were increased when PFM SMIF6 was used instead of the control medium. Long term measurements (approximately 100 days) of cell specific productivity for PFM and the two best SFM showed that productivity was maintained. This indicates the media capability to be used in long term production processes.

A comparison of cell yields and monoclonal antibody productivity from the same hybridoma has been made in a wide range of cell bioreactors including both batch and continuous perfusion cultures. The most productive systems were based on porous microcarriers in fixed and fluidised beds which can be operated with a high degree of efficiency and reliability from the physico-chemical engineering point of view. Further improvements should be possible by improving the physiological environment in dense cell cultures, as indicated by the preliminary studies that are described. These include experimental data showing the relationship between monoclonal antibody production rates with glucose, glutamine, ammonia, and oxygen levels in microporous beads. The results strongly indicate that perfusion processes that are scaleable in both volume and cell density can significantly reduce production costs. Manufacturers of biologicals from animal cells now have a choice between the proven batch-type processes and reliable perfusion systems based on microporous beads.