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Abstract:
Since several years the adherent cell line E-FL (feline lung fibroblast) is used for production of mink enteritis virus (MEV) vaccine at commercial scale. Presently the industrial process is performed in roller bottles. For large-scale production this approach means high input of equipment and manpower connected with a comparatively high contamination risk. Additionally, monitoring and control of cultivation conditions is very limited compared to fully equipped bioreactors. Aim of our research project was the transfer of the existing production process from roller bottles into a microcarrier system (Cytodex 1) and the optimization with respect to virus yields. First experiments for characterization of growth and metabolism of E-FL on Cytodex 1 were carried out in spinner flask (250 mL-scale) using a minimal essential medium (MEM) with fetal bovine serum (FBS) and L-glutamine. Standard analytics included measurement of cell number, pH, pO2 and extracellular metabolites (glucose, lactate, glutamine, glutamate, ammonia). As these first experiments were successful, the process was scaled up into a 5 L stirred-tank reactor using 1 g/L Cytodex 1 and a starting cell number of 0,6-1105 cells/mL. After three days of cultivation confluence was reached with cell numbers of 7-9105 cells/mL. Using higher carrier concentrations and improved MEM the cell yield could even be increased to 1,5-2106 cells/mL. Alternatively, cultivation of E-FL on Cytodex 1 in a novel wave bioreactor was established. Advantages of this system are low costs and its safety and simplicity in use under GMP restrictions. Cultivations of E-FL in the wave bioreactor were as successful as in stirred-tanks regarding cell numbers, morphology and metabolic activities. Optimal parameters for virus propagation were investigated by parallel cultivation in small scale fermenters (500 mL) using different MOI and starting cell numbers. Based on these results further experiments for virus propagation in stirred-tank-(5 L-scale) and wave bioreactor (1 L-scale) were carried out. Both culture vessels are compared with respect to cell growth and virus yields. We are able to show that both types of bioreactors are suitable for use in MEV vaccine production process. It is expected that slight advantages of stirred tank in cell number are more than balanced by low costs and simple GMP-conform handling of the wave bioreactor.
