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The concept of the feeding strategy was to minimise the formation of inhibiting metabolites and to increase the yield of monoclonal antibodies in fed-batch cultures of hybridoma cells by a balanced supply of substrates. A process control system based on ®eldbus technology was used for monitoring and control. External program routines were implemented to control dissolved oxygen (DO) and to calculate the oxygen uptake rate (OUR) and cumulative oxygen consumption (COC) simultaneously. A concentrated feed solution was supplied according to the off-line estimated stoichiometric ratio between oxygen and glucose consumption (GC). Feeding was initiated automatically when the OUR decreased due to substrate limitation. The antibody concentration increased three-fold compared to the conventional batch culture by applying this strategy. But it was not possible to avoid inhibition by ammonia during the fed-batch phase. This was accomplished by the use of a dialysis membrane. Dialysis fed-batch cultures were performed in a membrane dialysis reactor with a`nutrient-split' feeding strategy, where concentrated medium is fed to the cells and toxic metabolites are removed into a buffer solution. This resulted in a ten-fold increase of the antibody concentration compared to the batch. Amino acid concentrations were analysed to identify limiting conditions during the cultivation and to analyse the performance of the nutrient supply in the fed-batch and dialysis fed-batch.

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While fed-batch suspension culture of animal cells continues to be of industrial importance for the large-scale production of pharmaceutical products, existing control concepts are still insufficient. The present paper illustrates the advantages and disadvantages of different fed-batch strategies, including fixed-feed trajectories, control via OUR (oxygen uptake rate) (stoichiometric feeding), a priori determination of feed trajectories based on a kinetic model and the model-based adaptive OLFO (open-loop-feedback-optimal) control strategy. A recommendation as to which control strategy should be used for a specific process has to consider the respective process. For an established process with a well characterized and stable production cell line, probably the application of a fixed feed trajectory should be recommended. An adaptive, model-based control strategy could be the method of choice during cell-line development or for rapid production of small amounts of product for clinical trials, owing to its universal character and because it does not require intensive process development.

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