Online measurement and balancing of dissolved carbon dioxide in cell culture technology

Product yields of biologicals such as monoclonal antibodies, recombinant proteins and vaccines produced in mammalian cell culture have to be improved constantly to cope with increasing demands and process economics. As an example, we investigate an influenza vaccine production process with adherently growing Madin Darby canine kidney cells (MDCK) [1]. Besides typical online process variables such as pH and pO2 the concentration of dissolved carbon dioxide pCO2 is an important process parameter for monitoring bioprocesses. Elevated levels of dissolved carbon dioxide and osmolality can influence the intracellular pH, enzyme kinetics and growth of cells [2]. Miller and co-workers also reported on the influence of elevated dissolved carbon dioxide levels on the glycosylation of the recombinant protein tPa [3]. Cell culture medium is complex and often contains additives such as serum or hydrolysates. Therefore, the use of an off-gas analysis is to be seen critically, as the prerequisite of the Henry law of heavy diluted liquid is not given in every case. To monitor the concentration of dissolved carbon dioxide the Fiber Optic Chemical sensor YSI 8500 (YSI, Yellow Springs OH, US) [4] can be used. Here, we present results of dissolved carbon dioxide measurements during an influenza vaccine production process and an approach to balance dissolved carbon dioxide using (de)gassing kinetics and dissociation reactions. Aim is the determination of the carbon dioxide evolution rate (CER) of the cells. Problems and limitations of this approach will be discussed. [1] Genzel et al., 2006. Wave microcarrier cultivation of MDCK cells for influenza virus production in serum containing and serum-free media. Vaccine; 24 (2006) 6074-6087 [2] V. de Zengotita, A. Schmelzer, W. M. Miller. 2002. Characterization of Hybridoma Cell Response to Elevated pCO2 and Osmolality: Intracellular pH, Cell Size, Apoptosis, and Metabolism. Biotechnol Bioeng.; 77(4):369-80. [3] R. Kimura, W. M. Miller. 1997. Glycosylation of CHO-Derived Recombinant tPa Produced under elevated pCO2. Biotechnol. Prog. 13, 311-317 [4] R. Pattinson, J. Swany, B. Mendenhall, C. Hwang, B. Frohlich. 2000. Measurement and Control of Dissolved Carbon Dioxide in Mammalian Cell Culture Process using an in-situ Fiber Optic Chemical Sensor. Biotechnol. Prog. 16, 769-77