Correlation of specific oxygen uptake rates and cell cycle duration of adherent mammalian cells in a large-scale microcarrier system

The production of vaccines using mammalian cell culture is a major application in biotechnology. As an example, we investigate a production process for influenza vaccines produced in adherently growing mammalian MDCK cells [Genzel et al., 2004]. The process consists of a cell growth phase with a duration about 96 h followed by a virus replication phase, which requires about 72 h. Typically, cell numbers and various metabolite concen-trations were determined. In addition, flow cytometry [Darzynkiewicz et al., 1997] was used to determine the cell cycle states 'G0/G1', 'S' and 'G2/M'. Also, oxygen uptake rates during the cell growth phase were monitored. Typically, local maxima in the oxygen uptake rates during cell growth could be observed. Ramirez et al., 1990 suggested that the specific oxygen uptake is a function of cell cycle. Therefore, we assume that the distance between these observed maxima in the oxygen uptake rate could be correlated with the duration of a complete cell cycle. Reported doubling times of MDCK cells are about 18 hours. Here, we present a strategy to determine the duration of cell cycle for adherent mammalian cells by on-line monitoring of the oxygen uptake rate. A simple mathematical model is used to describe the cellular growth kinetics based on flow cytometry data taking into account that elevated extracellular lactate levels increase the duration of mammalian cell cycle. Darzynkiewicz et al., 1997. DNA content measurement for DNA ploidy and cell cycle analysis, in: Robinson, JP; Darzynkiewicz, Z; Dean, PN; Hibbs, RA; Orfao, A; Rabinovitch, PS; Whelless, LL (Eds.): Current protocols in cytometry, Wiley & Sons, Unit 7.5 Genzel et al., 2004. Metabolism of MDCK cells during cell growth and influenza virus production in large-scale microcarrier culture. Vaccine; 22(17-18), 2202-2208 Ramirez et al., 1990. Cell cycle- and growth phase-dependent variations in size distribution, antibody productivity, and oxygen demand in hybridoma cultures. Biotechn. Bioeng.; 36(8) 839-84