Influence of Serum Concentration on Cell Growth and Retrovirus Production and Decay Kinetics

Abstract

It has been shown that serum has a negative dose-dependant effect on retrovirus production in human packaging cell lines. However, to date the long-term effect of reduced serum concentrations on cell growth and productivity has not been reported. In this study, the human packaging cell line, TEFLYRD, which produces the recombinant non-replication competent retrovirus, OB83, was used to examine the effect of serum on cell growth, virus production and virus decay kinetics. During batch culture, no significant difference was seen in the specific growth rate or the maximum cell density between 1% and 10% FCS but a two-fold increase in cell specific virus production was observed between 10% and 2.5% FCS. It was also shown that the rate of virus decay was greatest in 1% FCS but is a weak function of serum concentration. The long-term effect of reduced serum concentrations on cells cultured in either 2.5% FCS or 10% FCS, with daily medium replacement, was also evaluated. No substantial difference was seen in the final cell number, showing that cells were not affected by reduced serum concentrations. The mean daily virus titre was shown to be 42% higher in 2.5% FCS compared to 10% FCS. This difference was less than in batch culture, suggesting that virus production was related to cell growth rate. Finally, a packed-bed reactor was used to culture cells immobilised within Fibra-Cel{\texttrademark} discs to assess the potential for large-scale production. However, a low serum concentration had an adverse affect on cell viability and virus production in this system.