Higher yields in influenza vaccine production using perfusion in high-density cell culture

To increase process yields for virus vaccine production in mammalian cell culture an increase in cell density is of prior interest. However, often a so-called "cell density effect" [1] results in high cell densities without corresponding increase in product. Typically, a lack of medium components or an accumulation of inhibitory compounds seems to be responsible for this effect and strategies to overcome it consist of discontinuous or continuous medium exchanges. Here, we present results obtained from perfusion cultivations of an influenza vaccine production process with adherent Madin Darby canine kidney cells (MDCK). The process consists of a cell growth phase and a virus replication phase [2]. Cultivations were performed with microcarrier concentrations up to 12 g/L (Cytodex 1) in serum-containing and in serum-free medium. Cell numbers on microcarriers at time of infection of 8.0 x 106 and 9.5 x 106 cells/mL, respectively, were achieved. During cell growth the perfusion rate was increased proportional to cell numbers from initially 0.04 h-1 to 0.2 h-1. During virus replication perfusion rate was set to 0.3 h-1. For comparison results of repeated batch strategies are discussed. The specific virus productivities remained constant compared to a standard process with microcarrier concentration of 2 g/L and cell numbers at time of infection of about 1.6 x 106 cells/mL. With the chosen perfusion strategy during cell growth and virus replication the "cell density effect" could thus be overcome. [1] Ferreira, T.B., Ferreira, A.L., Carrondo, M.J.T., Alves, P.M.; 2005. Effect of refeed strategies and non-ammoniagenic medium on adenovirus production at high cell densities. J. of Biotech. 119: 272-280 [2] Genzel, Y., Behrendt, I., König, S., Sann H., and Reichl, U.; 2004. Metabolism of MDCK cells during cell growth and influenza virus production in large scale bioreactors. Vaccine 22: 2202-220