Evaluation of the serum-free medium MDSS2 for the production of poliovirus on Vero cells in bioreactors

The serum-free medium MDSS2 (Merten et al., 1994), was used for cultivating Vero cells as well as for producing poliovirus (Sabin type 1) in static and in perfused microcarrier cultures. At slightly different growth rates of 0.0120/h and 0.0106/h, respectively, static cultures in serum-containing (SCM) and serum-free (SFM) medium produced titers of 10(6.75) and 10(6.67) TCID50 per 50 mu l; signifying a specific productivity of 0.89 and 1.07 TCID50/c. Serum-free bioreactor cultures of Vero cells on DEAE-dextran microcarriers at 6.25 g/l produced cell densities of about 1.5 x 10(6)c/ml. After infection with virus (multiplicity of infection (MOI) 0.1-0.3) titers of about 6.3 x 10(8) TCID50/ml were obtained, signifying an average specific productivity of 7.1 TCID50/c.h. Although these values were 4 and 2 fold, respectively, higher than in classical resum-based production processes (Montagnon et al., 1981), a reference culture, for which cell growth was done in SCM and only virus production was done in SFM, produced 2 x 10(9) TCID/ml with an average specific virus production rate of 18.9 TCID50/c.h. The differences between the fully serum-free and our reference process were mainly due to physiological differences of cells grown in SCM and SFM and also due to strongly modified consumption kinetics after virus infection leading to limitations of one or several essential medium compounds, like glucose and amino acids. Avoiding these limitations by increasing the residual concentration of glucose, glutamine, histidine, and SH-amino acids, led to specific virus production rates (of about 17.9 TCID50/c.h.) comparable to those found in the reference virus production process. The optimisation of the production of the poliovirus (Sabin 1) will be described with respect to the modification of the medium composition.