Optimization of virus yield as a strategy to improve rabies vaccine production by Vero cells in a bioreactor

To improve rabies vaccine production by Vero cells, we have developed a strategy based on high cell density culture and optimization of virus yield. We have first optimized cell growth in spinner flask using a Taguchi's L8 experimental design. We analyzed the effects of the following factors: initial glucose and glutamine concentrations, Cytodex 1 concentration and the regulation of glucose level at 1 g l−1. We have also investigated the effect of the following factor interactions: Cytodex 1 concentration/glutamine concentration, Cytodex 1 concentration/glucose concentration and glucose concentration/glutamine concentration.Statistical analysis of the collected data pointed to the initial glucose concentration, the regulation of glucose level at 1 g l−1 and the interactions between Cytodex 1 concentration/initial glucose concentration and Cytodex 1 concentration/initial glutamine concentration as the parameters that affected cell growth.Using the optimal conditions determined earlier, we have studied Vero cell growth in a 7-l bioreactor and in batch culture, and obtained a cell density level equal to 3.6 ± 0.2 × 106 cells ml−1. Cell infection with rabies virus (LP 2061/Vero strain) at a multiplicity of infection (MOI) of 0.3 using M199 medium supplemented with 0.2% bovine serum albumin (BSA), yielded a maximal virus titer equal to 8 ± 1.6 × 107 Fluorescent Focus Units (FFU) ml−1.We have also studied Vero cell growth in a 7-l bioreactor using recirculation as a perfusion culture mode during cell proliferation step and perfusion for virus multiplication phase. In comparison to batch culture, we reached a higher cell density level that was equal to 10.1 ± 0.5 × 106 cells ml−1. Cell infection under the conditions previously indicated, yielded 14 l of virus harvest that had a virus titer equal to 2.6 ± 0.5 × 107 FFU ml−1. The activity of the inactivated virus harvest showed a protective activity that meets WHO requirements.