Wave microcarrier cultivation of MDCK cells for influenza virus production in serum containing and serum-free media

Abstract

A process for equine influenza virus vaccine production using a microcarrier system (Cytodex 1) in a 2 L Wave bioreactor is described. Growth of Madin Darby canine kidney (MDCK) cells in serum containing GMEM medium (SC) is compared to growth in serum-free Ex-Cell MDCK medium (SF) without washing steps and medium exchange before infection. Cultivations with microcarrier concentrations of 2 and 4 g/L for both media are shown. Metabolic data from carbon and amino acid metabolism are discussed. Additionally, in roller bottle experiments the influence of multiplicity of infection (moi) and trypsin concentration on the HA value was investigated. Analysis of HA and TCID 50 at 37 °C showed a stable HA of maximum 2.6 log HA/100 μL for 2 weeks. Peak TCID 50 titers of 10 7.7 viruses/mL were achieved 20 h post infection, but infectivity was below detection limit after 150 h. Cell attachment onto microcarriers under serum-free conditions was improved by Ca 2+ addition and by cell harvesting without trypsin using only an EDTA/PBS solution. For the wave cultivation maximum virus titers of 2.3–2.6 log HA units/100 μL were reached from infection with a moi of 0.05. However, in SF medium pH dropped to less than pH 6.8 which resulted in lower HA titers of 1.7 log HA units/100 μL. For the higher microcarrier concentration (4 g/L) medium exchange steps (500 mL) were needed for both media. Omission of the washing step and medium exchange before infection in SF medium clearly simplified the influenza production process; however, for higher virus yields a better pH control of the wave bioreactor would be required. Higher cell densities (2.8 × 10 6 cells/mL for 2 g/L microcarrier) and better attachment compared to stirred tank bioreactors showed, that the wave bioreactor is a good alternative to stirred tank processes for expanding production capacities in case of a pandemic.