Development of suspensions adapted Vero cell culture process for production of viruses

Vero cells are considered as the most widely accepted continuous cell line by the regulatory authorities (such as WHO) for the manufacture of viral vaccines for human use. The continuous Vero cell line has been commercially used, after propagation on microcarriers, for the production of rabies, polio, enterovirus 71 and hantaan virus vaccines. Vero cell culture technologies are also explored for productions of many more viral vaccines over the last two decades. The growth of Vero cells is anchorage-dependent, and cells need to be dissociated enzymatically or mechanically for the process of subcultivation. This process is labor intensive and complicated in process scale-up. Adaptation of Vero cells to grow in suspension will simplify subcultivation and process scale-up significantly. Here we report on the adaptation of adherent Vero cells to grow in suspension using a serum-free and animal component-free medium developed in-house. The maximum cell density and cell doubling time of the suspension adapted Vero cells in batch culture grown in the in-house developed medium were similar to or better than what was observed for the adherent Vero cells grown in commercial media. The growth of suspension adapted Vero culture was successfully scaled up to 3 L bioreactor. The Vero cells from various stages (both adherent and adapted) were tested for their authenticity using a Short Tandem Repeat (STR) analysis. The testing result indicates that all Vero cell samples have 100% concordance with the Vero DNA control sample, indicating the suspension adapted cells maintained their genetic stability. Productions of vesicular stomatitis virus (VSV) and influenza virus in adherent culture and suspension adapted culture were compared, showing the suspension adapted Vero cell retained similar viral productivity. The volumetric productivity of VSV in the suspension culture was even higher, and was further increased by almost 200 times when culture was infected at higher cell density and with medium replacement before the virus infection. In contrast, the VSV production decreased when the adherent culture was infected at higher cell density. Additional process development revealed that the maximum cell density in batch culture was doubled, reaching 6x106 cells/mL, when the culture medium was replaced during the process of batch culture, which indicates potential for further increases in product titer