Adaptation of Vero cells to chemically-defined suspension culture and implementation of a stirred tank reactor process for the production of oncolytic measles virus

Oncolytic measles virus (MeV) naturally targets cancer cells, inducing their lysis and stimulating anti-tumor immune responses. The high titers of infectious MeV for treatment (10 7 –10 9 TCID₅₀ per dose) are currently produced in adherent Vero cells, requiring microcarriers for dynamic cultivation, complicating both upstream and downstream processing, and limiting production scalability. To address these challenges, we adapted Vero cells to suspension growth in chemically defined medium (CDM). The growth, metabolism and suitability of these cells for MeV production were investigated under dynamic cultivation using shake flasks and stirred-tank reactors (STR) at different scales. We showed that the adapted Vero suspension cells grew to 1.5-fold higher densities in the STR [(3.26 ± 0.54) × 10 6 cells mL −1 ] compared to shake flasks [(2.16 ± 0.22) × 10 6 cells mL −1 ], which also reflected faster growth rates. Besides the importance of carbon & nitrogen sources in the medium (e.g. glucose, glutamine, pyruvate), we found that the pH level, the lactate concentration and the osmolality were critical process parameters for prolonged exponential Vero cell growth. Infected Vero suspension cells reached MeV titers >1.5 × 10 6 TCID₅₀ mL −1 faster than adherent Vero cells in both shake flasks and the STRs. Beyond oncolytic MeV production, these CDM-adapted Vero suspension cells may provide a promising basis for developing a production platform for other viruses, virus-like particles, and viral vectors.