Production of Oncolytic Measles Virus in Vero Cells: Impact of Culture Medium and Multiplicity of Infection

Oncolytic measles virus (MeV) is a promising anti-cancer treatment. However, the production of high titers of infectious MeV (typically 10⁷-10⁹ TCID₅₀ per dose) is challenging because the virus is unstable under typical production conditions. The objective of this study was to investigate how the multiplicity of infection (MOI) and different media-a serum-containing medium (SCM), a serum-free medium (SFM) and two chemically defined media (CDM)-affect MeV production. We infected Vero cells at MOIs of 0.02, 0.2 or 2 TCID₅₀ cell^-1 and the lowest MOI resulted in the largest number of infected cells towards the end of the production period. However, this did not equate to higher maximum MeV titers, which were similar for all the MOIs. The medium had a moderate effect, generating maximum titers of 0.89-2.17 × 10⁶, 1.08-1.25 × 10⁶ and 4.58-9.90 × 10⁵ TCID₅₀ mL^-1 for the SCM, SFM and CDM, respectively. Infection at a low MOI often required longer process times to reach maximum yields. On the other hand, a high MOI requires a large amount of MeV stock. We would therefore recommend a mid-range MOI of 0.2 TCID₅₀ cell^-1 for MeV production. Our findings show that SCM, SFM and CDM are equally suitable for MeV production in terms of yield and process time. This will allow MeV production in serum-free conditions, addressing the safety risks and ethical concerns associated with the use of serum.