Optimization of Reovirus Production from Mouse L-929 Cells in Suspension Culture

Reovirus serotype 3 Dearing (T3D) has shown potential as a novel cancer therapy. To support the increasing demand for reovirus, a two-stage perfusion mode scheme is proposed for cell growth and reovirus production. Mouse L-929 cells were used as the host for reovirus infection due to their ability to grow well in suspension culture. Several L-929 cell growth and reovirus infection characteristics were investigated and optimized in spinner flask batch cultures. For the growth of L-929 cells, a balanced nutrient-fortification of SMEM medium increased the maximum cell density by 30%, compared to normal SMEM; however, ammonia and lactate accumulations were found to inhibit further cell growth. For the production of reovirus, ∼90% increase in viral yield resulted when the infection temperature was reduced from 37 to 33°C. Infectious reovirus particles were shown to be stable in conditioned medium at 37 and 33°C. The final virus titer was dependent on the multiplicity of infection (MOI) and the host cell density at the time of infection. A combination of an MOI of 0.1 pfu/cell and an initial host cell density of 1.0 × 10⁶ cells/mL in fortified medium resulted in a maximum virus titer of (4.59 ± 0.16) × 10⁹ pfu/mL and a specific yield of (2.34 ± 0.08) × 10³ pfu/cell. At an optimal harvest time of the infection process, 99% of the virus was associated with the cellular debris. Finally, the presence of 5.0 mM ammonia in the culture medium was shown to seriously inhibit the reovirus yield, whereas lactate concentrations up to 20 mM had no effect.