Improved Production of Retroviral Vectors Under Serum-Free Conditions for the Application of Gene Therapy

The influence of serum on the production of retroviral vectors by the HT1080 human fibrosarcoma-derived packaging cell line FLY-RD18 was investigated. A 5-fold increase in the vector titre was observed under serum-free condition, as compared to medium supplemented with 10%foetal calf serum. The increase of vector production under serum-free condition was accompanied by a dramatic reduction of the Supernatant protein content, leading to much better prospect for further vector concentration and purification. Serum had a negative and dose-dependent effect on virus titre, while it affected neither cell growth nor virus stability and infectivity. An extracellular protease activity was found to enhance the retroviral production. The inhibition of protease activity by serum protease inhibitors can explain the negative effect of serum on vector production.