Retrovirus producer cell line metabolism: implications on viral productivity

The production of retroviral vectors by human cell lines is still hampered by low titers making it relatively difficult to produce very large quantities of this vector of high interest for clinical gene therapy applications. Thus, to improve vector production, we studied the influence of different sugars alone or combinations of sugars on cell growth, vector titers, and metabolism of the producer cell. The use of fructose at 140 mM or a mixed medium (with glucose at 25 mM and fructose at 140 mM) improved the virus titer three- to fourfold, respectively, and the producer cell productivity by fivefold. The increase in the cell productivity was due to a 1.5-fold increase in the vector stability, the remaining increase being due to higher cell specific productivity. The increase in the productivity was associated with lower glucose oxidation and an increase in the lactate and alanine yield. In the mixed medium, an increase in fatty acids derived from the glucose was observed in parallel with a reduction of glutamate and glutamine synthesis via the tricarboxylic acid (TCA) cycle acetyl-CoA and alpha-ketoglutarate, respectively. Although the higher productivities were associated with severe changes in the glycolysis, TCA cycle, and glutaminolysis, the cell energetic status monitored by phosphocreatine and adenosine triphosphate levels was not significantly affected. The synthesis of fatty acids and phospholipids were enhanced in the fructose or mixed media and are possibly key parameters in retroviral vector production.