Increased production of human granulocyte-macrophage colony stimulating factor (hGM-CSF) by the addition of stabilizing polymer in plant suspension cultures

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a glycoprotein that stimulates the production of granulocytes, macrophages, and white blood cells. Secretion of human GM-CSF from cell suspension cultures of genetically modified tobacco has been facilitated using natural mammalian leader sequences. At the mid-exponential growth phase (day 4 after the initiation of cell suspension culture), GM-CSF was detected in the medium at a maximum concentration of 180 μg l^-1. However, the secreted GM-CSF was unstable in the medium, and rapidly degraded after day 5. In order to stabilize the secreted GM-CSF, three stabilizing polymers were tested, polyethylene glycol, polyvinylpyrrolidone and gelatin. Gelatin was the most effective in stabilizing the secreted GM-CSF. Following the addition of 5% (w/v) gelatin, the maximum GM-CSF concentration reached 783 μg l^-1, a 4.6-fold increase over control.