IMPROVED YIELDS OF THE EXTRACELLULAR DOMAIN OF THE EPIDERMAL GROWTH-FACTOR RECEPTOR PRODUCED USING THE BACULOVIRUS EXPRESSION SYSTEM BY MEDIUM REPLACEMENT FOLLOWING INFECTION

The extracellular domain of the epidermal growth factor receptor (EGFR ) was expressed using the baculovirus expression vector system. The ma ximum level of the EGFR extracellular domain secreted into the medium in Sf-9 (Spodoptera frugiperda or fall army-worm) cell batch culture w as approximately 2.5 mu g ml(-1). In order to increase this yield, a p rocess was developed that included the following sequence of steps: ba tch growth to maximum cell density, infection of the cells with recomb inant virus, and replacement of spent medium. By using this process, t he specific yield of recombinant protein, which in batch culture drops when infection is carried out at densities greater than 3 x 10(6) cel ls ml(-1), can be maintained at a maximum in cultures infected at dens ities of 10(7) cells ml(-1) or greater. The process, when applied to 3 -1 and 11-1 bioreactor cultures, allowed a maximum volumetric yield of triple the maximum value attainable in batch culture. Spent-medium an alysis indicates that medium replacement provides certain nutrients th at could otherwise be limiting for recombinant protein production.