ENHANCED ANTIBODY-PRODUCTION ASSOCIATED WITH ALTERED AMINO-ACID-METABOLISM IN A HYBRIDOMA HIGH-DENSITY PERFUSION CULTURE ESTABLISHED BY GRAVITY SEPARATION

A high density hybridoma perfusion culture was established by separating and recycling cells from the product stream to the reactor using a simple external sedimentation-based separator - an inclined modified Erlenmeyer flask. After 3 weeks, when the optimal perfusion rate of 1.0 day-1 had been reached, viable cell density stabilized at around 10 X 10(6) cells ml-1, a level five times that obtained by simple batch culture. The efficiency of the separator was enhanced by cell flocculation. Specific antibody productivity, which was initially 0.4 mug 1 X 10(6) cells-1 h-1, decreased to half that value while cell density was increasing, but recovered to the initial level when the culture finally stabilized at a high cell density. During the final phase, when viable cell density and specific antibody production were high, there was a marked shift in metabolism. Consumption of the two most important substrates for energy generation, glucose and glutamine, caused their broth concentrations to decrease to 1.5 mM and 1 mM, respectively, from input medium concentrations of 25 mM and 10 mM, respectively. At the same time there was an increase in the specific production of glycine and aspartate, their broth concentrations reaching 1.5 mM and 0.02 mM, respectively. We suggest that this shift in metabolism results in enhanced production of ATP from glutamine. The specific glucose consumption and lactate production also indicate that there is a shift to more energy efficient metabolism. The mechanism whereby this leads to enhanced specific antibody production remains to be elucidated. Nevertheless, the combination of high cell density and enhanced productivity obtained with the present perfusion culture resulted in a high monoclonal antibody production - 100 mg l-1 d-1.