High-Density Cytostat Cell Cultures with Homeostasis of Glucids and Amino Acids

Abstract

Continuous production of biologicals from high-density cultures requires that cell physiology be maintained in high-performance conditions for long periods. In the present paper, cell culture experiments are presented, where the bioreactor is kept in a growing state, even though cell concentration is maintained in a fixed range by continuous cell removal. Sustained perfusion with culture medium allows the cytostat to operate at 10⁷cells/ml, provided enough substrates are supplied to the bioreactor. Therefore a closed-loop system is presented whereby the feeding rates for glucids and amino acids are enslaved to their residual concentrations inside the bioreactor. For biochemical analyses, a sample processor ensures intermittent sampling of ultrafiltered supernatant from the bioreactor. On-line determination of amino acids and ammonia is achieved by reversed-phase HPLC after derivatization with 9-Fluorenylmethyl chloroformate. Glucids and organic acids are on-line determined by isocratic HPLC on a size exclusion /ion exclusion column. The actual values for glucids and amino acids are used to automatically adapt their supply to the culture. The resulting homeostasis of cells, glucids and amino acids is found to be helpful in sustaining cellular metabolism for several weeks in so-called high-density animal cell cultures.