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Effects of pH and Ionic Conditions on Microfiltration of Mammalian Cells: Combined Permeate Flux Enhancement and Mab Purification Capabilities

Jonathan Karl Romero, Philippe de Vilmorin, and James Chrostowski. Process Development Engineering, BiogenIdec Inc, 15 Cambridge Center, Cambridge, MA 02142

The drive for generating increased titer cell-culture processes for producing monoclonal antibodies has placed demands on cell harvesting and downstream purification operations for removing cells and impurities from large-scale bioreactors. Previous work has successfully demonstrated the control of fermentation broth pH during the production of antibiotics from bacteria to precipitate the microorganism and assist in contaminant removal for improving harvest operation robustness using cross-flow microfiltration. However, there is limited understanding of the effects of harvest conditions (pH, ionic strength/composition) on the MF operation applied to mammalian cell systems for the production of monoclonal antibodies. The objective of this work is to present a framework for describing the performance of microfiltration systems for both cell and impurity removal using controlled harvest conditions and MF process data to illustrate the key phenomena governing the behavior of these systems. Settling experiments of unclarified harvest media were performed at various ranges of pH and ionic conditions with turbidity, product titer, and impurity assays performed on the supernatant. Data demonstrate a drop in both supernatant turbidity and DNA impurity levels at low pH, indicative of cell precipitation and selective DNA precipitation of this impurity from the soluble mAb product under these conditions. MF clarification of conditioned media under the same feed conditions showed improved flux performance and reduced transmembrane pressure profiles along with reduced permeate DNA levels. In addition, offline settling experiments provide an appropriate framework for the design and optimization of cross-flow microfiltration systems for processing mammalian cell culture broths for production of therapeutic mAbs.