Advances in fermentation and cell culture techniques have greatly increased the titers of target proteins in culture fluid. This increase in upstream efficiency has led to a bottleneck in downstream processing at the cell-harvest stage. Scale up of current tangential flow filtration (TFF) systems has not been successful in terms of efficiency and economics.
Cell harvesting, or clarification, is an important process in nearly all downstream purifications of biotech-based products. When the product is internal to the cells, cell harvesting is used to decrease the liquid volume of cells to be processed in the product extraction steps. An example of this process type is the isolation of inclusion bodies from E. coli lysate prior to solubilizing the inclusion body product.
When the product is extracellular, cell harvesting is used to separate the product from the cells and cellular debris. An example of this process type is the isolation of an extracellular antibody from mammalian cell culture.
Commercially available methods for cell harvesting include TFF and the combination of centrifugation with depth filtration. Current installations of TFF systems, as well as centrifugation offer significant opportunities for improvement.
TFF is a well-established technology for cell harvesting. Traditional TFF modules for biopharmaceutical applications use flat-sheet formats that are assembled into cassettes or hollow fibers that are assembled into modules. Originally designed with a small membrane area for laboratory filtrations, cassette and hollow-fiber systems were enlarged to meet pilot- and production-scale operations without consideration of the fluid flow dynamics required for the larger membrane incorporated in the scaled-up processes.
Overall, the advantages of TFF include relatively low capital costs and the ability to reuse the filter modules. However, as companies scaled up traditional TFF formats, they encountered low yield, short filter life, and inconsistent results. Reasons for the low yield and decreased performance included filter clogging during the process.