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The cell retention system XCell2 by Repligen is used for continuous biopharmaceutical production in perfusion systems. The device retains the cells while the media can be continuously replaced by fresh media, and the product can be continuously harvested. In addition, the device can be used to obtain very high cell densities in the bioreactor leading to high volumetric productivities. The XCell2 is an alternating tangential flow (ATF) device which uses hollow fibre membranes for cell retention and avoids fouling of these filters by alternating movement of the cell suspension and reducing the shear stress on the cells in comparison to a normal tangential flow filtration (TFF) device. Depending on the used hollow-fibre membranes, the XCell2 can be used with lab scale parallel multibioreactor systems (volumes of 300-1500 mL) or with small pilot scale reactor systems (volumes of 1 L to 10 L).
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Depending on the method, the system can be used for the following purposes:
Perfusion culture, continuous production: The classical use of ATF-perfusion cultures is the use of a stable cell line in perfusion continuous production of recombinant proteins. The device is connected to a bioreactor which is continuously supplied with fresh media, and the ATF device is continuously retaining cells from the harvest stream. The produced recombinant protein as well as the spent media is continuously harvested and the cell concentration in the bioreactor can be maintained on a high level through the use of the ATF device.
Perfusion culture, high cell density: The device can also be used to prepare a high cell density of a non-producing cell line, before the cells are transfected for transient production or infected for virus production. The high cell density before transfection/infection is only possible through the use of the ATF-device for cell retention and increased the volumetric productivity of the process.
High cell density inoculum preparation: Production fermenters need an inoculum of cells to start their production. The current trend for production of recombinant proteins tries to reduce the time the production fermenter needs to be used for the actual production before harvest. A high cell density inoculum of a stable cell line for recombinant protein production prepared by ATF-perfusion lead to significantly shorter production times in the fermenter. The ATF-device is fundamental to the generation of such high cell density inoculums.
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