(131e) Mechanisms of Protein and DNA Removal in Depth Filtration

The routine use of depth filtration for harvest clarification in bioprocessing is aimed primarily at removal of particulates. However, impurities such as host-cell proteins and DNA are also typically removed to a significant extent. This presentation will explore some of the mechanisms that contribute to such impurity clearance. For proteins, we have measured the adsorption of model and therapeutic proteins on different depth filter components and assessed the driving force for such adsorption. We have also used confocal microscopy to determine the distribution of different proteins on the different depth filter components. Although filter aids typically behave as cation exchangers, protein adsorption is more commonly dominated by the binder, which has some anion-exchange character. For DNA, we have used covalent labeling of DNA and visualization by confocal microscopy of the extent of penetration of the retained DNA on depth filters. This has allowed resolution of retention by adsorption from retention by size-based filtration.