Use of <scp>LC</scp>‐<scp>MS</scp> to characterize host cell protein removal during depth filtration

The removal of host cell proteins (HCPs) is crucial in biopharmaceutical production, as residual impurities can impact product safety and efficacy. While a number of studies have demonstrated that depth filtration can provide significant HCP removal, there is little information on its effectiveness in removing specific HCPs. This study examines the application of liquid chromatography-mass spectrometry (LC-MS) to track HCP removal during depth filtration, providing a detailed analysis of HCP behavior with two commercial depth filters. Our findings reveal significant variability in HCP breakthrough behavior, with transmission patterns showing minimal correlation with either the protein isoelectric point or hydrophobicity, highlighting the unique behavior of individual HCPs. Both the X0SP and X0HC depth filters achieved almost complete removal of Lipoprotein Lipase, and the X0SP filter also effectively removed Lysosomal Acid Lipase (LAL), both known to degrade polysorbate in monoclonal antibody formulations. However, neither filter provided significant removal of Alpha-enolase, Carboxypeptidase D, Glutathione S-transferase, or Phospholipase B-like 2. The X0SP filter showed equal or better removal for 18 out of 20 problematic HCPs, with greater HCP removal seen at lower conductivity. This work provides a detailed framework for understanding and optimizing depth filtration processes, offering insights into the effectiveness of depth filters for removal of problematic HCPs.