Investigations into the Fouling Mechanism of Parvovirus Filters During Filtration of Freeze–Thawed mAb Drug Substance Solutions

ABSTRACT Filtration to remove viruses is one of the single most expensive steps in the production of mAb drug products. Therefore, virus filtration steps should be fully optimized, and any decline in flow rates warrants investigation into the causes of such membrane fouling. In the current study, it was found that freezing and thawing of a mAb bulk drug solution caused a substantial decrease in viral filter membrane flow rate. Freezing and thawing also caused formation of aggregates and particles across a broad size range, including particles that could be detected by microflow imaging (≥1 μm in size). However, removal of these particles offered little protection against flow rate decline during viral filtration. Further investigation revealed that trace amounts of aggregates (ca. 10 −6 of the total mass of protein in solution) approximately 20–40 nm in size were primarily responsible for the observed membrane fouling.