Quantitative Analysis Reveals Hitchhiking Drives Polysorbate Hydrolase Persistence Via Host Cell Protein–Antibody Interactions

Polysorbate‐degrading host cell proteins (HCPs) represent a critical challenge in the manufacturing of monoclonal antibody therapeutics due to their potential to persist during downstream processing. While their enzymatic activity has been characterized, the role of direct HCP‐mAb interactions, particularly those involving polysorbate degrading HCPs, remains poorly understood. In this study, we systematically investigated the binding behavior of four representative polysorbate‐degrading HCPs (CES1F, LPLA2, PAF‐AH, and PPT1) to a panel of mAbs using biolayer interferometry (BLI). All tested HCPs showed specific, transient interactions characterized by fast‐on/fast‐off kinetics, with apparent equilibrium dissociation constants ( K D ) in the low nanomolar range (40–90 nM for strong binders) and rapid dissociation kinetics ( k d > 0.01 s −1 ). This indicates a binding mode characterized by relatively high affinity but limited kinetic stability. Due to incomplete saturation and partially not meeting the quality criteria for kinetic fitting, we complemented model‐based analysis with equilibrium‐derived descriptors. The initial slope of the binding isotherm correlated well with kinetic parameters and enabled robust ranking of interaction strength. To assess hitchhiking relevance during downstream processing, we performed a Protein A chromatography experiment using PLBL2 as a model HCP and two mAbs with different interaction profiles. PLBL2 levels in Protein A elution pools correlated well with interaction propensity confirming that transient interactions can contribute to HCP co‐elution. Our results provide the first systematic and quantitative comparison of polysorbate hydrolase–antibody interactions. They also demonstrate that direct mAb–HCP interaction is a relevant mechanism contributing to HCP persistence during downstream processing.