Clusterin: A high-risk host cell protein (HCP) found in CHO-produced drugs
Clusterin is a multifunctional glycoprotein widely expressed in mammalian tissues. It is involved in various physiological processes, including lipid transport, tissue remodeling, and the regulation of apoptosis, and acts as an extracellular molecular chaperone in vivo, stabilizing misfolded or aggregated proteins.
Its function is critical in protecting cells from proteotoxic and oxidative stresses, which cause upregulation of clusterin expression. Clusterin is also active in the regulation of immune responses.
Co-purification with biologics
In 1992, clusterin became the subject of the earliest publication identifying a specific protein binding to IgG. Clusterin has a particularly high affinity for immunoglobulins, binding multivalently to both the Fc and Fab regions of antibodies.
As an HCP, clusterin is highly adhesive and interacts with a wide range of biomolecules, including misfolded proteins, lipids, and cellular debris. Its strong affinity for hydrophobic and aggregated proteins increases the likelihood of clusterin co-purifying with therapeutic proteins during downstream processing and challenges its removal from drug formulations, particularly mAbs.
Clusterin has been found in Protein A-purified mAb products and co-elutes readily with mAbs through CEX and MMC polishing steps.
Immunogenicity concerns
Furthermore, clusterin's immunomodulatory properties exacerbate its risk as an HCP. Clusterin is highly immunogenic and can elicit adverse responses in patients, compromising drug tolerability and safety.
Monitoring clusterin in drug products
Most biopharmaceutical developers rely on ELISA kits for HCP quantification. While useful for overall surveillance, ELISA:
- Does not identify individual HCPs
- Relies on polyclonal antibody recognition, which varies by kit and by animal
- May miss low-abundance or structurally unique HCPs like flagellin or PLBL2
- Cannot differentiate high-risk HCPs from benign ones
As a result, a drug substance may appear “clean” by ELISA standards while still containing HCPs that compromise safety or stability.
LC-MS supports a data-driven approach to process development and quality control, ensuring that manufacturing processes remain predictable, reproducible, and compliant with evolving regulatory expectations. As health authorities increasingly emphasize detailed HCP characterization, LC-MS provides the analytical power to demonstrate robust process control, effective purification, and product stability.
