How do you ensure adequate host cell protein (HCP) clearance?

HCP clearance is critical for product safety as HCPs can cause immunogenicity. Strategy involves: multi-step orthogonal purification (each step clears different HCP subpopulations), Protein A capture (typically achieves 2-3 log reduction), polishing chromatography (IEX, HIC for additional clearance), and filtration steps. HCP measurement uses process-specific ELISA (ideally with antibodies raised against null cell line HCPs). Specifications typically target <100 ppm, with <10 ppm for some products. Challenging HCPs may co-purify due to product interaction or similar properties. Mitigation includes wash optimization, intermediate holds (HCP precipitation), and HCP-specific removal steps. Cell line engineering can knock out problematic HCPs.