How do you assess and ensure production cell line stability?

Cell line stability assessment ensures consistent performance over manufacturing lifespan. Testing approach: extended culture studies (beyond planned production generation), periodic sampling for genotypic and phenotypic characterization, accelerated stability studies at elevated passage numbers. Evaluation criteria: growth characteristics, productivity stability (typically <70% threshold for concern), product quality attributes (glycosylation, charge variants, aggregates), genetic stability (copy number, integration site, sequence integrity), and phenotypic stability. Contributing factors: integration site effects, genetic drift, selective pressure from culture conditions, and metabolic burden. Mitigation strategies: careful clone selection, optimized banking strategy, defined passage limits, monitoring during production. Regulatory expectations: ICH Q5D guidance, stability demonstration to end of in-vitro cell age. Robust cell lines require clonality assurance and comprehensive stability packages.