1. INTRODUCTION AND SCOPE

Protein-based biotherapeutics are produced by numerous prokaryotic and eukaryotic expression systems such as Escherichia coli (E. coli), yeast (Saccharomyces cerevisiae, Pichia pastoris), human (HEK-293, PER.C6), and Chinese hamster ovary (CHO) cell lines. During manufacture, host cell proteins (HCPs) are a significant class of process-related impurities that are coproduced with the desired product protein. Each HCP has unique physicochemical and biochemical properties. HCPs in biopharmaceuticals are considered a critical quality attribute (CQA) due to their potential impact on product quality, safety, and efficacy. Consequently, residual HCP levels are commonly tested during drug substance release and for process characterization to monitor clearance. HCP analysis is also a critical component of biopharmaceutical product comparability studies where the impact on the upstream expression and/or downstream clearance of HCPs is evaluated before and after process changes. The analytical challenges for quantifying all of the thousands of potential HCPs are well known. This chapter introduces a methodology that provides information on the identity as well as the amount of HCP in samples.