Host cell protein (HCP) levels in drug products are critical to product quality since HCPs may pose a serious risk to patient safety. The challenge is to accurately quantify the complex mixture of HCP impurities, which vary in properties and abundance depending on the cell line, media, and process parameters. Generic immunoassays commonly used to measure HCP impurities are based on polyclonal antibodies raised against HCPs from non-transfected cell lines. How well a particular HCP assay recognizes all proteins depends…