Biologic drugs are subject to unique regulatory and technical requirements because of their origin and expression in genetically engineered host cells, as well as their underlying physicochemical properties and elaborate purification processes. One such requirement is the accurate monitoring and effective removal of process-derived impurities such as host-cell proteins (HCPs) and DNA/RNA, viruses, cell culture media, chromatographic leachates, and so on (1). Of those impurities, HCPs are perhaps the most challenging to accurately monitor. Each expression system’s proteome consists of…