Two major mechanisms contributing to copurification of CHO host cell proteins and strategies to minimize their negative impact

For CHO expressed monoclonal antibodies (mAbs), host cell proteins (HCPs) represent a major class of process-related impurities and their removal is a key focus of downstream process development. HCPs are highly heterogeneous in nature, differing in molecular weight, isoelectric point and hydrophobicity, and some of them can be difficult to remove. Although Protein A affinity chromatography alone can typically remove more than 90% of HCPs in the clarified culture harvest, in many cases reducing HCPs in the final drug product to an acceptable level (e.g., <100 ppm) can still be a challenging task. The relative difficulty of HCP clearance is case dependent and in certain cases a small population of HCPs can persist throughout the downstream process. This article reviews the two major mechanisms that contribute to copurification of CHO HCPs, namely leaching from chromatin heteroaggregates and nonspecific HCP-mAb association. In addition, strategies that can minimize the impact of these two factors are briefly discussed.