Identification and characterization of co-purifying CHO host cell proteins in monoclonal antibody purification process

Host cell proteins (HCPs) are process-related impurities derived from the host organism such as Chinese hamster ovary (CHO) cells used for the production of therapeutic mAbs in biopharmaceuticals and potentially pose a risk to patient safety and product efficacy. A number of HCPs have been reported as exceptionally difficult to remove and persist across downstream purification operations into final drug product because they exhibit association with mAbs. Therefore, understanding of HCP impurities and the mAb itself will provide insights into the rational design of efficient downstream process. The aim of this work is to understand mAb interaction with HCPs and identify co-purified HCP subpopulations using two different approaches: (1) Incubation of purified mAb with harvest cell culture fluid (HCCF) from mock-transfected CHO cells (null HCCF) or (2) Immobilization of mAb onto chromatography media followed by incubation with null HCCF. CHO HCP ELISA was used to semi-quantitatively measure the levels of total HCPs. Orthogonal techniques including 2-DE and LC-MS/MS were applied to detect variations in CHO HCP profiles and species. The HCP contents in protein A product pools were significantly higher compared to that in control sample without mAb spiked in and variable HCP levels shown in three different protein A product pools. The majority of HCPs identified by LC-MS/MS in the three protein A product pool showed overlap with the HCP identified in eluate pools from the column immobilized with three different mAbs. The interacting HCPs associated with mAbs were largely involved in catalytic activity. Both approaches demonstrated mAbs bind a common set of HCPs as well as HCPs unique to the mAb.