| Protein A affinity chromatography continues to be the preferred method for commercial purification of antibodies due to its very high selectivity and robust resin performance over repeated purification cycles. It is now estimated that over US$125 billion of yearly sales will be generated from monoclonal antibody (MAb) products by 2020 (1). The clear majority will be purified by large-scale protein A affinity chromatography. With the continued growth and therapeutic commercial importance of MAb production, the availability of high-quality resin material and secondary sourcing are growing concerns. Furthermore, as the current commercial patents for therapeutic antibodies expire, the cost of manufacturing will be of increasing interest.
In bioprocess purification, protein A leakage from chromatography resins must be reduced to acceptable levels before final therapeutic formulation, and it is typically monitored throughout the downstream process. Contaminating host-cell proteins can elicit an undesired immunological response is patients; lot-to-lot variability of these contaminants could potentially cause commercial production of a biotherapeutic to be completely scrapped. Residual DNA contamination can come from either the production host-cell line or microbial contamination. Determination of DNA contamination at each step of a purification process is necessary not only to ensure the removal of host cell DNA, but also to evaluate sterility of that purification process.
In this publication, we evaluate the performance of eight different protein A resins with respect to removal of host-cell proteins (HCP), contaminating residual DNA, and protein A leakage. All resins are marketed for commercial MAb purification and have dynamic binding capacities (DBCs) between 40 g/L and 60 g/L at residence times relevant for batch chromatography (four to six minutes). Whether the objective is to replace an existing in-process purification step or validate two commercial protein A resins for one discrete process, it is imperative that all critical process parameters remain as similar as possible under identical process conditions. The eight resins tested varied with respect to their matrix material, particle size, and type of immobilized protein A. The estimated DBCs (40–60 g/L) are published by the respective vendors. Note that binding capacities of different types of antibodies can differ significantly.
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