Study of the conditions for multi‐modal chromatographic capture of Fab′ from dual‐salt precipitated E. coli homogenate

BACKGROUND: In the commercial‐scale purification of immunotherapeutics, Protein A chromatography is employed routinely for its high binding capacity and selectivity. Nevertheless, matrix cost and ligand leaching issues remain and there are many alternatives such as ion‐exchange and multi‐modal resins that are less expensive. However, binding capacities are lower than Protein A owing to the co‐adsorption of protein impurities. One solution involves removing impurities before chromatography by precipitation and a potential approach presented in the literature recently employs a dual‐salt precipitation technique. The current study explores the impact of this upon the capture of an antibody fragment by a multimodal cation exchange resin. RESULTS: The dual salt precipitation procedure employed here removed 36% of the contaminant proteins. A microscale chromatography pipette tip approach was used in a high throughput screening format to scout rapidly for favourable binding conditions successfully. Higher binding capacities were achieved by activating the hydrophobic binding modality of the resin at feed ionic strengths of around 150 mS cm −1 using ammonium sulphate. This was better than using the ion‐exchange modality at below 10 mS cm −1 . CONCLUSIONS: Dual salt precipitation followed by chromatographic capture using this resin were found to be complementary to one another since the removal of protein impurities by dual salt precipitation resulted in a two‐fold improvement in terms of binding capacity. © 2012 Society of Chemical Industry