Improving the binding capacities of protein A chromatographic materials by means of ligand polymerization

• Polymerization of single protein A derived B-domain yields novel affinity ligands.
• Optimization of domain number per ligand improves binding capability.
• High capacity stationary phases were prepared using these ligands.
• Pore accessibility restricts use of prolonged ligands.

Protein A chromatography is one of the most important techniques used in the purification of monoclonal antibodies. Due to the low dynamic binding capacity of protein A chromatographic materials compared to other stationary phases, protein A chromatography is often discussed to be the bottleneck among current purification processes. Several approaches were tested within this study in order to maximize IgG binding capacities of current acrylamido-based based resins. Genetic engineering techniques were used in order to polymerize one of the IgG binding domains (B-domain) of protein A from Staphylococcus aureus (SpA) to achieve ligands with an increased length. The solution-binding ratio and the total size of ligand–antibody complexes were used to characterize the interaction potential of novel ligands, revealing a relatively linear dependency between the number of binding domains upon the amount of bound antibody molecules. This relationship was also valid up to a ligand which was comprised of 8 B-domains after attaching them onto acrylamido-based based stationary phases using epoxy coupling techniques. Equilibrium binding capacities of more than 80 mghIgG mL−1 were achieved using the B8 ligand. Furthermore, static binding capacities, especially for smaller ligands comprised of fewer B-domains, were improved up to 87 mghIgG mL−1 using site-specific coupling chemistry, which is an improvement of more than 20% compared to commercially available materials. In order to evaluate pore exclusion effects due to the use of prolonged affinity ligands, prepared materials were characterized regarding their effective intraparticle porosity and breakthrough capacity.