Comparison of protein A affinity sorbents.

Protein A is a popular generic ligand for purification of monoclonal and recombinant antibodies. The performance of 15 commercially available protein A media was studied. Equilibrium and dynamic binding capacity for human IgG was determined and the capture of IgG from a crude feed-stock was investigated. For initial screening the dynamic binding capacity was determined at small scale. Media with good performance were further tested with increased column height. Comparing the data from the two different column heights it could be shown that the dynamic capacity strongly depends on the residence time. Agarose based media exhibited higher binding capacity at residence times longer than 3 min whereas polymeric media or media based on porous glass showed a lesser dependence on the flow velocity and the residence time. A quantitative description of this behavior was derived by determination of the adsorption isotherms and fitting the breakthrough profiles with the Thomas solution. Agarose based media exhibited higher maximum equilibrium binding capacities and the dissociation constants derived from adsorption isotherms were smaller. The other media exhibited higher apparent rate constants, indicating a faster mass transfer. This can be explained by the smaller particle diameter of these media and it can be assumed that constant pattern conditions are thereby obtained more quickly. Selectivity was tested by performing antibody purification under standardized conditions. Polyclonal human IgG in cell culture supernatant containing 2.5% fetal calf serum was used as a representative feed-stock. Under the applied conditions several sorbents showed very tight binding of IgG and in some cases most of the sample remained on the sorbent. The study can be useful as a guide for optimization of large-scale purification processes.