Protein aggregation kinetics during Protein A chromatography. Case study for an Fc fusion protein.

Protein A chromatography has come to be widely adopted for large-scale purification of monoclonal antibodies and Fc fusion proteins. The low pH conditions required for Protein A elution can often lead to aggregation issues for these products. A concerted study of the kinetics of aggregate formation and their relation to chromatography on Protein A media has been lacking. This paper provides a framework to describe aggregation kinetics for an Fc fusion protein that was highly susceptible to aggregate formation under low pH conditions. In contrast to what is usually expected to be a higher order reaction, first order aggregation kinetics were observed for this protein over a wide range of conditions. A comparison of the rate constants of aggregation forms an effective means of comparing various stabilizing additives to the elution buffer with one another. Inclusion of urea in the elution buffer at moderate concentrations (<2M) and low temperature operation of the Protein A column were both found to be effective solutions to the aggregation issue. Elution from the Protein A resin was found to increase the aggregation rate constants over and above what would be expected from exposure to low pH conditions in solution alone. This demonstrates that Protein A-Fc interactions can destabilize product structure and increase the tendency to aggregate. The results presented here are anticipated to assist the development of Protein A process conditions for products that are prone to form high molecular weight aggregates during column elution.