INTRODUCTION

Protein A is coupled to a resin support in order to create protein A affinity chromatography media commonly used in the manufacturing of recombinant therapeutic monoclonal antibodies. Natural protein A is derived from Staphylococcus aureus and contains five homologous antibody binding regions and a C-terminal region for cell wall attachment. In addition to naturally derived protein A, recombinant material manufactured in Escherichia coli, as well as several engineered versions of the protein, also manufactured recombinantly, have entered the market place. When immobilized on a column, protein A provides a highly efficient and robust purification method for purifying antibodies at various scales. However, protein A ligand from the column can co-elute with the antibody during purification, an effect which is often referred to as protein A leaching. This tendency increases as the chromatography medium ages. Engineered versions of protein A may improve the pH tolerance of the medium, but do not eliminate leaching. It is the current regulatory expectation that leached protein A should be cleared during the purification of antibodies for human use, and manufacturing processes should be validated accordingly. Enzyme-Linked Immunosorbent Assay (ELISA)-based residuals testing is generally employed during process development and validation to assure the efficient removal of residual protein A during process steps following protein A affinity chromatography. In addition, the manufacturer should have a clear understanding and documentation of resin and ligand quality through raw materials qualification and column lifetime studies.