Protein A affinity precipitation of human immunoglobulin G

The potential of protein A affinity precipitation as an alternative method for traditional antibody purification techniques was investigated. Recombinant produced protein A from Staphylococcus aureus (SpA) was covalently linked to the pH-responsive copolymer Eudragit^® S-100 and used for purification of human immunoglobulin G (hIgG). The Eudragit-SpA conjugate had a static binding capacity of 93.9±2.8mg hIgG per g conjugate and a dissociation constant of 787±67nM at 7±1°C. The antibody was adsorbed rapidly onto Eudragit-SpA and reached equilibrium within 5min. An excess of hIgG binding sites, provided by the conjugate, as well as adjusted elution conditions resulted in an appropriate hIgG purification performance. In summary, Eudragit-SpA was successfully applied to capture hIgG from a protein mixture with 65% antibody yield in the elution step. Nearly 96% purity and a purification factor of 12.4 were achieved. The Eudragit-SpA conjugate showed a stable ligand density over several cycles, which enabled reusability for repeated precipitation of hIgG. According to this, pH induced affinity precipitation can be seen as a potential alternative for protein A chromatography in antibody purification processes.