The present inventors discovered that additional aggregation of low-pI antibody can be suppressed by removing formed antibody aggregates after a certain period of time following Protein A column purification, acidic treatment, and neutralization. Furthermore, the present inventors found that efficient impurities removal for a low-pI antibody can be accomplished by using an anion exchange resin in the Bind/Elute mode and then a hydrophobic interaction chromatography or multimodal chromatography resin, compared with conventional methods.
