Protein purification

A process for the purification of an antibody fragment from periplasmic cell extract comprising:

• a) a first chromatography step to capture the antibody fragment by subjecting a mixture comprising the antibody fragment and bacterial host cell protein, wherein bacterial host cell protein is present at 200 μg/ml-10,000 μg/ml and wherein the antibody fragment is at a concentration of at least 1.5 g/L in said mixture, to cation exchange chromatography and subsequent elution, thereby producing a first eluate containing the antibody fragment;
• and
• b) a second chromatography step wherein the first eluate is subjected to anion exchange chromatography to capture impurities and produce a flow through containing the antibody fragment.