Non-chromatographic, Ligand-free Platform for Immunoglobulin Purification

Antibodies are extensively used in medicine for therapeutic and diagnostic purposes. They are traditionally purified by 2-3 chromatographic steps, where the first exploits a protein–ligand called Protein A. The latter is used by most, if not all, pharmaceutical companies since it binds to diverse antibody types with high affinity and specificity and leads to high process yields (>90%) and purity (>95%) within a single chromatographic step. However, as the antibody concentration increases, antibody purification becomes challenging, since a single industrial-scale Protein A column cannot capture the entire antibody population. Therefore, we developed an alternative, non-chromatographic antibody purification platform that quantitatively captures antibodies regardless of their concentration. The studied strategy relied on aromatic [metal/chelator] complexes rather than on resins conjugated to Protein A. Two aromatic complexes were evaluated and were composed of a commercially available chelator called bathophenanthroline (batho) bound to either Fe²⁺ or Zn²⁺. Such water-insoluble complexes (i.e., [(batho)₃:Fe²⁺] or [(batho)₃:Zn²⁺]) allow for (a) an efficient separation of IgG antibodies from their mixture with IgM antibodies or (b) the purification of an Fc-fusion protein composed of the Fc-domain of an IgG1 bound to the enzyme acetylcholinesterase. The process yield (>85%, by densitometry) and purity (>95%, by SDS-PAGE) values are encouraging. The recovered targets were monomeric (by dynamic light scattering and Native-PAGE) and preserved their secondary structure (by circular dichroism) and catalytic activity. Purification was achieved at pH~7, thereby circumventing the exposure of antibodies to harsh acidic conditions and, hence, antibody aggregation. The relevance of the developed platform for industrial-scale purification of therapeutic-grade monoclonal antibodies (mAbs) will be further discussed.