Overcoming the Limitations of Protein A: Evolution of Bacterial Protein-Based and Synthetic Affinity Ligands for High-Performance IgG Purification.

Monoclonal antibodies (mAbs) are widely used as therapeutic molecules for the treatment of serious diseases, primarily cancer. The market for mAbs is one of the fastest-growing segments of the biopharmaceuticals industry. Purification is a crucial stage in the production of mAbs. While staphylococcal protein A (SpA) affinity chromatography remains the gold standard in industrial mAb purification, its limitations-low alkaline stability and insufficient binding capacity of SpA, as well as the need for harsh acidic elution conditions-have driven extensive efforts for novel progressive affinity ligands. This review focuses on the development and performance of bacterial protein-based affinity resins for the purification of class G immunoglobulins (IgGs), including conventional proteins A and G, the promising protein L, and the more recently discovered protein M (from M. genitalium), each offering unique specificities for different antibody fragments and species. Hybrid ligands combining domains from multiple bacterial proteins are also discussed, along with next-generation synthetic alternatives such as affibodies, affimers, nanobodies, etc., as well as peptide-based or mixed-mode ligands. The key finding is that the reliable and time-tested resins like those based on protein A continue to dominate the market, although future trends also point toward smaller, more stable, and cost-effective synthetic ligands for specific applications.