One-step affinity purification of antibodies is a powerful and widely used tool in the biopharmaceutical industry. Although different strategies can be used to purify immunoglobulin isotype G (IgG), the larger antibody isotype IgM has limited options. Human IgM is the largest antibody and primarily exists as a pentamer in the bloodstream (1). IgM molecules exhibit higher avidity than other antibodies do and serve as essential activators for the complement cascade (1–3). Approaches to IgM purification with hydroxyapatite and ion-exchange (IEX)…