Engineered Bacterial Ligand From <i>Streptococcus pneumoniae</i> on Macroporous Resins for Selective Affinity Capture of Secretory IgA

Secretory immunoglobulin A (sIgA) is a promising emerging biopharmaceutical candidate, but it currently lacks a standardized platform for purification. To address this, a novel affinity chromatography resin was developed by immobilizing protein variants of the Streptococcus pneumoniae surface protein, SpsA, as an affinity ligand. SpsA targets the secretory component of sIgA, which increases selectivity and minimizes co-purification of product-related impurities. Directed attachment between a single cysteine residue and macroporous epoxy-activated supports was employed as an immobilization strategy. Ligand orientation on the resin surface is of utmost importance, as the initial SpsA variant was unable to bind sIgA after immobilization. The cysteine residue was subsequently relocated from the C-terminus to either the N-terminus or loop region of the ligand, resulting in a functional resin. 177 nmol SpsA/mL resin were immobilized on the agarose-based resin, resulting in an equilibrium binding capacity of 9.1 mg sIgA/mL resin. SpsA resin was able to selectively purify sIgA from cell culture supernatant under dynamic conditions with free secretory component as the only product-related impurity. SpsA-based affinity chromatography may enable a scalable purification process for sIgA through an appropriate resin structure and improved selectivity.