Ribosome Display Selection of a Murine IgG1 Fab Binding Affibody Molecule Allowing Species Selective Recovery Of Monoclonal Antibodies

Affinity reagents recognizing constant parts of antibody molecules are invaluable tools in immunotechnology applications, including purification, immobilization, and detection of immunoglobulins. In this article, murine IgG₁, the primary isotype of monoclonal antibodies (mAbs) was used as target for selection of novel binders from a combinatorial ribosome display (RD) library of 10¹¹ affibody molecules. Four rounds of selection using three different mouse IgG₁ mAbs as alternating targets resulted in the identification of binders with broad mIgG₁ recognition and dissociation constants (K(D)) in the low nanomolar to low micromolar range. For one of the binders, denoted Z(mab25), competition in binding to full length mIgG₁ by a streptococcal protein G (SPG) fragment and selective affinity capture of mouse IgG₁ Fab fragments after papain cleavage of a full mAb suggest that an epitope functionally overlapping with the SPG-binding site in the CH₁ domain of mouse IgG₁ had been addressed. Interestingly, biosensor-based binding experiments showed that neither human IgG₁ nor bovine Ig, the latter present in fetal bovine serum (FBS) was recognized by Z(mab25). This selective binding profile towards murine IgG₁ was successfully exploited in species selective recovery of two different mouse mAbs from complex samples containing FBS, resembling a hybridoma culture supernatant.