The antibody repertoire of cartilaginous fish comprises an additional heavy-chain-only antibody isotype that is referred to as IgNAR (immunoglobulin novel antigen receptor). Its antigen-binding site consists of one single domain (vNAR) that is reportedly able to engage a respective antigen with affinities similar to those achieved by conventional antibodies. While vNAR domains offer a reduced size, which is often favorable for applications in a therapeutic as well as a biotechnological setup, they also exhibit a high physicochemical stability. Together with their ability to target difficult-to-address antigens such as virus particles or toxins, these shark-derived antibody domains seem to be predestined as tools for biotechnological and diagnostic applications. In the following chapter, we will describe the isolation of anti-idiotypic vNAR domains targeting monoclonal antibody paratopes from semi-synthetic, yeast-displayed libraries. Anti-idiotypic vNAR variants could be employed for the characterization of antibody-based therapeutics (such as antibody-drug conjugates) or as positive controls in immunogenicity assays. Peculiarly, when using semi-synthetic vNAR libraries, we found that it is not necessary to deplete the libraries using unrelated antibody targets, which enables a fast and facile screening procedure that exclusively delivers anti-idiotypic binders.
Keywords: Anti-ID; Anti-idiotypic; Antibody engineering; IgNAR; Protein engineering; Shark; Single-domain antibody; Yeast surface display; vNAR.