Although monoclonal antibodies (MAbs) still represent the most common and most lucrative drug class in the biopharmaceutical industry, enthusiasm is growing for other recombinant-protein products. Clinical pipelines and even commercial portfolios are beginning to feature a breadth of nonantibody proteins and fragments as well as variations on the conventional-antibody theme: e.g., single-chain variable fragments (scFvs), fragment antigen-binding (Fab) products, and single-domain antibody fragments (also called nanobodies). By exploring such formats, drug developers hope to continue leveraging the efficacy advantages of…