Antibody fragments are potent active drug substances (1–4). Because they lack glycosylation, they can be produced using different biological expression systems, including yeast and microbial systems as well as mammalian cells. These molecules are interesting as biopharmaceuticals because they are smaller than full-size antibodies and therefore may penetrate better into different tissues. Antibody fragments are cleared faster in biological systems because they lack the Fc antibody structural region (4). However, fragments may be conjugated to increase their size for improved…