Expression of an antibody Fv fragment in myeloma cells

The antigen binding site on antibodies is fashioned by loops at the tips of the β-sheet framework of both heavy and light chain variable domains. A heterodimer of both variable domains (Fv fragment), incorporating loops from an anti-lysozyme antibody, was expressed and secreted from myeloma cells in good yield (8 mg/1 in supernatant from roller bottles), and shown to bind lysozyme. The two subunits were found to be in dynamic equilibrium but are overwhelmingly associated at neutral pH. The small size of Fv fragments (25 × 10 3 M r) make them attractive for structural studies, in vivo imaging, and therapy.