Dimerization of Fab fragments enables ready screening of phage antibodies that affect hepatocyte growth factor/scatter factor activity on target cells.

A number of applications of antibodies in diagnosis and therapy require multivalent reagents either because of the polymeric nature of the antigens or because biological activity depends on an effect on the formation of homodimeric species. Here, we report a procedure for mass screening of phage-derived monomeric antibody fragments that depend on valency for activity. As a model system, a set of 13 phage-derived human Fab fragments were first selected against mouse and human recombinant hepatocyte growth factor/scatter factor (HGF/SF), a high molecular weight polypeptide growth factor related to the blood protease plasminogen and involved in development and cancer. These Fab fragments were subsequently screened for an effect on HGF/SF activity either as monomeric fragments or after dimerization with a monoclonal antibody (9E10) directed against a peptide tag on the fragments. Fab were identified that either inhibited or enhanced HGF/SF activity on target cell lines, but dimerization was required for this effect. The approach proposed should facilitate mass screening of phage-derived antibody fragments that depend on multiple valency for activity.