TRIABODIES - SINGLE-CHAIN FV FRAGMENTS WITHOUT A LINKER FORM TRIVALENT TRIMERS

A single chain Fv fragment (scFv) of the murine monoclonal antibody 11 -1G10 was constructed by directly joining the C-terminal residue of th e V-H domain to the N-terminal residue of V-L. 11-1G10 is an anti-idio type and competes with the antigen, influenza virus neuraminidase (NA) , for binding to the NC41 antibody. The scFv formed stable trimers wit h three active antigen combining sites for NC41 Fab fragments, We prop ose that trimeric scFvs may be the preferred conformation for directly linked V-H-V-L molecules, which contrasts the formation of scFv dimer s (diabodies) when the V-H and V-L domains are joined by short flexibl e linkers of between 5-10 residues. BIAcore biosensor binding experime nts showed that the trimeric scFv showed an expected increase in bindi ng affinity, due to avidity, compared to the monomeric 15-residue link ed scFv, The increase in avidity of scFv trimers offers advantages for imaging and immunotherapy. (C) 1997 Federation of European Biochemica l Societies.