SINGLE-CHAIN FVS

Single-chain Fvs (sFvs) are recombinant antibody fragments consisting of only the variable light chain (V-L) and variable heavy chain (V-H) domains covalently connected to one another by a polypeptide linker. D ue to their small size, sFvs have rapid pharmacokinetics and tumor pen etration in vivo. Single-chain Fvs also show a concentration-dependent tendency to oligomerize. Bivalent sFvs are formed when the variable d omains of a sFv disassociate from one another and reassociate with the variable domains of a second sFv. Similar rearrangement and reassocia tion of variable domains from different sFvs can result in the formati on of trimers or higher multimeric oligomers. Each Fv in a bivalent or multivalent Fv is composed of the V-L domain from one sFv and the V-H domain from a second sFv. Modifying linker length or the inclusion of antigen may stabilize the V-L/V-H interface against rearrangement suc h that specific multimeric or monomeric forms of sFvs may be isolated. Nuclear magnetic resonance studies have shown that McPC603-derived Fv and sFvs have similar structures, and that the sFv linker is a rapidl y moving, highly flexible peptide with a random coil-like structure. I n X-ray crystallographic investigations of three different sFvs, linke rs have also been found to be disordered. Indirect evidence suggests t hat a monomeric sFv has been crystallized in one case, and dimeric sFv s in the other two.