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. Due to their small size. sFvs have rapid pharmacokinetics and tumor penetration in vivo. Single-chain Fvs also show a concentration-dependent tendency to oligomerize, Bivalent sFvs are formed when the variable domains of a sFv disassociate from one another and reassociate with the variable domains of a second sFv, Similar rearrangement and reassociation of variable domains from different sFvs can result in the formation 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 such that specific multimene 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 rapidly moving, highly flexible peptide with a random coil-like structure. In X-ray crystallographic investigations of three different sFvs, linkers have also been found to be disordered. Indirect evidence suggests that a monomeric sFv has been crystallized in one case, and dimeric sFvs in the other two.—Raag, R., Whitlow, M. Single-chain Fvs. FASEB J. 9, 73-80 (1995)