Single‐chain Fvs

Single‐chain Fvs (sFvs) are recombinant antibody fragments consisting of only the variable light chain (VL) and variable heavy chain (VH) 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 VL domain from one sFv and the VH domain from a second sFv. Modifying linker length or the inclusion of antigen may stabilize the VL/VH 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)