Thursday, June 18, 2015

Bivalent and Bispecific Single Chain Antibody in Solving the Problems of scFv

Antibody is not a stranger to everyone, even a new born baby. It is the black hole on the biological world, as there is always something new that attracts biologists and researchers.

Since the first success achieved in single chain antibody fragmentscFvresearch by Bird and Huston in the 1988, tremendous achievements have been made in the research and development of single chain antibody technology.

However, in terms of application, there are still problems remain unsettled. The scFv fragments derived from phage display antibody libraries usually have short half-life and less affinity. However, multivalency of antibody molecules turns out to be a desirable property in many in vitro and in vivo applications. After years of experience and great efforts, scientists and researchers from Creative Biolabs have carried out a series of approaches for bivalent and bispecific scFv and Fab construction, which may greatly contribute to the current situation. (Bivalent and Bispecific scFv/Fab)

According to its newest data, there are three approaches of generating genetically engineered and dimerized scFv antibody fragments, miniantibody, diabody and Tandem scFv.

Figure 1. Schematic diagram of bispecific antibody


Bivalent or bispecific (scFv) 2, the so-called miniantibody, is produced by the combination of two scFv molecules with two modified dimerization domains. Leucine zippers are utilized to mediate dimerization of scFv in a miniantibody form. It constructed dimerization cassettes which allow the conversion of scFv antibodies from all its phage display libraries to bivalent or bispecific antibodies. During this procedure, either Fos or Jun leucine zippers are fused to scFv proteins. Two cysteine residues were engineered in the Fos and Jun zipper domains to produce disulfide-stabilized homodimers, which usually leads to efficient production of stable, secreted homodimers that are able to retain their specificity as assessed in a number of assays.


Diabody is a non-covalent dimer of single-chain scFv, fragments that consists of the heavy chain variable (VH) and light chain variable (VL) regions connected by a small peptide linker. 14–15 amino acid residues’ common linkers are long enough to span the distance between the N- termini and C-termini of the variable domains in a scFv. However, utilizing linkers of 3–12 amino acid residues in length can lead to the formation of diabody.

When two ScFvs linked with the short linkers are expressed in the same cells, dual-functional antigen-binding sites will be formed through crossover pairing of the variable light-chains and heavy-chains. The bi-specific diabody, which is constructed with heterogeneous scFvs, is also an important and commonly used form of recombinant bi-specific antibody. A distinct feature of diabody is that it has a rigid structure and can be expressed at high yields in bacteria. See figure 2.
It is worth mentioning here that bispecific T cell engager (BiTE) is a unique form of tandem scFv. In a BiTE molecule, one of the scFvs binds to T cells via CD3 receptor and the other to a tumor cell via a tumor specific molecule. As this procedure brings together the T cell and cancer cell, it has great possibilities in cancer therapy. (BiTE). See figure 2.

Tandem scFv

Tandem scFv (taFv) is produced by connecting two scFv molecules with a short linker. This form of scFv has a very flexible structure and is comparatively easy to be generated. Both bacterial expression and refolding and eukaryotic expression are able to produce tandem scFvs. With years of experiences, Creative Biolabs has successfully constructed over 100 tandem scFvs.

Figure 2. Schematic diagram of Diabody and Tandem scFv

About Creative Biolabs

Creative Biolabs is a professional biotech service provider. Since been established in the year of 2005, it has been focused on the research and development of single chain antibody technology. Learn more about Creative Biolabs.