Trends in clinical development of monoclonal antibodies indicates that there is a nascent shift toward the study of antibody fragments and it is likely that antibody fragments are going to be the next important class of protein-based therapeutics after monoclonal antibodies. Antibody fragments [fragments], in particular the scFvs, Fabs and VHH/VH retain full antigen-binding capacity and superior properties for research, diagnostic and therapeutic applications. Fragments are particularly useful in applications where epitope binding is sufficient for the desired effect including therapeutic applications such as virus neutralization or receptor blocking.
The smallest antigen binding fragment that retains its complete antigen binding site is the Fv fragment, which consists entirely of variable (V) regions. A soluble and flexible amino acid peptide linker is used to connect the V regions to a scFv (single chain fragment variable) fragment for stabilization of the molecule, or the constant (C) domains are added to the V regions to generate a Fab fragment [fragment, antigen-binding]. scFv and Fab are widely used fragments that can be easily produced in prokaryotic hosts. Other Ab formats include disulfide-bond stabilized scFv (ds-scFv), single chain Fab (scFab), as well as di- and multimeric antibody formats like dia-, tria- and tetra-bodies, or minibodies (miniAbs) that comprise different formats consisting of scFvs linked to oligomerization domains. The smallest fragments are VHH/VH of camelid heavy chain Abs and single domain Abs (sdAb). For most therapeutic applications, however, the Fc portion of an Ig is essential as it is instrumental in mediating cytotoxic effector functions such as ADCC and CDC.
Figure 1: The modular domain architecture of Igs has been exploited to create a growing range of alternative antibody formats that spans a molecular-weight range of at least 12–150 kDa and a valency (n) range from monomeric (n = 1), dimeric (n = 2) and trimeric (n = 3) to tetrameric (n = 4) and potentially higher1. The building block that is most frequently used to create novel antibody formats is the single-chain variable (V)-domain antibody fragment (scFv), which comprises V domains from the heavy and light chain (VH and VL domain) joined by a peptide linker of ~15 amino acid residues.
Fab Antibody, scFv, VHH/VH Advantages
- Excellent tissue penetration due to small size2,3
- Better pharmacokinetic properties compared to parent mAbs
- Binding to cryptic epitopes not accessible to full-sized mAbs4
- Absence of cytotoxic effector function5
- Reduced systemic load
- Easy to express and produce in prokaryotic expression system6,7
- Genetically stable
- Less expensive, lowered production costs
- Easy to engineer and modify
The previous section in this series is “Antibody Basics”. To review, click here.
GenScript Antibody Drug Discovery Services
- Antibody Discovery: GenScript's Antibody Engineering group can build antibody library with up to 1010 individual clones, to speed up your antibody discovery efforts.
- Antibody Sequencing: GenScript's advanced Antibody Sequencing technology offers fast and professional sequencing services for your monoclonal antibodies.
- Assays: GenScript has developed several cell-based ADCC/CDC functional assays to profile the efficacy and potency of your therapeutic antibodies using proprietary recombinant effector cells.
- Antibody Engineering: GenScript scientists' extensive experience in antibody engineering can provide superior services such as antibody humanization, affinity maturation and more.
- Antibody Production: With solid expertise in recombinant antibody (rAb) production techniques, GenScript provides a comprehensive rAb service portfolio that deliver microgram to gram quantities of pure rAb for each stage of your Ab drug discovery program.
- PK/PD Study: GenScript offers over 120 tumor and inflammation models for evaluation of in vivo efficacy, PK/PD, biomarker and bioanalysis studies. GenScript Anti-idiotype Antibody services are also a powerful tool for antibody drug PK/PD and immunogenicity studies.
You can also view our Recombinant Antibody Service Selection Guide to identify services that are the best match for your application.
- Carter, P. J. Potent antibody therapeutics by design. Nat Rev Immunol 6, 343-357, doi:10.1038/nri1837 (2006).
- Yokota, T., Milenic, D. E., Whitlow, M. & Schlom, J. Rapid tumor penetration of a single-chain Fv and comparison with other immunoglobulin forms. Cancer Res 52, 3402-3408 (1992).
- Jain, R. K. Physiological barriers to delivery of monoclonal antibodies and other macromolecules in tumors. Cancer Res 50, 814s-819s (1990).
- Ward, E. S., Gussow, D., Griffiths, A. D., Jones, P. T. & Winter, G. Binding activities of a repertoire of single immunoglobulin variable domains secreted from Escherichia coli. Nature 341, 544-546, doi:10.1038/341544a0 (1989).
- Sanz, L., Cuesta, A. M., Compte, M. & Alvarez-Vallina, L. Antibody engineering: facing new challenges in cancer therapy. Acta Pharmacol Sin 26, 641-648, doi:10.1111/j.1745-7254.2005.00135.x (2005).
- Holliger, P. & Hudson, P. J. Engineered antibody fragments and the rise of single domains. Nat Biotechnol 23, 1126-1136, doi:10.1038/nbt1142 (2005).
- Hudson, P. J. & Souriau, C. Engineered antibodies. Nat Med 9, 129-134, doi:10.1038/nm0103-129 (2003).
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