Single-chain variable fragment

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Rotating scFv fragment with highlighted complementarity determining regions (CDRs) ScFv-rotation.gif
Rotating scFv fragment with highlighted complementarity determining regions (CDRs)
The two possible structures of a single-chain variable fragment, with the antigen binding sites including the N-termini on the left and the C-termini on the right. The linker peptides are shown as arrows. Single chain variable fragment.svg
The two possible structures of a single-chain variable fragment, with the antigen binding sites including the N-termini on the left and the C-termini on the right. The linker peptides are shown as arrows.

A single-chain variable fragment (scFv) is not actually a fragment of an antibody, but instead is a fusion protein of the variable regions of the heavy (VH) and light chains (VL) of immunoglobulins, connected with a short linker peptide of ten to about 25 amino acids. [1] The linker is usually rich in glycine for flexibility, as well as serine or threonine for solubility, and can either connect the N-terminus of the VH with the C-terminus of the VL, or vice versa. [2] This protein retains the specificity of the original immunoglobulin, despite removal of the constant regions and the introduction of the linker. [3] The image to the right shows how this modification usually leaves the specificity unaltered.

Contents

These molecules were created to facilitate phage display, where it is highly convenient to express the antigen-binding domain as a single peptide. As an alternative, scFv can be created directly from subcloned heavy and light chains derived from a hybridoma. ScFvs have many uses, e.g., flow cytometry, immunohistochemistry, and as antigen-binding domains of artificial T cell receptors (chimeric antigen receptor).

Unlike monoclonal antibodies, which are often produced in mammalian cell cultures, scFvs are more often produced in bacteria cell cultures such as E. coli . [3]

Purification

Single-chain variable fragments lack the constant Fc region found in complete antibody molecules, and, thus, the common binding sites (e.g., protein G) cannot be used to purify antibodies. These fragments can often be purified or immobilized using protein L, since protein L interacts with the variable region of kappa light chains. More commonly, scientists incorporate a six histidine tag on the c-terminus of the scFv molecule and purify them using immobilized metal affinity chromatography (IMAC). Some scFv can also be captured by protein A if they contain a human VH3 domain. [4] [5] [6]

Bivalent and trivalent scFvs

Structure of divalent (top) and trivalent (bottom) scFvs, tandem (left) and di-/trimerisation format (right) Polyvalent single-chain variable fragments.svg
Structure of divalent (top) and trivalent (bottom) scFvs, tandem (left) and di-/trimerisation format (right)

Divalent (or bivalent) single-chain variable fragments (di-scFvs, bi-scFvs) can be engineered by linking two scFvs. This can be done by producing a single peptide chain with two VH and two VL regions, yielding tandem scFvs. [7] [8] Another possibility is the creation of scFvs with linker peptides that are too short for the two variable regions to fold together (about five amino acids), forcing scFvs to dimerize. This type is known as diabodies. [9] Diabodies have been shown to have dissociation constants up to 40-fold lower than corresponding scFvs, meaning that they have a much higher affinity to their target. Consequently, diabody drugs could be dosed much lower than other therapeutic antibodies and are capable of highly specific targeting of tumors in vivo. [10] Still shorter linkers (one or two amino acids) lead to the formation of trimers, so-called triabodies or tribodies. Tetrabodies have also been produced. They exhibit an even higher affinity to their targets than diabodies. [11]

All of these formats can be composed from variable fragments with specificity for two different antigens, in which case they are types of bispecific antibodies. [12] [13] The furthest developed of these are bispecific tandem di-scFvs, known as bi-specific T-cell engagers (BiTE antibody constructs).

Examples

Related Research Articles

<span class="mw-page-title-main">Antigen</span> Molecule triggering an immune response (antibody production) in the host

In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.

<span class="mw-page-title-main">Antibody</span> Protein(s) forming a major part of an organisms immune system

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. Each tip of the "Y" of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize it directly.

<span class="mw-page-title-main">Phage display</span> Biological technique to evolve proteins using bacteriophages

Phage display is a laboratory technique for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. In this technique, a gene encoding a protein of interest is inserted into a phage coat protein gene, causing the phage to "display" the protein on its outside while containing the gene for the protein on its inside, resulting in a connection between genotype and phenotype. These displaying phages can then be screened against other proteins, peptides or DNA sequences, in order to detect interaction between the displayed protein and those other molecules. In this way, large libraries of proteins can be screened and amplified in a process called in vitro selection, which is analogous to natural selection.

<span class="mw-page-title-main">Carcinoembryonic antigen</span> Glycoprotein secreted into the luminal surface of the epithelia in the gastrointestinal tract

Carcinoembryonic antigen (CEA) describes a set of highly-related glycoproteins involved in cell adhesion. CEA is normally produced in gastrointestinal tissue during fetal development, but the production stops before birth. Consequently, CEA is usually present at very low levels in the blood of healthy adults. However, the serum levels are raised in some types of cancer, which means that it can be used as a tumor marker in clinical tests. Serum levels can also be elevated in heavy smokers.

In biology, chimeric antigen receptors (CARs)—also known as chimeric immunoreceptors, chimeric T cell receptors or artificial T cell receptors—are receptor proteins that have been engineered to give T cells the new ability to target a specific antigen. The receptors are chimeric in that they combine both antigen-binding and T cell activating functions into a single receptor.

<span class="mw-page-title-main">T-cell receptor</span> Protein complex on the surface of T cells that recognises antigens

The T-cell receptor (TCR) is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules. The binding between TCR and antigen peptides is of relatively low affinity and is degenerate: that is, many TCRs recognize the same antigen peptide and many antigen peptides are recognized by the same TCR.

<span class="mw-page-title-main">Single-domain antibody</span> Antibody fragment

A single-domain antibody (sdAb), also known as a NANOBODY®, is an antibody fragment consisting of a single monomeric variable antibody domain. Like a whole antibody, it is able to bind selectively to a specific antigen. With a molecular weight of only 12–15 kDa, single-domain antibodies are much smaller than common antibodies which are composed of two heavy protein chains and two light chains, and even smaller than Fab fragments and single-chain variable fragments.

<span class="mw-page-title-main">Monoclonal antibody therapy</span> Form of immunotherapy

Monoclonal antibody therapy is a form of immunotherapy that uses monoclonal antibodies (mAbs) to bind monospecifically to certain cells or proteins. The objective is that this treatment will stimulate the patient's immune system to attack those cells. Alternatively, in radioimmunotherapy a radioactive dose localizes a target cell line, delivering lethal chemical doses. Antibodies have been used to bind to molecules involved in T-cell regulation to remove inhibitory pathways that block T-cell responses. This is known as immune checkpoint therapy.

<span class="mw-page-title-main">Fragment antigen-binding</span>

The fragment antigen-binding region is a region on an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and the light chain. The variable domain contains the paratope, comprising a set of complementarity-determining regions, at the amino terminal end of the monomer. Each arm of the Y thus binds an epitope on the antigen.

<span class="mw-page-title-main">Fragment crystallizable region</span> Tail region of an antibody

The fragment crystallizable region is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. This region allows antibodies to activate the immune system, for example, through binding to Fc receptors. In IgG, IgA and IgD antibody isotypes, the Fc region is composed of two identical protein fragments, derived from the second and third constant domains of the antibody's two heavy chains; IgM and IgE Fc regions contain three heavy chain constant domains in each polypeptide chain. The Fc regions of IgGs bear a highly conserved N-glycosylation site. Glycosylation of the Fc fragment is essential for Fc receptor-mediated activity. The N-glycans attached to this site are predominantly core-fucosylated diantennary structures of the complex type. In addition, small amounts of these N-glycans also bear bisecting GlcNAc and α-2,6 linked sialic acid residues.

<span class="mw-page-title-main">Protein L</span>

Protein L was first isolated from the surface of bacterial species Peptostreptococcus magnus and was found to bind immunoglobulins through L chain interaction, from which the name was suggested. It consists of 719 amino acid residues. The molecular weight of Protein L purified from the cell walls of Peptostreptoccus magnus was first estimated as 95kD by SDS-PAGE in the presence of reducing agent 2-mercaptoethanol, while the molecular weight was determined to 76kD by gel chromotography in the presence of 6 M guanidine HCl. Protein L does not contain any interchain disulfide loops, nor does it consist of disulfide-linked subunits. It is an acidic molecule with a pI of 4.0. Unlike Protein A and Protein G, which bind to the Fc region of immunoglobulins (antibodies), Protein L binds antibodies through light chain interactions. Since no part of the heavy chain is involved in the binding interaction, Protein L binds a wider range of antibody classes than Protein A or G. Protein L binds to representatives of all antibody classes, including IgG, IgM, IgA, IgE and IgD. Single chain variable fragments (scFv) and Fab fragments also bind to Protein L.

Small modular immunopharmaceuticals, or SMIPs for short, are artificial proteins that are intended for use as pharmaceutical drugs. They are largely built from parts of antibodies (immunoglobulins), and like them have a binding site for antigens that could be used for monoclonal antibody therapy. SMIPs have similar biological half-life and, being smaller than antibodies, are reasoned to have better tissue penetration properties. They were invented by Trubion and are now being developed by Emergent BioSolutions, which acquired Trubion in 2010.

A bispecific monoclonal antibody is an artificial protein that can simultaneously bind to two different types of antigen or two different epitopes on the same antigen. Naturally occurring antibodies typically only target one antigen. BsAbs can be manufactured in several structural formats. BsAbs can be designed to recruit and activate immune cells, to interfere with receptor signaling and inactivate signaling ligands, and to force association of protein complexes. BsAbs have been explored for cancer immunotherapy, drug delivery, and Alzeimer's disease.

<span class="mw-page-title-main">Bi-specific T-cell engager</span>

Bi-specific T-cell engagers (BiTEs) are a class of artificial bispecific monoclonal antibodies that are investigated for use as anti-cancer drugs. They direct a host's immune system, more specifically the T cells' cytotoxic activity, against cancer cells. BiTE is a registered trademark of Micromet AG.

A heavy-chain antibody is an antibody which consists only of two heavy chains and lacks the two light chains usually found in antibodies.

Solitomab is an artificial bispecific monoclonal antibody that is being investigated as an anti-cancer drug. It is a fusion protein consisting of two single-chain variable fragments (scFvs) of different antibodies on a single peptide chain of about 55 kilodaltons. One of the scFvs binds to T cells via the CD3 receptor, and the other to EpCAM as a tumor antigen against gastrointestinal, lung, and other cancers.

<span class="mw-page-title-main">ImmTAC</span>

ImmTACs are a class of bispecific biological drug being investigated for the treatment of cancer and viral infections which combines engineered cancer-recognizing TCRs with immune activating complexes. ImmTACs target cancerous or virally infected cells through binding human leukocyte antigen (HLA) presented peptide antigens and redirect the host's cytotoxic T cells to recognise and kill them.

Synthetic antibodies are affinity reagents generated entirely in vitro, thus completely eliminating animals from the production process. Synthetic antibodies include recombinant antibodies, nucleic acid aptamers and non-immunoglobulin protein scaffolds. As a consequence of their in vitro manufacturing method the antigen recognition site of synthetic antibodies can be engineered to any desired target and may extend beyond the typical immune repertoire offered by natural antibodies. Synthetic antibodies are being developed for use in research, diagnostic and therapeutic applications. Synthetic antibodies can be used in all applications where traditional monoclonal or polyclonal antibodies are used and offer many inherent advantages over animal-derived antibodies, including comparatively low production costs, reagent reproducibility and increased affinity, specificity and stability across a range of experimental conditions.

Creative Biolabs, Inc. is a life-science company which produces and supplies biotech products and services for early drug discovery and development, including various phage display libraries such as pre-made libraries, phage display services, antibody sequencing, and antibody humanization. Customers include pharmaceutical companies, academic institutions, government agencies, clinical research organizations and biotechnology companies.

Recombinant antibodies are antibody fragments produced by using recombinant antibody coding genes. They mostly consist of a heavy and light chain of the variable region of immunoglobulin. Recombinant antibodies have many advantages in both medical and research applications, which make them a popular subject of exploration and new production against specific targets. The most commonly used form is the single chain variable fragment (scFv), which has shown the most promising traits exploitable in human medicine and research. In contrast to monoclonal antibodies produced by hybridoma technology, which may lose the capacity to produce the desired antibody over time or the antibody may undergo unwanted changes, which affect its functionality, recombinant antibodies produced in phage display maintain high standard of specificity and low immunogenicity.

References

  1. ↑ Huston, J. S.; Levinson, D.; Mudgett-Hunter, M.; Tai, M. S.; Novotný, J.; Margolies, M. N.; Crea, R. (1988). "Protein engineering of antibody binding sites: recovery of specific activity in an anti-digoxin single-chain Fv analogue produced in Escherichia coli". Proceedings of the National Academy of Sciences of the United States of America. 85 (16): 5879–5883. Bibcode:1988PNAS...85.5879H. doi: 10.1073/pnas.85.16.5879 . PMC   281868 . PMID   3045807.
  2. ↑ Schirrmann, Thomas (8 November 2004). "Tumorspezifisches Targeting der humanen Natürlichen Killerzellinie YT durch Gentransfer chimärer Immunglobulin-T-Zellrezeptoren" (in German). Berlin. doi:10.18452/15246.{{cite journal}}: Cite journal requires |journal= (help)
  3. 1 2 Peterson, Eric; Owens, SM; Henry, RL (2006). "Monoclonal Antibody Form and Function: Manufacturing the Right Antibodies for Treating Drug Abuse". AAPS Journal. 8 (2): E383–E390. doi:10.1208/aapsj080243. PMC   3231570 . PMID   16796389.
  4. 1 2 Vostakolaei, Mehdi Asghari; Molavi, Ommoleila; Hejazi, Mohammad Saeid; Kordi, Shirafkan; Rahmati, Saman; Barzegari, Abolfazl; Abdolalizadeh, Jalal (September 2019). "Isolation and characterization of a novel scFv antibody fragments specific for Hsp70 as a tumor biomarker". Journal of Cellular Biochemistry. 120 (9): 14711–14724. doi:10.1002/jcb.28732. ISSN   0730-2312. PMID   30998271. S2CID   121351794.
  5. ↑ Potter, K. N.; Li, Y.; Pascual, V.; Capra, J. D. (1997). "Staphylococcal protein a binding to VH3 encoded immunoglobulins". International Reviews of Immunology. 14 (4): 291–308. doi:10.3109/08830189709116521. PMID   9186782.
  6. ↑ Kordi, Shirafkan; Rahmati-Yamchi, Mohammad; Asghari Vostakolaei, Mehdi; Barzegari, Abolfazl; Abdolalizadeh, Jalal (2019-02-21). "Purification of a Novel Anti-VEGFR2 Single Chain Antibody Fragmentand Evaluation of Binding Affinity by Surface Plasmon Resonance". Advanced Pharmaceutical Bulletin. 9 (1): 64–69. doi:10.15171/apb.2019.008. ISSN   2228-5881. PMC   6468230 . PMID   31011559.
  7. ↑ Xiong, Cheng-Yi; Natarajan, A; Shi, XB; Denardo, GL; Denardo, SJ (2006). "Development of tumor targeting anti-MUC-1 multimer: effects of di-scFv unpaired cysteine location on PEGylation and tumor binding". Protein Engineering Design and Selection. 19 (8): 359–367. doi: 10.1093/protein/gzl020 . PMID   16760193.
  8. ↑ Kufer, Peter; Lutterbüse, Ralf; Baeuerle, Patrick A. (2004). "A revival of bispecific antibodies" (PDF). Trends in Biotechnology. 22 (5): 238–244. doi:10.1016/j.tibtech.2004.03.006. PMID   15109810.
  9. ↑ Hollinger, Philipp; Prospero, T; Winter, G (July 1993). ""Diabodies": small bivalent and bispecific antibody fragments". Proceedings of the National Academy of Sciences of the United States of America. 90 (14): 6444–8. Bibcode:1993PNAS...90.6444H. doi: 10.1073/pnas.90.14.6444 . PMC   46948 . PMID   8341653.
  10. 1 2 Adams, GP; Schier, R; McCall, AM; Crawford, RS; Wolf, EJ; Weiner, LM; Marks, JD (1998). "Prolonged in vivo tumour retention of a human diabody targeting the extracellular domain of human HER2/neu". British Journal of Cancer. 77 (9): 1405–12. doi:10.1038/bjc.1998.233. PMC   2150193 . PMID   9652755.
  11. ↑ Le Gall, F.; Kipriyanov, SM; Moldenhauer, G; Little, M (1999). "Di-, tri- and tetrameric single chain Fv antibody fragments against human CD19: effect of valency on cell binding". FEBS Letters. 453 (1): 164–168. doi: 10.1016/S0014-5793(99)00713-9 . PMID   10403395. S2CID   20213440.
  12. ↑ Dincq, S; Bosman, F; Buyse, MA; Degrieck, R; Celis, L; De Boer, M; Van Doorsselaere, V; Sablon, E (2001). "Expression and purification of monospecific and bispecific recombinant antibody fragments derived from antibodies that block the CD80/CD86-CD28 costimulatory pathway". Protein Expression and Purification. 22 (1): 11–24. doi:10.1006/prep.2001.1417. PMID   11388794.
  13. ↑ Kellner, C (2008). Entwicklung und Charakterisierung bispezifischer Antikörper-Derivate zur Immuntherapie CD19-positiver Leukämien und Lymphome [Development and characterisation of bispecific antibody derivatives for the immunotherapy of CD19-positive leukaemia and lymphoma] (Thesis) (in German and English). Erlangen-Nürnberg: Friedrich-Alexander-Universität.
  14. ↑ Mathew, JP; Shernan, SK; White, WD; Fitch, JC; Chen, JC; Bell, L; Newman, MF (2004). "Preliminary report of the effects of complement suppression with pexelizumab on neurocognitive decline after coronary artery bypass graft surgery". Stroke: A Journal of Cerebral Circulation. 35 (10): 2335–9. doi: 10.1161/01.STR.0000141938.00524.83 . PMID   15331798.
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