Synthesis of ligand-specific phage-display ScFv against the herbicide picloram by direct cloning from hyperimmunized mouse

Nanobody Mediated Atrazine Resistance in Plants

In planta expression of recombinant antibodies has been proposed as a strategy for herbicide resistance but is not well advanced yet. Here, an atrazine nanobody gene fused with a green fluorescent protein tag was transformed to Arabidopsis thaliana, which was confirmed with PCR, ELISA, and immunoblotting. High levels of nanobody accumulation were observed in the nucleus, cytoderm, and cytosol. The nanobody expressed in the plant had similar affinity, sensitivity, and selectivity as that expressed in Escherichia coli. The T3 homozygous line showed resistance in a dose-dependent manner up to 380 g ai/ha of atrazine, which is approximately one-third of the recommended field application rate. This is the first report of utilizing a nanobody in plants against herbicides. The results suggest that utilizing a high-affinity herbicide nanobody gene rather than increasing the expression of nanobodies in plants may be a technically viable approach to acquire commercial herbicide-resistant crops and could be a useful tool to study plant physiology.

Development of an Indirect Competitive Enzyme-Linked Immunosorbent Assay for Glycocholic Acid Based on Chicken Single-Chain Variable Fragment Antibodies

Glycocholic acid (GCA) is an important metabolite of bile acids, whose urine levels are expected to be a specific diagnostic biomarker for hepatocellular carcinoma (HCC). A high-throughput immunoassay for determination of GCA would be of significant advantage and useful for primary diagnosis, surveillance, and early detection of HCC. Single-chain variable fragment (scFv) antibodies have several desirable characteristics and are an attractive alternative to traditional antibodies for the immunoassay. Because chicken antibodies possess single heavy and light variable functional domains, they are an ideal framework for simplified generation of recombinant antibodies for GCA detection. However, chicken scFvs have rarely been used to detect GCA. In this study, a scFv library was generated from chickens immunized with a GCA hapten coupled to bovine serum albumin (BSA), and anti-GCA scFvs were isolated by a phage-displayed method. Compared to the homologous coating antigen, use of a heterologous coating antigen resulted in about an 85-fold improvement in sensitivity of the immunoassay. This assay, under optimized conditions, had a linear range of 0.02-0.18 μg/mL, with an IC50 of 0.06 μg/mL. The assay showed negligible cross-reactivity with various related bile acids, except for taurocholic acid. The detection of GCA from spiked human urine samples ranged from 86.7% to 123.3%. These results, combined with the advantages of scFv antibodies, indicated that a chicken scFv-based enzyme-linked immunosorbent assay is a suitable method for high-throughput screening of GCA in human urine.

Development of anti-CD47 single-chain variable fragment targeted magnetic nanoparticles for treatment of human bladder cancer

Aim: To develop a novel anti-CD47 single-chain variable fragment (scFv) functionalized magnetic nanoparticles (MNPs) for targeting bladder cell lines and its applicability in thermotherapy. Material & methods: An immunized murine antibody phage display library was constructed and screened to isolate anti-CD47 binders. A scFv was selected and conjugated to MNPs which was then utilized to discriminate CD47+ bladder cells along with assessing its efficacy in thermotherapy. Results: An scFv with high affinity to bladder cells was efficiently conjugated to MNPs. Following a hyperthermia treatment, the function of scFv–MNP conjugates led to a considerable reduction in cell viability. Conclusion: The anti-CD47 scFv–MNP conjugate was an effective cancer cell thermotherapy tool that might pave the way for development of bionano-based targeting techniques in both early detection and treatment of cancer.

Rapid isolation of single-chain antibodies from a human synthetic phage display library for detection of Bacillus thuringiensis (Bt) Cry1B toxin

Single chain variable fragment antibody (scFv) is capable of binding its target antigens and is one of the most popular recombinant antibodies format for many applications. In this study, a large human synthetic phage displayed library (Tomlinson J) was employed to generate scFvs against Cry1B toxin by affinity panning. After four rounds of panning, six monoclonal phage particles capable of binding with the Cry1B were isolated, sequenced and characterized by Enzyme-Linked Immunosorbent Assay (ELISA). Two of the identified novel anti-Cry1B scFvs, namely H9 and B12, were expressed in Escherichia coli HB2151 and purified by Ni metal ion affinity chromatography. Sodium dodecyl sulfate polyacrylamine gel electrophoresis (SDS-PAGE) indicated that the relative molecular mass of scFv was estimated at 30 kDa. The purified scFv-H9 was used to develop an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) for Cry1B toxin. The linear range of detection for standards in this ic-ELISA was approximately 0.19-1.1 μg mL⁻¹ and 50% inhibition of control (IC₅₀) was 0.84 μg mL⁻¹ for Cry1B. The affinity of scfv-H9 was (1.95±0.12) × 10⁷ M⁻¹ and showed cross-reactivity with Cry1Ab toxin and Cry1Ac toxin (8.53% and 7.58%, respectively), higher cross-reactivity (12.8%) with Cry1C toxin. The average recoveries of Cry1B toxin from spiked leaf and rice samples were in the range 89.5-96.4%, and 88.5-95.6%, respectively, with a coefficient of variation (C.V) less than 6.0%. These results showed promising applications of scfv-H9 for detecting Cry1B toxin in agricultural and environmental samples.

Immunochemical detection of tissue from the central nervous system via myelin proteolipid protein: adaptation for food inspection and development of recombinant bivalent Fab mini-antibodies

Bovine spongiform encephalopathy (BSE) is transmitted by the ingestion of central nervous system (CNS) tissue of infected animals. Food inspection must, therefore, test for the presence of CNS tissue in meat and meat products. A Western blot assay for the specific CNS tissue marker myelin proteolipid protein (PLP) was optimized with considerably reduced analysis time, solvent consumption, and detection limit (0.001% CNS tissue in minced beef). Further, a PLP-specific recombinant bivalent fragment antigen binding mini-antibody (anti-PLP Fab) was obtained from a commercial phage display library. Western blot analysis with the anti-PLP Fab selectively detected CNS tissue in minced beef with a detection limit of 0.025%. Model experiments for meat processing revealed that assay sensitivity decreased with increasing temperature and prolonged heating time. A market survey with 687 sausage samples was performed using PLP-Western blot and enzyme-linked immunosorbent assay (ELISA) for glial fibrillary acidic protein (GFAP). Five samples were tested clearly positive by both assay systems, whereas in an additional six samples, CNS tissue was detected only by GFAP ELISA and in two samples only by PLP-Western blot.

Applications of single-chain variable fragment antibodies in therapeutics and diagnostics

Antibodies (Abs) are some of the most powerful tools in therapy and diagnostics and are currently one of the fastest growing classes of therapeutic molecules. Recombinant antibody (rAb) fragments are becoming popular therapeutic alternatives to full length monoclonal Abs since they are smaller, possess different properties that are advantageous in certain medical applications, can be produced more economically and are easily amendable to genetic manipulation. Single-chain variable fragment (scFv) Abs are one of the most popular rAb format as they have been engineered into larger, multivalent, bi-specific and conjugated forms for many clinical applications. This review will show the tremendous versatility and importance of scFv fragments as they provide the basic antigen binding unit for a multitude of engineered Abs for use as human therapeutics and diagnostics.

Detection of Sclerotinia sclerotiorum using a monomeric and dimeric single-chain fragment variable (scFv) antibody

Sclerotinia sclerotiorum (Lib.) de Bary is a phytopathogenic fungus capable of causing significant yield losses in numerous crops, including canola, in which the fungus causes sclerotinia stem rot. Immunological detection methods to rapidly determine the presence of S. sclerotiorum on plants may provide growers with a viable diagnostic tool to aid with fungicide use decisions. This paper discusses the generation of a monomeric and dimeric single-chain, variable fragment (scFv) antibody with affinity for S. sclerotiorum using phage display technology. The bacterially expressed and purified scFv is shown to bind S. sclerotiorum with some cross-reactivity with the closely related phytopathogen Botrytis cinerea (Pers.:Fr.). The dimeric scFv displayed improved binding to the fungus as compared to the monomer and could detect the presence of mycelia in inoculated canola petals. To the authors' knowledge, this is the first report of a scFv dimer with affinity for S. sclerotiorum that has the potential for use in the development of a new diagnostic test.

Isolation and affinity maturation of hapten-specific antibodies

More and more recombinant antibodies specific for haptens such as drugs of abuse, dyes and pesticides are being isolated from antibody libraries. Thereby isolated antibodies tend to possess lower affinity than their parental, full-size counterparts, and therefore the isolation techniques must be optimized or the antibody genes must be affinity-matured in order to reach high affinities and specificities required for practical applications. Several strategies have been explored to obtain high-affinity recombinant antibodies from antibody libraries: At the selection level, biopanning optimization can be performed through elution with free hapten, analogue pre-incubation and subtractive panning. At the mutagenesis level, techniques such as random mutagenesis, bacterial mutator strains passaging, site-directed mutagenesis, mutational hotspots targeting, parsimonious mutagenesis, antibody shuffling (chain, DNA and staggered extension process) have been used with various degrees of success to affinity mature or modify hapten-specific antibodies. These techniques are reviewed, illustrated and compared.

Generation of high-affinity chicken single-chain Fv antibody fragments for measurement of the Pseudonitzschia pungens toxin domoic acid

Antibody-based assay systems are now accepted by regulatory authorities for detection of the toxins produced by phytoplankton that accumulate in shellfish tissues. However, the generation of suitable antibodies for sensitive assay development remains a major challenge. We have examined the potential of using the chicken immune system to generate high-affinity, high-specificity recombinant antibody fragments against phytotoxins. Following immunization of the chicken with domoic acid-bovine serum albumin, a single-chain antibody variable region (scFv) gene library was generated from single V(H) and V(L) genes isolated from the immune cells in the spleen and bone marrow. scFvs reacting with domoic acid were isolated by phage display and affinity matured by light chain shuffling, resulting in an approximate 10-fold increase in sensitivity. The isolated scFvs were effectively expressed in Escherichia coli and readily purified by affinity chromatography. They were then used to develop a convenient and sensitive indirect competitive enzyme-linked immunosorbent assay for domoic acid, with a 50% effective dose of 156 ng/ml, which could be used reliably with shellfish extracts. This study demonstrates that chickens provide a valuable model system for the simplified, rapid generation of high-affinity recombinant antibody fragments with specificity for small toxin molecules.

Optimizing recombinant antibody function in SPR immunosensing. The influence of antibody structural format and chip surface chemistry on assay sensitivity

BACKGROUND

Recombinant antibody fragments are valuable tools for SPR-based detection of small molecules such as illicit drugs. However, the multiple structural formats of recombinant antibody fragments are largely uncharacterised with respect to their respective performance in SPR sensing. We have expressed a model anti-M3G antibody in both scFv and chimeric Fab formats to examine its sensitivity and binding profiles in a microplate immunoassay format and Biacore. We have further examined the influence of scFv multimerisation, Fab constant region stability and SPR chip surface coating chemistry, on anti-hapten SPR assay development.

RESULTS

Under optimised competition ELISA conditions, the anti-M3G scFv was found to have an IC(50) value of 30 ng/ml, while the most stable Fab construct exhibited an IC(50) value of 2.4 ng/ml. In SPR competition assay on an M3G-OVA-coated SPR chip surface, the two constructs again differed in sensitivity, with IC(50) values of 117 and 19 ng/ml for the scFv and Fab, respectively (the scFv also exhibiting poor linearity of response). However, when the SPR chip surface was directly coated with M3G, both antibody constructs exhibited good linearity of response, similar high sensitivity IC(50) values (scFv 30 ng/ml, Fab 14 ng/ml) and high reproducibility (50 effective regenerations for M3G-OVA, 200 for M3G direct). During SPR assay development it was noticed that scFv and Fab constructs gave differing off-rate profiles. Subsequent HPLC, ELISA and electrophoretic analyses then confirmed that a portion of the scFv population multimerises. Bivalent scFv was found to profoundly affect the dissociation curve for scFv in stringent SPR kinetic analyses, leading to a 40-fold difference in calculated off-rate values (Fab off rate 4.7 x 10(-3)S(-1), scFv off rate 1.03 x 10(-2)S(-1)).

CONCLUSION

The structural format of recombinant antibody fragments and chip functionalisation methodology can both profoundly affect the function of anti-M3G SPR assay, with direct coating and Fab format proving to be optimal. The confirmation of scFv multimerisation and resulting changes in SPR kinetics profile, in comparison with a Fab, further suggest that caution must be taken in the interpretation of SPR sensorgrams, which are commonly used in the 'affinity ranking' of scFv panels in which the extent of dimerisation in each sample is unknown.

Immunomodulation confers herbicide resistance in plants

In order to create a novel mechanism for herbicide resistance in plants, we expressed a single-chain antibody fragment (scFv) in tobacco with specific affinity to the auxinic herbicide picloram. Transgenic tobacco plants and seedlings expressing this scFv against picloram were protected from its effect in a dose-dependent manner. This is the first successful use of an antibody to confer in vivo resistance to a low molecular weight xenobiotic (i.e. < 1000 Da). Our results suggest the possibility for a generic antibody-based approach to create crops resistant to low molecular weight xenobiotics for subsequent use in the bioremediation of contaminated soils, crop protection and as novel selectable markers.

Selection of hapten-specific single-domain antibodies from a non-immunized llama ribosome display library

Picloram-specific variable fragments (V(HH)s) of heavy chain antibodies (HCAbs) were selected from a nai;ve-llama library using ribosome display technology. A cDNA library of V(HH)s was constructed from lymphocytes of a non-immunized llama and engineered to allow in vitro transcription and translation. With no stop codons present on the transcripts, trimeric complexes of ribosomes, mRNAs and nascent peptides were produced for affinity selection, i.e. panning. After three cycles of panning, seven different V(HH)s all belonging to the V(HH) subfamily 1 were isolated. Following another three cycles of selection, only two of the seven V(HH)s persisted. A comparison of these two sequences with known sequences in the literature suggests that point mutations may have been introduced into the DNA pool during PCR amplification steps of library construction, panning and/or cloning. Three separate point mutations causing three independent amino acid changes (nonsynonomous mutations) accumulated in the same sequence and enriched throughout the selection protocol, suggesting that these changes confer binding advantages. Surface plasmon resonance (SPR) analysis was used to determine binding kinetics of the two clones (3-1D2 and 3-1F6) representing the two different sets of isolated complementarity determining region (CDR)3s. Measured K(D)s were 3 and 254 muM, respectively. The results indicate that ribosome display technology can be used to efficiently isolate hapten-specific antibody (Ab) fragments from a nai;ve library and concurrently introduce diversity to the selected pool thereby facilitating molecular evolution. Ribosome display technology can compensate for the limited diversity of a V(HH) nai;ve library and provide an unlimited source of affinity-matured immunoactive reagents in vitro.

Identification of scFv antibody fragments that specifically recognise the heroin metabolite 6-monoacetylmorphine but not morphine

Use of phage display of recombinant antibodies and large repertoire naïve antibody libraries for identifying antibodies of high specificity has been extensively reported. Nevertheless, there have been few reported antibodies to haptens that have originated from naïve antibody libraries with potential use in diagnostics. We have used chain shuffling of lead single-chain fragment variable (scFv) antibodies, isolated from a naïve antibody library, to screen for antibodies that specifically recognise the major metabolite of heroin, 6-monoacetylmorphine (6MAM). The antibodies were identified by screening high-density colonies of Escherichia coli expressing soluble scFv antibody fragments without prior expression on bacteriophage (phage display). The antibodies recognise 6MAM with affinities of 1-3x10(-7) M with no crossreactivity to morphine. These antibodies can potentially be used for developing a rapid immunoassay in drug-testing programs. To our knowledge, this is the first report of an antibody that distinguishes 6MAM from its de-acetylated form, morphine.

Green fluorescent protein-labeled recombinant fluobody for detecting the picloram herbicide

A green fluorescent protein-labeled fluobody was designed to develop a simple immunoassay method for detecting picloram herbicide in an environmental sample. The gfp gene was successfully inserted into the pSJF2 vector harboring the picloram-specific antibody fragment to yield pSJF2GFP. Picloram spiking in an environmental river sample could be indirectly detected by observing the fluorescence intensity value of the gfp-fluobody, exhibiting specific sensitivity to free picloram with an IC50 value of 50 ppb. Using the gfp-fluobody immunoassay avoids the enzyme-substrate reaction for calorimetric detection that is required in an enzyme-linked immunosorbent assay (ELISA).