Development of an immunoassay for the detection of carbaryl in cereals based on a camelid variable heavy-chain antibody domain

BACKGROUND

The variable domain of camelid heavy-chain antibodies (VHH) is increasingly being adapted to detect small molecules in various matrices. The insecticide carbaryl is widely used in agriculture while its residues have posed a threat to food safety and human health.

RESULTS

VHHs specific for carbaryl were generated from an alpaca immunized with the hapten CBR1 coupled to keyhole limpet hemocyanin. An enzyme-linked immunosorbent assay (ELISA) based on the VHH C1 and the coating antigen CBR2-BSA was developed for the detection of carbaryl in cereals. This assay, using an optimized assay buffer (pH 6.5) containing 10% methanol and 0.8% NaCl, has a half-maximum signal inhibition concentration of 5.4 ng mL^-1 and a limit of detection (LOD) of 0.3 ng mL^-1 for carbaryl, and shows low cross reactivity (≤0.8%) with other tested carbamates. The LOD of carbaryl using the VHH-based ELISA was 36 ng g^-1 in rice and maize and 72 ng g^-1 in wheat. Recoveries of carbaryl in spiked rice, maize and wheat samples were in the range of 81-106%, 96-106% and 83-113%, respectively. Relative standard deviations of repeatability and intra-laboratory reproducibility were in the range of 0.8-9.2% and 2.9-9.7%, respectively.

CONCLUSION

The VHH-based ELISA was highly effective in detecting carbaryl in cereal samples after simple sample extraction and dilution. © 2019 Society of Chemical Industry.

RAGE-specific single chain Fv for PET imaging of pancreatic cancer

Noninvasive detection of both early pancreatic neoplasia and metastases could enhance strategies to improve patient survival in this disease that is notorious for an extremely poor prognosis. There are almost no identifiable targets for non-invasive diagnosis by positron emission tomography (PET) for patients with pancreatic ductal adenocarcinoma (PDAC). Over-expression of the receptor for advanced glycation end products (RAGE) is found on the cell surface of both pre-neoplastic lesions and invasive PDAC. Here, a RAGE-specific single chain (scFv) was developed, specific for PET imaging in syngeneic mouse models of PDAC. An anti-RAGE scFv conjugated with a sulfo-Cy5 fluorescence molecule showed high affinity and selectivity for RAGE expressing pancreatic tumor cells and genetically engineered KRAS^G12D mouse models of PDAC. An in vivo biodistribution study was performed with the ⁶⁴Cu-radiolabled scFv in a syngeneic murine pancreatic cancer model, demonstrating both the feasibility and potential of an anti-RAGE scFv for detection of PDAC. These studies hold great promise for translation into the clinic.

A Combinatory Antibody-Antigen Microarray Assay for High-Content Screening of Single-Chain Fragment Variable Clones from Recombinant Libraries

We have developed a combinatory antibody–antigen microarray for direct screening of multiple single-chain fragment variable (scFv) clones with no need for pre-purification or enrichment before screening. The straightforward workflow allows for early selection of binders to predefined peptide and glycopeptide targets. A capture antibody is contact printed on microarray slides, side by side with the antigens of interest. A large number of scFv clones, in supernatants, are printed on top of the capture antibody and the antigen in a “spot-on-spot” print. The printed scFv clones, which bind to the capture antibody, are detected using biotinylated antigen, while the binding of scFv clones to the printed antigen is detected through a mouse anti-tag antibody. Two different analyses are thus performed on the same slide, generating two kinds of information: one on the ability of an individual scFv clone to bind to the soluble form of the antigen, which may favour selection for higher affinity rather than avidity, while the other allows the identification of large numbers of clones, simultaneously, due to the binding of scFv clones to densely presented antigens, thus providing an overall increased hit rate. The functionality of the new screening approach was illustrated through the generation of antibodies against peptides from the chaperone complex Ku70/Ku80 and the GalNAcα-serine/threonine epitope on the IgA1 alpha chain hinge region. In total, 659 scFv clones were screened with a hit rate of approximately 20%. This approach allowed the identification of functional antibodies in both cases, illustrating the usefulness and capacity of this combinatory microarray screening technique for efficient analysis and validation of antibodies at an early stage of antibody generation.

[Construction of anti-B7-H4-scFv library and screening and identification of anti-B7-H4-scFv]

Objective To construct the ribosome display library of anti-B7-H4 extracellular domain, and select the antibody with high specificity. Methods The cDNA of B7-H4 extracellular domain was amplified from A549 cells by reverse transcription PCR (RT-PCR). To express ectodomains of B7-H4, the sequence of B7-H4 gene, which encodes the B7-H4 extracellular domains, was inserted into plasmid pET-28a(+). The purified recombinant protein of B7-H4 extracellular domain was used to immunize BALB/c mice. The total RNA was extracted from the spleen of BALB/c mice which had been immunized with B7-H4 recombinant protein. The genes of VH, Vκ and VH/Vκ were amplified separately by RT-PCR and splicing by overlap extension PCR (SOE-PCR). The gene of VH/ Vκ was ligated into pUM19-T vector and the ligated sample was transformed into competent E.coli DH5α. The resulting plasmid was isolated and then subjected to sequencing to verify the gene sequence. TNT(R)T7 Quick for PCR DNA kit was used to translate and screen the anti-B7-H4-scFv in vitro from the ribosome display library. Western blotting and an indirect ELISA were performed to detect the specificity of anti-B7-H4-scFv. Results The right sequences of VH, Vκ and VH/Vκ were acquired, which were 439, 680 and 1098 bp in length, respectively. The analysis of specificity demonstrated that the anti-B7-H4-scFv screened from the ribosome display library had a high specific combining ability with B7-H4. Conclusion The experiment has successively constructed the ribosome display library of anti-B7-H4 extracellular domain, and selected the anti-B7-H4-scFv which has a high specific binding ability with recombinant protein of B7-H4 extracelluar domain.

Development of an Immunoassay for Chloramphenicol Based on the Preparation of a Specific Single-Chain Variable Fragment Antibody

Specific antibodies are essential for the immune detection of small molecule contaminants. In the present study, the heavy and light variable regions (V(H )and V(L)) of the immunoglobulin genes from a hybridoma secreting a chloramphenicol (CAP)-specific monoclonal antibody (mAb) were cloned and sequenced. In addition, the light and heavy chains obtained from the monoclonal antibody were separated using SDS-PAGE and analyzed using Orbitrap mass spectrometry. The results of DNA sequencing and mass spectrometry analysis were compared, and the V(H) and V(L) chains specific for CAP were determined and used to construct a single-chain variable fragment (scFv). This fragment was recombinantly expressed as a soluble scFv-alkaline phosphatase fusion protein and used to develop a direct competitive ELISA. Compared with the parent mAb, scFv exhibits lower sensitivity but better food matrix resistance. This work highlights the application of engineered antibodies for CAP detection.

[Selection and identification of completely humanized anti-IL-4 single-chain antibodies]

OBJECTIVE

To express human interleukin 4 (IL-4), select completely humanized anti-IL-4 single-chain antibodies (scFvs) from the completely humanized scFv library and identify their specificity.

METHODS

With IPTG-induced pET102/IL-4/BL21, human IL-4 was synthesized, and then purified and identified. Completely humanized scFvs against IL-4 were expressed from the completely humanized antibody phage library, and positive clones were selected with human IL-4 as antigen. The positive clones were tested by PCR, enzyme cleavage and sequencing. The specificity of the completely humanized anti-IL-4 scFvs was determined by dot blot hybridization.

RESULTS

The relative molecular mass (Mr) of IL-4 fusion protein was about 27 000. With IL-4 as antigen, we obtained the positive clones expressing anti-IL-4 antibodies. PCR showed amplified target bands of about 1000 bp. Enzyme cleavage analysis revealed that fingerprint maps of the selected clones were diverse except 2 clones. Among 4 clones expressing scFvs that had different fingerprint maps and strong binding to IL-4, sequencing showed the sequence of 3 was correct. Then, dot blot hybridization demonstrated that the scFvs expressed by the 3 clones were specific.

CONCLUSION

Completely humanized scFvs against IL-4 has been obtained successfully.

A Novel Dual Expression Platform for High Throughput Functional Screening of Phage Libraries in Product like Format

High throughput screenings of single chain Fv (scFv) antibody phage display libraries are currently done as soluble scFvs produced in E.coli. Due to endotoxin contaminations from bacterial cells these preparations cannot be reliably used in mammalian cell based assays. The monovalent nature and lack of Fc in soluble scFvs prevent functional assays that are dependent on target cross linking and/or Fc functions. A convenient approach is to convert scFvs into scFv.Fc fusion proteins and express them in mammalian cell lines for screening. This approach is low throughput and is only taken after primary screening of monovalent scFvs that are expressed in bacteria. There is no platform at present that combines the benefits of both bacterial and mammalian expression system for screening phage library output. We have, therefore, developed a novel dual expression vector, called pSplice, which can be used to express scFv.Fc fusion proteins both in E.coli and mammalian cell lines. The hallmark of the vector is an engineered intron which houses the bacterial promoter and signal peptide for expression and secretion of scFv.Fc in E.coli. When the vector is transfected into a mammalian cell line, the intron is efficiently spliced out resulting in a functional operon for expression and secretion of the scFv.Fc fusion protein into the culture medium. By applying basic knowledge of mammalian introns and splisosome, we designed this vector to enable screening of phage libraries in a product like format. Like IgG, the scFv.Fc fusion protein is bi-valent for the antigen and possesses Fc effector functions. Expression in E.coli maintains the speed of the bacterial expression platform and is used to triage clones based on binding and other assays that are not sensitive to endotoxin. Triaged clones are then expressed in a mammalian cell line without the need for any additional cloning steps. Conditioned media from the mammalian cell line containing the fusion proteins are then used for different types of cell based assays. Thus this system retains the speed of the current screening system for phage libraries and adds additional functionality to it.

A Strategy for Generating a Broad-Spectrum Monoclonal Antibody and Soluble Single-Chain Variable Fragments against Plant Potyviruses

Potyviruses are major pathogens that often cause mixed infection in calla lilies. To reduce the time and cost of virus indexing, a detection method for the simultaneous targeting of multiple potyviruses was developed by generating a broad-spectrum monoclonal antibody (MAb) for detecting the greatest possible number of potyviruses. The conserved 121-amino-acid core regions of the capsid proteins of Dasheen mosaic potyvirus (DsMV), Konjak mosaic potyvirus (KoMV), and Zantedeschia mild mosaic potyvirus (ZaMMV) were sequentially concatenated and expressed as a recombinant protein for immunization. After hybridoma cell fusion and selection, one stable cell line that secreted a group-specific antibody, named C4 MAb, was selected. In the reaction spectrum test, the C4 MAb detected at least 14 potyviruses by indirect enzyme-linked immunosorbent assay (I-ELISA) and Western blot analysis. Furthermore, the variable regions of the heavy (VH) and light (VL) chains of the C4 MAb were separately cloned and constructed as single-chain variable fragments (scFvs) for expression in Escherichia coli. Moreover, the pectate lyase E (PelE) signal peptide of Erwinia chrysanthemi S3-1 was added to promote the secretion of C4 scFvs into the medium. According to Western blot analysis and I-ELISA, the soluble C4 scFv (VL-VH) fragment showed a binding specificity similar to that of the C4 MAb. Our results demonstrate that a recombinant protein derived from fusion of the conserved regions of viral proteins has the potential to produce a broad-spectrum MAb against a large group of viruses and that the PelE signal peptide can improve the secretion of scFvs in E. coli.

Fluoromodule-based reporter/probes designed for in vivo fluorescence imaging

Optical imaging of whole, living animals has proven to be a powerful tool in multiple areas of preclinical research and has allowed noninvasive monitoring of immune responses, tumor and pathogen growth, and treatment responses in longitudinal studies. However, fluorescence-based studies in animals are challenging because tissue absorbs and autofluoresces strongly in the visible light spectrum. These optical properties drive development and use of fluorescent labels that absorb and emit at longer wavelengths. Here, we present a far-red absorbing fluoromodule-based reporter/probe system and show that this system can be used for imaging in living mice. The probe we developed is a fluorogenic dye called SC1 that is dark in solution but highly fluorescent when bound to its cognate reporter, Mars1. The reporter/probe complex, or fluoromodule, produced peak emission near 730 nm. Mars1 was able to bind a variety of structurally similar probes that differ in color and membrane permeability. We demonstrated that a tool kit of multiple probes can be used to label extracellular and intracellular reporter-tagged receptor pools with 2 colors. Imaging studies may benefit from this far-red excited reporter/probe system, which features tight coupling between probe fluorescence and reporter binding and offers the option of using an expandable family of fluorogenic probes with a single reporter gene.

Development of phage-based single chain Fv antibody reagents for detection of Yersinia pestis

BACKGROUND

Most Yersinia pestis strains are known to express a capsule-like antigen, fraction 1 (F1)(.) F1 is encoded by the caf1 gene located on the large 100-kb pFra plasmid, which is found in Y. pestis but not in closely related species such as Yersinia enterocolytica and Yersinia pseudotuberculosis. In order to find antibodies specifically binding to Y. pestis we screened a large single chain Fv antibody fragment (scFv) phage display library using purified F1 antigen as a selection target. Different forms of the selected antibodies were used to establish assays for recombinant F1 antigen and Y. pestis detection.

METHODS

Phage antibody panning was performed against F1 in an automated fashion using the Kingfisher magnetic bead system. Selected scFvs were screened for F1-binding specificity by one-step alkaline phosphatase enzyme linked immunosorbant assay (ELISA), and assayed for binding to recombinant antigen and/or Y. pestis by flow cytometry and whole-cell ELISA.

RESULTS

Seven of the eight selected scFvs were shown to specifically bind both recombinant F1 and a panel of F1-positive Yersinia cells. The majority of the soluble scFvs were found to be difficult to purify, unstable and prone to cross-reactivity with F1-negative Yersinia strains, whereas phage displayed scFvs were found to be easy to purify/label and remarkably stable. Furthermore direct fluorescent labeling of phage displaying scFv allowed for an easy one-step flow cytometry assay. Slight cross-reactivity was observed when fixed cells were used in ELISA.

CONCLUSIONS

Our high throughput methods of selection and screening allowed for time and cost effective discovery of seven scFvs specifically binding Y. pestis F1 antigen. We describe implementation of different methods for phage-based immunoassay. Based on the success of these methods and the proven stability of phage, we indicate that the use of phage-displayed, rather than phage-free proteins, might generally overcome the shortcomings of scFv antibodies.

Cloning, expression and identification by immunohistochemistry of humanized single-chain variable fragment antibody against hepatitis C virus core protein

Expression of single-chain variable fragment (scFv) antibodies on the surface of bacteriophage is widely used to prepare antibodies with pre-defined specificities. A phage antibody library containing the gene for scFv antibody against Hepatitis C virus core protein was panned with core protein immobilized on microtiter plate wells. After five rounds of panning 60 phage clones specific to core protein were obtained and one selected clone was sequenced. It was found that the specifically detected antigen consists of 774bp and is capable of encoding 257 amino acids in the patients but not in healthy persons.

[Cloning of the variable region genes from hybridoma against HAAH and then construction and expression of anti-HAAH scFv]

AIM

Construction and expression of anti-HAAH single chain variable fragment (scFv) by cloning of the variable region genes from anti-HAAH hybridoma cells G3/F11.

METHODS

Total RNA was extracted from hybridoma cells G3/F11. By RT-PCR, murine V(H) and V(L) genes of mAb were amplified respectively. Then, They were assembled into V(H)-linker-V(L) scFv template by SOE-PCR and anti-HAAH scFv was express in E.coli by constructed pHEN 1-anti-HAAH vector. The expression of anti-HAAH scFv were detected by SDS-PAGE and Western blotting and the binding activity were demonstrated by ELISA.

RESULTS

The analysis of DNA sequencing shown that the full-length of constructed scFv gene was 744 bp, encoding 248 amino acids. Moreover, the V(H) and V(L) genes were functional antibody variable region genes, as there were four FRs and three CDRs in both of them. By SDS-PAGE and Western blotting, the expression level of anti-HAAH scFv were detected. The expression level of pHEN 1-anti-HAAH scFv, which was expressed in E.coli HB2151, was 7.8% in total E.coli protein and were existed in soluble protein mainly. By indirect ELISA detection with HAAH protein, the binding activity of soluble anti-HAAH scFv was very well.

CONCLUSION

The murine V(H) and V(L) genes of mAb against HAAH have been cloned successfully and anti-HAAH scFv have been constructed and expressed. Besides, the scFv could be further studied about their biological activity and application, due to their high affinity shown in preliminary detection.

A novel method for in situ detection of hydrolyzable casein fragments in a cheese matrix by antibody phage display technique and CLSM

A novel method to monitor in situ hydrolyzable casein fragments during cheese ripening by using immunofluorescent labeling and confocal laser scanning microscopy (CLSM) was developed. Monoclonal single chain variable fragments of antibody (scFvs) were generated by antibody phage display toward three small synthetic peptides of the alpha(s1)-casein sequence. These peptides traverse enzymatic cleavage sites of casein during cheese ripening. The specificity of the generated anti-peptide antibodies was determined by ELISA and Western blot. Finally, an immunofluorescent labeling protocol was successfully developed for the detection of scFvs binding to different alpha(s1)-casein fragments inside a cheese matrix by CLSM. To our knowledge, this is the first demonstrated immunofluorescent labeling method for in situ analysis of proteolysis phenomena in the cheese matrix. Additionally, this technique offers a high potential to study in situ dynamic spatial changes of target components in complex food systems.

[Cloning and expression of human single-chain Fv antibody against A beta(1-42) peptide involved in Alzheimer disease]

OBJECTIVE

Screening of antibody clones specific for beta amyloid peptide 1-42 from human phage-display single-chain Fv (scFv) antibody library, and to clone the antibody gene and to express it in a bacterial system, with an ultimate intention to obtain human anti-A beta(1-42) antibody for Alzheimer disease (AD) therapy.

METHODS

beta amyloid peptide 142 was bound on the solid surface of 96 wells plate as the antigen for the binding antibody clones from a human phage-display scFv antibody library. After four rounds of biopanning, random, well-separated colonies were identified by ELISA test. The specific positive phage clones were transfected into the host E. coli HB2151 to express soluble scFv antibodies. These antibodies were identified by SDS-PAGE and Western blot and their antigen-binding activities were determined by ELISA. Genes of the positive scFv antibodies were then sequenced.

RESULTS

ELISA test showed that 7 clones could bind A beta(1-42). The soluble scFv antibody from clone A10 was expressed successfully to produce a 33000 protein present mainly in the whole cell extract which was five folds in amount to that of the control as determined by A490 nm. DNA sequencing demonstrated that the gene of the positive antibody was the scFv gene and the deduced amino acids sequence confirmed its typical antibody V domain structure.

CONCLUSIONS

The specific antibody against A beta(1-42) was successfully identified from human phage-display scFv antibody library. The soluble scFv antibody specific to A beta(1-42) was expressed by E. coli HB2151 in a significant quantity. This cloned antibody promises to provide a solid basis for future studies of the pathogenesis and development of therapeutic agents for Alzheimer's disease.

[Expression of single chain fragment variable P1D3 antibody against shrimp white spot syndrome virus in Pichia pastoris]

White spot syndrome virus (WSSV) is a major pathogen in aquaculture penaeid shrimp, which caused catastrophic economic losses in the worldwide. No adequate treatments against WSSV are available. In order to study infection mechanism of WSSV, a phage display scFv cDNA library against WSSV was constructed and a neutralizing antibody of scFv P1D3 was selected in our lab previously. In this study, scFv P1D3 was expressed successfully in yeast. Firstly, the original expression vector of P1D3, M13 phagmid, was used as a template to design primers with restriction sites of SnaB I and EcoR I . Then the gene of P1D3 was amplified by PCR. After digested by SnaB I and EcoR I , the fragment of scFv P1D3 with E-tag was inserted into yeast and E. coli shuttle plasmid pPIC9k. The recombinant plasmid pPIC9k-scFv P1D3-Etag was linearized with Bgl II and then transformed into Pichia pastoris GS115 by electroporation. Positive clones were selected and verified by PCR and DNA sequencing. The scFv PID3 was induced to express in yeast by methanol. The results of ELISA demonstrate that scFv P1D3 expressed in yeast still has high specificity to bind on WSSV and the binding activity is higher than that expressed in E. coli TG1. After several optimizing experiments, the results show that the expression amount of scFv P1D3 can reach to 302 mg/L in yeast culture supernatant. This experiment has offered a new source of antibody for the researches on passive immunology for shrimp.