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.
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.
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.
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.
Parvalbumin, the major fish allergen, is responsible for IgE cross-reactivity among different fish species. We aimed to generate recombinant single chain antibody fragments (scFv) binding to epitopes responsible for IgE cross-reactivity among parvalbumins.
The parvalbumin-specific scFvs were selected from the human synthetic scFv phage library ETH-2 by alternating the parvalbumin from cod (Gad m 1), carp (Cyp c 1) and trout (Onc m 1) during 3 rounds of sequential biopanning. Based on their reactivity to parvalbumins by ELISA, 2 clones were expressed in Escherichia coli. The ability of the 2 scFv antibodies to inhibit the binding of parvalbumin-specific IgE from fish allergic patients’ sera was showed by ELISA competition experiments and the rat basophilic leukemia mediator release assay.
Based on ability to bind different parvalbumins and sequence analysis, phage clones scFv-gco9 and scFv-goo8 were selected for production of soluble scFv antibodies. We obtained 1 mg of scFv-gco9 and 1.3 mg of scFv-goo8 per litre of bacterial culture. The scFv-gco9 was able to detect all 3 parvalbumins at a concentration of 10 ng/mL. The scFv-goo8 bound to cod parvalbumin, but not to carp and trout parvalbumin. The detection limit for 1 μg/mL of the scFv-gco9 was 0.01 μg/mL of the Gad m 1 and 0.2 μg/mL of Onc m 1 or Cyp c 1. We found that scFv-gco9 dose-dependently blocked the binding of IgE to immobilized Gad m 1, Cyp c 1 and Onc m 1. At a concentration of 5 μg/mL of scFv-gco9 binding of IgE to the 3 parvalbumins was inhibited by approximately 40%, and at a concentration of 20 μg/mL the IgE binding was inhibited to ∼70%. In the case of the scFv-goo8, inhibition of IgE binding to Gad m 1 was about 15%. The inhibition of degranulation of basophils was 55% in the presence of 2 μg/mL scFv-gco9.
This work, supported by grant SFB-F01802, revealed that the scFv antibodies can be used for the standardization of protein extracts used for allergy diagnosis and for IgE epitope mapping. Epitope characterization enables the engineering of parvalbumin molecules with reduced IgE binding for allergen-specific immunotherapy.
In 2009, a novel influenza A/H1N1 virus (H1N1pdm) quickly spread worldwide and co-circulated with then-existing seasonal H1N1 virus (sH1N1). Distinguishing between these 2 viruses was necessary to better characterize the epidemiological properties of the emergent virus, including transmission patterns, pathogenesis, and anti-influenza drug resistance. This situation prompted us to develop a point-of-care virus differentiation system before entering the 2009–2010 influenza season. Aiming to establish H1N1pdm-specific detection tools rapidly, we employed phage display libraries to select H1N1pdm-specific single-chain variable fragments (scFvs).
Human single-fold scFv libraries (Tomlinson I + J) underwent selection for the ability to bind H1N1pdm virus particles. Three rounds of panning brought 1152 phage-bound scFvs, of which 58 clones reacted with H1N1pdm specifically or preferentially over sH1N1 in an enzyme-linked immunosorbent assay (ELISA). After conversion of the scFvs to soluble form, 7 clones demonstrating high/stable expression were finally obtained. However, all the soluble scFvs except No. 29 were found to have lost their specificity/preference for H1N1pdm in ELISA. The specificity/preference of No. 29 was also confirmed by immunofluorescence assay and immunoprecipitation, and the viral nucleoprotein was identified by ELISA as its target protein. The change in specificity associated with scFv conversion from phage-bound to soluble form could be due to loss of phage scaffold pIII protein, which likely provides structural support for the scFv antigen-binding site. It is also possible that the similar antigenic properties of H1N1pdm and sH1N1 led to the observed alterations in scFv specificity.
Using a phage display library, we obtained 7 soluble scFv clones reactive against H1N1pdm; however, only 1 showed specificity/preference toward H1N1pdm. Our results confirmed that using phage display libraries was highly advantageous for the rapid development of molecules to detect target antigens. However, our results also indicated that this strategy might not have been effective for selecting H1N1pdm-specific antibodies during the 2009 pandemic, where the co-circulating sH1N1 virus shared similar antigenic properties. This suggests that it might be advisable to use a synthetic scFv phage display library by strategically considering the characteristics of target antigens and the potential situations.
Influenza; Pandemic; Diagnosis; Single-chain variable fragment (scFv); Altered specificity
There is an ongoing need for standardized, easily renewable immunoreagents for detecting African horsesickness virus (AHSV). Two phage displayed single-chain variable fragment (scFv) antibodies, selected from a semi-synthetic chicken antibody library, were used to develop double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) to detect AHSV. In the DAS-ELISAs, the scFv previously selected with directly immobilized AHSV-3 functioned as a serotype-specific reagent that recognized only AHSV-3. In contrast, the one selected with AHSV-8 captured by IgG against AHSV-3 recognized all nine AHSV serotypes but not the Bryanston strain of equine encephalosis virus. Serving as evidence for its serogroup-specificity. These two scFvs can help to rapidly confirm the presence of AHSV while additional serotype-specific scFvs may simplify AHSV serotyping.
African horsesickness virus; double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA); phage-displayed scFv; serotype-specific
In an effort to further elucidate the early cellular events in generation of antibody responses, we have determined the requirements for antigen-specific initiation of the G0 to G1 transition by isolated trinitrophenol (TNP) -binding B lymphocytes. TNP-binding cells were isolated from normal B6D2F1 splenocyte populations using hapten affinity fractionation on disulfide-bonded TNP-gelatin-coated plates. Populations prepared in this way are greater than or equal to 96% immunoglobulin positive and 70-95% antigen binding. Isolated cells were cultured for 48 h in the presence of a variety of TNP conjugates including TNP-Brucella abortus (Ba), TNP-Ficoll, TNP-sheep erythrocytes (SRBC), TNP-human gamma globulin (HGG), or TNP-ovalbumin (OVA) before being harvested and subjected to acridine orange cell cycle analysis. As many as 80% of cells were in cycle by 48 h in response to TNP-Ba, a thymus-independent (TI1 antigen. A smaller proportion (congruent to 40%) were in cycle in response to TNP-Ficoll, a TI2 antigen. Significant activation was not detected in cultures challenged with the thymus-dependent immunogens TNP-SRBC, TNP-HGG, and TNP-OVA. Addition of interleukin 1 (IL-1), IL-2, B cell growth factor, and/or T cell- replacing factor to cultures did not facilitate responses to these immunogens, suggesting a requirement for antigen-specific T cell help for entry into cell cycle induced by thymus dependent antigens. Activation by TNP-Ba was antigen specific and independent of accessory cells, occurring with equal efficiency in bulk and single-cell cultures. Activation by TNP-Ba was inhibitable by anti-Fab and anti-mu antibodies, but not by anti-delta antibodies. Results indicate that activation of TNP-binding cells to enter cell cycle by TNP-Ba is independent of accessory cells and requires interaction of antigen with cell surface IgM. Exposure to thymus-dependent TNP-immunogens plus nonspecific helper factors is insufficient to cause entry of TNP- binding cells into cycle.
In recent years, there has been a growing focus on use of one-dimensional (1-D) nanostructures, such as carbon nanotubes and nanowires, as transducer elements for label-free chemiresistive/field-effect transistor biosensors as they provide label-free and high sensitivity detection. While research to-date has elucidated the power of carbon nanotubes- and other 1-D nanostructure- based field effect transistors immunosensors for large charged macromolecules such as proteins and viruses, their application to small uncharged or charged molecules has not been demonstrated. In this paper we report a single-walled carbon nanotubes (SWNTs)-based chemiresistive immunosensor for label-free, rapid, sensitive and selective detection of 2,4,6-trinitrotoluene (TNT), a small molecule. The newly developed immunosensor employed a displacement mode/format in which SWNTs network forming conduction channel of the sensor was first modified with trinitrophenyl (TNP), an analog of TNT, and then ligated with the anti-TNP single chain antibody. Upon exposure to TNT or its derivatives the bound antibodies were displaced producing a large change, several folds higher than the noise, in the resistance/conductance of SWNTs giving excellent limit of detection, sensitivity and selectivity. The sensor detected between 0.5 ppb and 5000 ppb TNT with good selectivity to other nitroaromatic explosives and demonstrated good accuracy for monitoring TNT in untreated environmental water matrix. We believe this new displacement format can be easily generalized to other one-dimensional nanostructure-based chemiresistive immuno/affinity-sensors for detecting small and/or uncharged molecules of interest in environmental monitoring and health care.
Carbon nanotubes; chemiresistor; field-effect transistor; label-free; immunosensor; explosives
Phage-display panning is an integral part of biomedical research. Regular panning methods are sometimes complicated by inefficient detachment of the captured phages from the antigen-coated solid supports, which prompted us to modify. Here, we produce an efficient antigen-specific single chain fragment variable (scFv) antibody by using a target-related molecule that favored selection ofrecombinant antibodies.
To produce more selective and specific anti-idiotypic scFv-antibodies from a cDNA library, constructed from HM-1 killer toxin (HM-1)-neutralizing monoclonal antibodies (nmAb-KT), the method was modified by using an elution buffer supplemented with HM-1 that shares structural and functional similarities with the active site of the scFv antibody. Competitive binding of HM-1 to nmAb-KT allowed easy and quick dissociation of scFv-displayed phages from immobilized nmAb-KT to select specific anti-idiotypic scFv antibodies of HM-1. After modified panning, 80% clones (40/50) showed several times higher binding affinity to nmAb-KT than regular panning. The major populations (48%) of these clones (scFv K1) were genotypically same and had strong cytocidal activity against Saccharomyces and Candida species. The scFv K1 (Kd value = 4.62 × 10-8 M) had strong reactivity toward nmAb-KT, like HM-1 (Kd value = 6.74 × 10-9 M) as judged by SPR analysis.
The scFv antibodies generated after modified subtractive panning appear to have superior binding properties and cytocidal activity than regular panning. A simple modification of the elution condition in the phage-display panning protocol makes a large difference in determining success. Our method offers an attractive platform to discover potential therapeutic candidates.
To identify antigens specific for the filamentous form of Candida albicans, a combinatorial phage display library expressing human immunoglobulin heavy and light chain variable regions was used to select phage clones capable of binding to the surfaces of viable C. albicans filaments. Eight distinct phage clones that bound specifically to filament surface antigens not expressed on blastoconidia were identified. Single-chain antibody variable fragments (scFv) derived from two of these phage clones (scFv5 and scFv12) were characterized in detail. Filament-specific antigen expression was detected by an indirect immunofluorescence assay. ScFv5 reacted with C. dubliniensis filaments, while scFv12 did not. Neither scFv reacted with C. glabrata, C. parapsilosis, C. rugosa, C. tropicalis, or Saccharomyces cerevisiae grown under conditions that stimulated filament formation in C. albicans and C. dubliniensis. Epitope detection by the two scFv was sensitive to proteinase K treatment but not to periodate treatment, indicating that the cognate epitopes were composed of protein. The antigens reactive with scFv5 and scFv12 were extractable from the cell surface with Zymolyase, but not with sodium dodecyl sulfate (SDS) and 2-mercaptoethanol, and migrated as polydisperse, high-molecular-weight bands on SDS-polyacrylamide gel electrophoresis gels. The epitopes were detected on clinical specimens obtained from infants with thrush and urinary candidiasis without passage of the organisms on laboratory media, confirming epitope expression in human infection. The availability of a monoclonal immunologic reagent that recognizes filaments from both C. albicans and C. dubliniensis and another specific only to C. albicans adds to the repertoire of potential diagnostic reagents for differentiation between these closely related species.
Recombinant antibody cloning and phage display technologies were used to produce single-chain antibodies (scFv) against Clostridium difficile toxin B. The starting material was the mouse B cell hybridoma line 5A8, which generates a monoclonal antibody against the toxin. The integrated cloning, screening, and phage display system of Krebber et al. (J. Immunol. Methods 201:35-55, 1997) allowed us to rapidly obtain toxin B-binding scFv sequences derived from the hybridoma cell line. The best candidate scFv sequences, based on preliminary enzyme-linked immunosorbent assay (ELISA) screening data were then subcloned into the compatible expression vector. Recombinant single-chain antibodies were expressed in Escherichia coli. A 29-kDa band was observed on polyacrylamide gel electrophoresis as predicted. The expressed product was characterized by immunoblotting and detection with an anti-FLAG antibody. The toxin B-binding function of the single-chain antibody was shown by a sandwich ELISA. The antibody was highly specific for toxin B and did not cross-react with material isolated from a toxin B-negative C. difficile strain. The sensitivity of the soluble single-chain antibody is significantly higher than the original monoclonal antibody based on ELISA data and could detect a minimum of 10 ng of toxin B/well. Competitive ELISAs established that the affinity of the 5A8 parent antibody and the best representative (clone 10) of the single-chain antibodies were similar and in the range of 10−8 M. We propose that recombinant antibody technology is a rapid and effective approach to the development of the next generation of immunodiagnostic reagents.
Antibody repertoires for library construction are conventionally harvested from mRNAs of immune cells. To examine whether germline rearranged immunoglobulin (Ig) variable region genes could be used as source of antibody repertoire, an immunized phage-displayed scFv library was prepared using splenocytic genomic DNA as template. In addition, a novel frame-shifting PCR (fsPCR) step was introduced to rescue stop codon and to enhance diversity of the complementarity-determining region 3 (CDR3). The germline scFv library was initially characterized against the hapten antigen phenyloxazolone (phOx). Sequence analysis of the phOx-selective scFvs indicated that the CDRs consisted of novel as well as conserved motifs. In order to illustrate that the diversity of CDR3 was increased by the fsPCR step, a second scFv library was constructed using a single scFv clone L3G7C as a template. Despite showing similar binding characteristics towards phOx, the scFv clones that were obtained from the L3G7C-derived antibody library gave a lower non-specific binding than that of the parental L3G7C clone. To determine whether germline library represented the endogenous immune status, specific scFv clones for nucleocapsid (N) protein of SARS-associated coronavirus (SCoV) were obtained both from naïve and immunized germline scFv libraries. Both libraries yielded specific anti-N scFvs that exhibited similar binding characteristics towards recombinant N protein, except the immunized library gave a larger number of specific anti-N scFv, and clones with identical nucleotide sequences were found. In conclusion, highly diversified antibody library can be efficiently constructed using germline rearranged immunoglobulin variable genes as source of antibody repertoires and fsPCR to diversify the CDR3.
Staphylococcal food poisoning (SFP) is one of the most prevalent causes of food-borne illness throughout the world. SFP is caused by 21 different types of staphylococcal enterotoxins produced by Staphylococcus aureus. Among these, staphylococcal enterotoxin B (SEB) is the most potent toxin and is a listed biological warfare (BW) agent. Therefore, development of immunological reagents for detection of SEB is of the utmost importance. High-affinity and specific monoclonal antibodies are being used for detection of SEB, but hybridoma clones tend to lose their antibody-secreting ability over time. This problem can be overcome by the use of recombinant antibodies produced in a bacterial system. In the present investigation, genes from a hybridoma clone encoding monoclonal antibody against SEB were immortalized using antibody phage display technology. A murine phage display library containing single-chain variable-fragment (ScFv) antibody genes was constructed in a pCANTAB 5E phagemid vector. Phage particles displaying ScFv were rescued by reinfection of helper phage followed by four rounds of biopanning for selection of SEB binding ScFv antibody fragments by using phage enzyme-linked immunosorbent assay (ELISA). Soluble SEB-ScFv antibodies were characterized from one of the clones showing high affinity for SEB. The anti-SEB ScFv antibody was highly specific, and its affinity constant was 3.16 nM as determined by surface plasmon resonance (SPR). These results demonstrate that the recombinant antibody constructed by immortalizing the antibody genes from a hybridoma clone is useful for immunodetection of SEB.
BACKGROUND: Fibroblast activation protein (FAP) is a type II membrane protein expressed on tumor stroma fibroblasts in more than 90% of all carcinomas. FAP serves as a diagnostic marker and is potential therapeutic target for treatment of a wide variety of FAP+ carcinomas. Murine tumor stroma models and FAP-specific antibodies are required to investigate the functional role of FAP in tumor biology and its usefulness for drug targeting. We here describe the development of antibodies with crossreactivity for human (hFAP) and murine FAP (mFAP), which share 89% amino acid identity. MATERIAL AND METHODS: An FAP-/- mouse was sequentially immunized with recombinant murine and human FAP-CD8 fusion proteins. Immunoglobulin cDNA derived from hyperimmune spleen cells was used for the construction of a combinatorial single chain Fv (scFv) library. Phage display selection of FAP-specific scFv was performed on immobilized hFAP followed by selection on cells expressing murine FAP. RESULTS: High-affinity, species-crossreactive, FAP-specific scFv were isolated upon sequential phage display selection. A bivalent derivative (minibody M036) constructed thereof was applied for immunohistochemical analyses and allowed detection of FAP expression on stroma cells of different human carcinomas as well as on murine host stroma in a tumor xenograft model. CONCLUSIONS: MB M036, derived from phage display selected species crossreactive scFv, is suitable for tumor stroma targeting and will be a valuable tool in the analyses of the functional role of FAP in tumor biology as well as in the evaluation of the suitability of FAP for drug targeting.
Tuberculosis is the leading cause of death due to bacterial infections worldwide, mainly caused by Mycobacterium tuberculosis. The antigen 85 complex comprises a set of major secreted proteins of M. tuberculosis, which are potential biomarkers for diagnostic.
In this work, the first human single chain fragment variable (scFv) antibodies specific for the tuberculosis biomarker 85 B were selected by phage display from naïve antibody gene libraries (HAL7/8). Produced as scFv-Fc in mammalian cells, these antibodies were further characterized and analysed for specificity and applicability in different tuberculosis antigen detection assays. Sandwich detection of recombinant 85 B was successful in enzyme linked immunosorbent assay (ELISA), lateral flow immunoassay and immunoblot. Whereas detection of M. tuberculosis cell extracts and culture filtrates was only possible in direct ELISA and immunoblot assays. It was found that the conformation of 85 B, depending on sample treatment, influenced antigen detection.
Recombinant antibodies, selected by phage display, may be applicable for 85 B detection in various assays. These antibodies are candidates for the development of future point of care tuberculosis diagnostic kits. Using 85 B as a biomarker, the antigen conformation influenced by sample treatment is important.
The filamentous bacteriophage are highly immunogenic particles that can be used as carrier proteins for peptides and presumably other haptens and antigens. Our previous work demonstrated that the antibody response was better focused against a synthetic peptide if it was conjugated to phage as compared to the classical carrier, ovalbumin. We speculated that this was due, in part, to the relatively low surface complexity of the phage. Here, we further investigate the phage as an immunogenic carrier, and the effect reducing its surface complexity has on the antibody response against peptides that are either displayed as recombinant fusions to the phage coat or are chemically conjugated to it. Immunodominant regions of the minor coat protein, pIII, were removed from the phage surface by excising its N1 and N2 domains (Δ3 phage variant), whereas immunodominant epitopes of the major coat protein, pVIII, were altered by reducing the charge of its surface-exposed N-terminal residues (Δ 8 phage variant). Immunization of mice revealed that the Δ3 variant was less immunogenic than wild-type (WT) phage, whereas the Δ8 variant was more immunogenic. The immunogenicity of two different peptides was tested in the context of the WT and Δ3 phage in two different forms: (i) as recombinant peptides fused to pVIII, and (ii) as synthetic peptides conjugated to the phage surface. One peptide (MD10) in its recombinant form produced a stronger anti-peptide antibody response fused to the WT carrier compared to the Δ3 phage carrier, and did not elicit a detectable anti-peptide response in its synthetic form conjugated to either phage carrier. This trend was reversed for a different peptide (4E10L), which did not produce a detectable anti-peptide antibody response as a recombinant fusion; yet, as a chemical conjugate to Δ3 phage, but not WT phage, it elicited a highly focused anti-peptide antibody response that exceeded the anti-carrier response by ~ 65-fold. The results suggest that focusing of the antibody response against synthetic peptides can be improved by decreasing the antigenic complexity of the phage surface.
filamentous phage; vaccine; epitope targeting; peptide
Nitroaromatic compounds are xenobiotics that have found multiple applications in the synthesis of foams, pharmaceuticals, pesticides, and explosives. These compounds are toxic and recalcitrant and are degraded relatively slowly in the environment by microorganisms. 2,4,6-Trinitrotoluene (TNT) is the most widely used nitroaromatic compound. Certain strains of Pseudomonas and fungi can use TNT as a nitrogen source through the removal of nitrogen as nitrite from TNT under aerobic conditions and the further reduction of the released nitrite to ammonium, which is incorporated into carbon skeletons. Phanerochaete chrysosporium and other fungi mineralize TNT under ligninolytic conditions by converting it into reduced TNT intermediates, which are excreted to the external milieu, where they are substrates for ligninolytic enzymes. Most if not all aerobic microorganisms reduce TNT to the corresponding amino derivatives via the formation of nitroso and hydroxylamine intermediates. Condensation of the latter compounds yields highly recalcitrant azoxytetranitrotoluenes. Anaerobic microorganisms can also degrade TNT through different pathways. One pathway, found in Desulfovibrio and Clostridium, involves reduction of TNT to triaminotoluene; subsequent steps are still not known. Some Clostridium species may reduce TNT to hydroxylaminodinitrotoluenes, which are then further metabolized. Another pathway has been described in Pseudomonas sp. strain JLR11 and involves nitrite release and further reduction to ammonium, with almost 85% of the N-TNT incorporated as organic N in the cells. It was recently reported that in this strain TNT can serve as a final electron acceptor in respiratory chains and that the reduction of TNT is coupled to ATP synthesis. In this review we also discuss a number of biotechnological applications of bacteria and fungi, including slurry reactors, composting, and land farming, to remove TNT from polluted soils. These treatments have been designed to achieve mineralization or reduction of TNT and immobilization of its amino derivatives on humic material. These approaches are highly efficient in removing TNT, and increasing amounts of research into the potential usefulness of phytoremediation, rhizophytoremediation, and transgenic plants with bacterial genes for TNT removal are being done.
A single-chain variable fragment (scFv) antibody library against Bordetella pertussis was constructed using M13 phage display. The library was enriched for phages surface displaying functional scFv by biopanning against B. pertussis immobilized on polystyrene plates. Two hundred eighty-eight individual clones from the enriched library were screened for binding to B. pertussis cells, filamentous hemagglutinin (FHA), and pertactin (PRN) in enzyme-linked immunosorbent assays (ELISAs). Based on the binding ability, the clones were put into eight groups. The scFv DNA inserts from the 288 clones were digested with BstOI, and 18 unique restriction patterns, named types 1 to 18, were found. Eight clones (types 1 to 7 and 18) were selected for further testing against FHA, PRN, and B. pertussis by ELISA. The results showed that types 1, 5, 7, and 18 bound strongly to B. pertussis cells as well as FHA and PRN. Type 3 bound strongly to the cells and FHA but weakly to PRN. Types 4 and 6 bound FHA only, and type 2 did not bind to the cells or antigens. The ability of the eight clones to inhibit B. pertussis from binding to HEp-2 cells was assayed. Types 1, 5, and 7, but not the remaining clones, inhibited the adherence of B. pertussis to HEp-2 cells. The scFvs were sequenced, and the deduced amino acid sequence showed that the scFvs were different antibodies. Maltose-binding protein (MBP) fusion proteins composed of three different regions of FHA (heparin-binding domain, carbohydrate recognition domain, and the RGD triplet motif) were constructed. The three fusion proteins and Mal85 (MBP-FHA type I domain) were used to map the binding sites for scFvs of types 1, 5, and 7 by ELISA. The results showed that all three scFvs bound to the heparin-binding domain fusion protein but not the other fusion proteins. BALB/c mice who received recombinant phage-treated B. pertussis had reduced bacterial counts in the nasal cavity, trachea, and lungs compared to the control groups.
The ability of cytosine deaminase (CD) to convert the antifungal agent 5-fluorocytosine (5-FC) into one of the most potent and largely used anticancer compound such as 5-fluorouracil (5-FU) raised considerable interest in this enzyme to model gene or antibody – directed enzyme-prodrug therapy (GDEPT/ADEPT) aiming to improve the therapeutic ratio (benefit versus toxic side-effects) of cancer chemotherapy. The selection and characterization of a human monoclonal antibody in single chain fragment (scFv) format represents a powerful reagent to allow in in vitro and in vivo detection of CD expression in GDEPT/ADEPT studies.
An enzymatic active recombinant CD from yeast (yCD) was expressed in E. coli system and used as antigen for biopanning approach of the large semi-synthetic ETH-2 antibody phage library. Several scFvs were isolated and specificity towards yCD was confirmed by Western blot and ELISA. Further, biochemical and functional investigations demonstrated that the binding of specific scFv with yCD did not interfere with the activity of the enzyme in converting 5-FC into 5-FU.
The construction of libraries of recombinant antibody fragments that are displayed on the surface of filamentous phage, and the selection of phage antibodies against target antigens, have become an important biotechnological tool in generating new monoclonal antibodies for research and clinical applications. The scFvH5 generated by this method is the first human antibody which is able to detect yCD in routinary laboratory techniques without interfering with its enzymatic function.
The heavy-chain and kappa light-chain variable region genes of an antizearalenone hybridoma cell line (2G3-6E3-2E2) were isolated by PCR and joined by a DNA linker encoding peptide (Gly4Ser)3 as a single-chain Fv (scFv) DNA fragment. The scFv DNA fragment was cloned into a phagemid (pCANTAB5E) and expressed as a fusion protein with E tag and phage M13 p3 in Escherichia coli TG1. In the presence of helper phage M13K07, the scFv fusion protein was displayed on the surfaces of recombinant phages. High-affinity scFv phages were enriched through affinity selection in microtiter wells coated with zearalenone-ovalbumin conjugate. The selected recombinant phages were used to infect E. coli HB2151 for the production of soluble scFv antibodies. One selected clone (pQY1.5) in HB2151 secreted a soluble scFv antibody (QY1.5) with a high zearalenone-binding affinity (concentration required for 50% inhibition of binding, 14 ng/ml), similar to that of parent monoclonal antibody in a competitive indirect enzyme-linked immunosorbent assay. However, scFv QY1.5 exhibited higher cross-reactivity with zearalenone analogs and had greater sensitivity to methanol destabilization than the parent monoclonal antibody did. Nucleotide sequence analyses revealed that the light-chain portion of scFv QY1.5 had a nucleotide sequence identity of 97% to a mouse germ line gene VK23.32 in mouse kappa light-chain variable region subgroup V, whereas the heavy-chain nucleotide sequence was classified as mouse heavy-chain subgroup III (D) but without any closely related members having highly homologous complementarity-determining region sequences. The potential of soluble scFv QY1.5 for routine screening of zearalenone and its analogs was demonstrated with zearalenone-spiked corn extracts.
The demand of monospecific high affinity binding reagents, particularly monoclonal antibodies, has been steadily increasing over the last years. Enhanced throughput of antibody generation has been addressed by optimizing in vitro selection using phage display which moved the major bottleneck to the production and purification of recombinant antibodies in an end-user friendly format. Single chain (sc)Fv antibody fragments require additional tags for detection and are not as suitable as immunoglobulins (Ig)G in many immunoassays. In contrast, the bivalent scFv-Fc antibody format shares many properties with IgG and has a very high application compatibility.
In this study transient expression of scFv-Fc antibodies in human embryonic kidney (HEK) 293 cells was optimized. Production levels of 10-20 mg/L scFv-Fc antibody were achieved in adherent HEK293T cells. Employment of HEK293-6E suspension cells expressing a truncated variant of the Epstein Barr virus (EBV) nuclear antigen (EBNA) 1 in combination with production under serum free conditions increased the volumetric yield up to 10-fold to more than 140 mg/L scFv-Fc antibody. After vector optimization and process optimization the yield of an scFv-Fc antibody and a cytotoxic antibody-RNase fusion protein further increased 3-4-fold to more than 450 mg/L. Finally, an entirely new mammalian expression vector was constructed for single step in frame cloning of scFv genes from antibody phage display libraries. Transient expression of more than 20 different scFv-Fc antibodies resulted in volumetric yields of up to 600 mg/L and 400 mg/L in average.
Transient production of recombinant scFv-Fc antibodies in HEK293-6E in combination with optimized vectors and fed batch shake flasks cultivation is efficient and robust, and integrates well into a high-throughput recombinant antibody generation pipeline.
Recombinant Antibodies; Single Chain Fv; scFv-Fc; ImmunoRNase; Transient Mammalian Protein Production; Serum-free medium
We have earlier described a haemagglutination-based assay for on-site detection of antibodies to HIV using whole blood. The reagent in this assay comprises of monovalent Fab fragment of an anti-human RBC antibody fused to immunodominant antigens of HIV-1 and HIV-2. In the present work, we describe a rational and systematic method for directed evolution of scFv and Fab antihuman RBC antibody fragments. Based on homology modeling and germline sequence alignments of antibodies, target residues in the anti-RBC MAb B6 sequence were identified for mutagenesis. A combinatorial library of 107 clones was constructed and subjected to selection on whole RBC under competitive binding conditions to identify several phage-displayed B6 scFv clones with improved binding as determined in an agglutination assay. Selected VL and VH sequences were shuffled to generate a second generation phage-displayed Fab library which on panning yielded Fab clones with several fold better binding than wild type. The mutants with better binding also displayed more Fab molecules per phage particle indicating improved in vivo folding which was also confirmed by their increased periplasmic secretion compared to the wild type. The mutant Fab molecules also showed superior characteristics in large scale production by in vitro folding of LC and Fd. The biophysical measurements involving thermal and chemical denaturation and renaturation kinetics clearly showed that two of the mutant Fab molecules possessed significantly improved characteristics as compared to the wild type B6 Fab. Structural modelling revealed that B6 Fab mutants had increased hydrogen bonding resulting in increased stability. Our approach provides a novel and useful strategy to obtain recombinant antibodies with improved characteristics.
phage display; antibody maturation; Fab; antibody folding; scFv; agglutination
Novel methods are reported for evaluating and utilizing single chain fragment variable (scFv) antibodies derived from yeast-display libraries. Yeast-display was used to select scFv specific to invariant surface glycoproteins (ISG) of Trypanosoma brucei. Alimiting step in the isolation of scFv from non-immune libraries is the conversion of highly active yeast-displayed scFv into soluble antibodies that can be used in standard immunoassays. Challenges include limited solubility or activity following secretion and purification of scFv. For this reason, few scFv derived from yeast-display platforms have moved into development and implementation as diagnostic reagents. To address this problem, assays were developed that employ both yeast-displayed and -secreted scFv as analytical reagents. The first is a competitive inhibition flow cytometry (CIFC) assay that detects secreted scFv by virtue of their ability to competitively inhibit the binding of biotinylated antigen to yeast-displayed scFv. The second is an epitope binning assay that uses secreted scFv to identify additional yeast-displayed scFv that bind non-overlapping or non-competing epitopes on an antigen. The epitope binning assay was used not only to identify sandwich assay pairs with yeast-displayed scFv, but also to identify active soluble scFv present in low concentration in a crude expression extract. Finally, a CIFC assay was developed that bypasses entirely the need for soluble scFv expression, by using yeast-displayed scFv to detect unlabeled antigen in samples. These methods will facilitate the continued development and practical implementation of scFv derived from yeast-display libraries.
Trypanosoma; African trypanosomiasis; antibodies; scFv; yeast-display; S. cerevisiae; invariant surface glycoproteins; ISG; flow cytometry; yeast-display; competitive inhibition
In various clinical studies, Hodgkin’s patients have been treated with anti-CD30 immunotherapeutic agents and have shown promising responses. One of the problems that appeared from these studies is the development of an immune response against the non-human therapeutics, which limits repeated administration and reduces efficacy. We have set out to make a recombinant, human anti-CD30 single-chain variable fragment (scFv) antibody, which may serve as a targeting moiety with reduced immunogenicity and more rapid tumour penetration in similar clinical applications. Rather than selecting a naive phage antibody library on recombinant CD30 antigen, we used guided selection of a murine antibody in combination with panning on the CD30-positive cell line L540. The murine monoclonal antibody Ki-4 was chosen as starting antibody, because it inhibits the shedding of the extracellular part of the CD30 antigen. This makes the antibody better suited for CD30-targeting than most other anti-CD30 antibodies. We have previously isolated the murine Ki-4 scFv by selecting a mini-library of hybridoma-derived phage scFv-antibodies via panning on L540 cells. Here, we report that phage display technology was successfully used to obtain a human Ki-4 scFv version by guided selection. The murine variable heavy (VH) and light (VL) chain genes of the Ki-4 scFv were sequentially replaced by human V gene repertoires, while retaining only the major determinant for epitope-specificity: the heavy-chain complementarity determining region 3 (CDR3) of murine Ki-4. After two rounds of chain shuffling and selection by panning on L540 cells, a fully human anti-CD30 scFv was selected. It competes with the parental monoclonal antibody Ki-4 for binding to CD30, inhibits the shedding of the extracellular part of the CD30 receptor from L540 cells and is thus a promising candidate for the generation of anti-CD30 immunotherapeutics. © 2000 Cancer Research Campaign
CD30; phage display; chain shuffling; human antibody; guided selection
Overexpression of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is commonly occurred in cancers and causes radioresistance and poor prognosis. In present study, the single-chain variable antibody fragments (scFv) targeting DNA-PKcs was developed for the application of radiosensitization in vitro and in vivo. A humanized semisynthetic scFv library and the phage-display antibodies technology were employed to screen DNA-PKcs scFv antibody.
DNA-PKcs epitopes were predicted and cloned. A humanized semisynthetic scFv library and the phage-display antibodies technology were employed to screen DNA-PKcs scFv antibody. DNA damage repair was analyzed by comet assay and immunofluorescence detection of γH2AX foci. The radiosensitization in vivo was determined on Balb/c athymic mice transplanted tumours of HeLa cells.
Four epitopes of DNA-PKcs have been predicted and expressed as the antigens, and a specific human anti-DNA-PKcs scFv antibody gene, anti-DPK3-scFv, was obtained by screening the phage antibody library using the DNA-PKcs peptide DPK3. The specificity of anti-DPK3-scFv was verified, in vitro. Transfection of HeLa cells with the anti-DPK3-scFv gene resulted in an increased sensitivity to IR, decreased repair capability of DNA double-strand breaks (DSB) detected by comet assay and immunofluorescence detection of γH2AX foci. Moreover, the kinase activity of DNA-PKcs was inhibited by anti-DPK3-scFv, which was displayed by the decreased phosphorylation levels of its target Akt/S473 and the autophosphorylation of DNA-PKcs on S2056 induced by radiation. Measurement of the growth and apoptosis rates showed that anti-DPK3-scFv enhanced the sensitivity of tumours transplanted in Balb/c athymic mice to radiation therapy.
The antiproliferation and radiosensitizing effects of anti-DPK3-scFv via targeting DNA-PKcs make it very appealing for the development as a novel biological radiosensitizer for cancer therapeutic potential.
Human papillomaviruses (HPV) are the etiological agents of cervical cancer. The viral E7 protein plays a crucial role in viral oncogenesis. Many strategies have been explored to block the E7 oncoprotein activity. The single-chain variable antibody fragments (scFvs) are valuable tools in cancer immunotherapy and can be used as "intracellular antibodies" to knock out specific protein functions. For both in vivo and in vitro employment, the scFv intrinsic solubility and stability are important to achieve long-lasting effects. Here we report the characterization in terms of reactivity, solubility and thermal stability of three anti-HPV16 E7 scFvs. We have also analysed the scFv43 sequence with the aim of improving stability and then activity of the antibody, previously shown to have antiproliferative activity when expressed in HPV16-positive cells.
The three anti-HPV16 E7 scFv 32, 43 51 were selected from the ETH-2 "phage-display" library. Thermal stability was evaluated with ELISA by determining the residual activity of each purified scFv against the recombinant HPV16 E7, after incubation in the presence of human seroalbumine for different time-intervals at different temperatures. Sequence analysis of the scFvs was performed with BLAST and CLUSTALL programs. The scFv43 aminoacid changes were reverted back to the consensus sequence from the immunoglobuline database by site-directed mutagenesis. ScFv solubility was evaluated with Western blotting by determining their relative amounts in the soluble and insoluble fractions of both prokaryotic and eukaryotic systems.
ScFv51 was the most thermally stable scFv considered. Sequence analysis of the most reactive scFv43 has evidenced 2 amino acid changes possibly involved in molecule stability, in the VH and VL CDR3 regions respectively. By mutagenesis, two novel scFv43-derived scFvs were obtained, scFv43 M1 and M2. ScFv43 M2 showed to have improved thermal stability and solubility in comparison with the parental scFv43.
The characterization of 5 specific anti-HPV16 E7 scFvs shows features important for their activity in vivo. ScFv43 M2 shows higher thermal stability with respect to the parental scFv43, and scFv51 shows high stability and solubility. These properties make the 2 scFvs the best candidates to be tested for anti-E7 activity in vivo.
Murine spleen cells from normal donors were cultured in vitro with trinitrobenzene sulfonate (TNBS)-conjugated soluble proteins, i.e., bovine gamma globulin (TNP-BGG) or bovine serum albumin (TNP-BSA). Addition of 100 μg of any of these TNP-proteins to the spleen cell cultures led to the generation of cytotoxic T-cell effectors which were H-2-restricted and TNP- specific. The lytic potential of such effectors was comparable to that generated by sensitization with TNBS-modified syngeneic cells, and was restricted to haplotypes shared at the K or K plus I-A, or the D regions of the H-2 complex. Greater effecter cell activity was generated by addition of TNP-BGG against TNBS-modified targets which shared K plus I-A than against modified targets which shared the D region with the responding cells, which suggests that the same immune response genes are involved when the response is generated by the addition of TNP-conjugated soluble proteins or of TNBS- modified cells. H-2-restricted, TNP-specific effecter cells were generated by culturing mouse spleen cells with syngeneic cells which had been preincubated with TNP- BGG or TNP-BSA for 1.5 h. The addition of unconjugated soluble proteins to the cultures did not result in cytotoxic effectors detectable on H-2-matched targets, whether the targets were prepared by modification with TNBS, or by incubation with either the unconjugated or TNP-conjugated proteins. Depletion of phagocytic cells in the tumor preparation by Sephadex G-10 column fractionation before incubation with TNP-BSA had no effect on their lysis by the relevant effector cells. Immunofluorescent staining of tumor target cells with anti-TNP antibodies indicated that TNP could be detected on the tumor cells within 10 rain of incubation with TNP-BSA. The cytotoxic response generated by addition of the TNP-proteins to spleen cell cultures was found to be T-cell dependent at the effector phase, as shown by the sensitivity of the lytic phase to absorbed RAMB and complement. Furthermore, the response did not appear to be attributable to antibody-dependent cellular cytotoxicity. Three mechanisms were considered which could account for the generation of H-2-restricted, TNP-specific, cytotoxic T-cell effectors by the addition of soluble TNP-proteins. These include covalent linkage of activated TNP groups from the soluble proteins to cell surface components, macrophage processing of the soluble conjugates and presentation to the responding lymphocytes in association with H-2-coded self structures, or hydrophobic interaction of the TNP-proteins to cell surfaces. Results obtained from sodium dodecyl sulfate gel patterns indicating that cell-bound TNP was still linked to BSA, and the observation that phagocytic-depleted cells could interact with the soluble TNP-proteins and function as H-2-restricted targets, appear not to favor the first two proposed mechanisms.