Production and ELISA application of bispecific monoclonal antibodies against fluorescein isothiocyanate (FITC) and horseradish peroxidase (HRP)

Paper-Based Biosensors for the Detection of Nucleic Acids from Pathogens

Paper-based biosensors are microfluidic analytical devices used for the detection of biochemical substances. The unique properties of paper-based biosensors, including low cost, portability, disposability, and ease of use, make them an excellent tool for point-of-care testing. Among all analyte detection methods, nucleic acid-based pathogen detection offers versatility due to the ease of nucleic acid synthesis. In a point-of-care testing context, the combination of nucleic acid detection and a paper-based platform allows for accurate detection. This review offers an overview of contemporary paper-based biosensors for detecting nucleic acids from pathogens. The methods and limitations of implementing an integrated portable paper-based platform are discussed. The review concludes with potential directions for future research in the development of paper-based biosensors.

Synthetic chemical ligands and cognate antibodies for biorthogonal drug targeting and cell engineering

A vast range of biomedical applications relies on the specificity of interactions between an antigen and its cognate receptor or antibody. This specificity can be highest when said antigen is a non-natural (synthetic) molecule introduced into a biological setting as a bio-orthogonal ligand. This review aims to present the development of this methodology from the early discovery of haptens a century ago to the recent clinical trials. We discuss such methodologies as antibody recruitment, artificial internalizing receptors and chemically induced dimerization, present the use of chimeric receptors and/or bispecific antibodies to achieve drug targeting and transcytosis, and illustrate how these platforms most impressively found use in the engineering of therapeutic cells such as the chimeric antigen receptor cells. This review aims to be of interest to a broad scientific audience and to spur the development of synthetic artificial ligands for biomedical applications.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Bispecific antibody-mediated detection of the Staphylococcus aureus thermonuclease

We report a novel fluorescence-based immunoassay which enables qualitative detection of the Staphylococcus aureus Thermonuclease (TNase) enzyme, thus providing confirmation of the presence of the S. aureus bacterium in vitro. The biomedical problem of chronic wound healing and the continuing emergence of antibiotic-resistant species is addressed in the development of a detection system capable of the rapid, real-time assessment of bacterial load and diversity. The use of bispecific antibodies (BsAb) provides integration of the molecular detection and signal response components of a standard immunoassay due to steric hindrance-mediated release of prebound fluorescent reporter molecules upon specific binding of TNase to adjacent sites. Rhodamine and fluorescein-labeled hemocyanin from Megathura crenulata (KLH) were prepared as effective immunoconjugates containing a sensitive fluorescent reporter moiety. BsAb that both specifically quenched the fluorescence of the reporter conjugate and bound the TNase target antigen were produced using cell fusion techniques. Assays were then performed to analyze the properties attributable to the steric hindrance-mediated release of the fluorescent reporter molecules upon adjacent TNase binding. This was performed by monitoring the intensity of fluorescence emission of the immunogenic reporter conjugate released into an aqueous environment at 578 and 520 nm, respectively.

Generation and application of a fluorescein-specific single chain antibody

A recombinant single chain antibody fragment (designated scDE1) of the murine monoclonal anti-fluorescein antibody B13-DE1 was generated using the original hybridoma cells as source for the variable antibody heavy and light chain (VH and VL) genes. After cloning the variable genes into a phage vector a functional antibody fragment was selected by phage display panning. Recombinant antibody could be expressed as phage antibody and as soluble single chain antibody in Escherichia coli. High yield of scDE1 could also be detected in bacterial culture supernatant. The scDE1 showed the same binding specificity as the parental monoclonal antibody, i.e. it bound fluorescein, fluorescein derivatives and a fluorescein peptide mimotope. Surface plasmon resonance revealed a K(D) of 19 nM for the scDE1 compared to 0.7 nM for the monoclonal antibody. The isolated soluble scDE1 could easily be conjugated to horseradish peroxidase which allowed the use of the conjugate as universal indicator for the detection of fluorescein-labelled proteins in different immunoassays. Detection of hCG in urine was performed as a model system using scDE1. In addition to E. coli the scFv genes could also be transferred and expressed in eukaryotic cells. Finally, we generated HEK293 cells expressing the scDE1 at the cell surface.

Use of bispecific antibodies in molecular velcro assays whose specificity approaches the theoretical limit of immunodetection for Bordetella pertussis

A bispecific monoclonal antibody (bsMAb) that detects Bordetella pertussis, the causative agent of whooping cough, and horseradish peroxidase (HRPO) has been developed by use of the quadroma technology. A quadroma, P123, was produced by fusing two well-characterized hybridomas against the bacterium and the enzyme and was subcloned to obtain a stable bsMAb-secreting cell line. The quadroma was theoretically expected to produce up to 10 different molecular species of immunoglobulins, so secreted bispecific antibody was complexed with excess HRPO and the HRPO-bsMAb complex was purified in one step by benzhydroxamic acid-agarose affinity cochromatography. An ultrasensitive homosandwich molecular "velcro" enzyme-linked immunosorbent assay for the detection of B. pertussis whole bacteria with HRPO-bsMAb was established in both microplate and nasopharyngeal swab formats. This assay demonstrates a high sensitivity that approaches the theoretical limit of detection of one bacterium. This new nanoprobe can be used to develop a new generation of assays that are simple, inexpensive alternatives to quantitative PCR and that can be used by clinical laboratories. This strategy of homosandwich assays with solid-phase monospecific antibodies and solution-phase bsMAb with specificity for the same repeating surface determinants can be applied to generate ultrasensitive immunodiagnostic assays for viruses and bacteria.

Bispecific antibody conjugates in therapeutics

Bispecific monoclonal antibodies have drawn considerable attention from the research community due to their unique structure against two different antigens. The two-arm structure of bsMAb allows researchers to place a therapeutic agent on one arm while allowing the other to specifically target the disease site. The therapeutic agent can be a drug, toxin, enzyme, DNA, radionuclide, etc. Furthermore, bsMAb may redirect the cytotoxicity of immune effector cells towards the diseased cells or induce a systemic immune response against the target. BsMAb holds great promise for numerous therapeutic needs in the light of: (1) recent breakthroughs in recombinant DNA technology, (2) the increased number of identified disease targets as the result of the completion of human genomic map project, and (3) a better understanding of the mechanism of human immune system. This review focuses on therapeutic applications and production of bsMAb while providing the up-to-date clinical trial information.

Affinity chromatography and co-chromatography of bispecific monoclonal antibody immunoconjugates

Bispecific monoclonal antibodies (bsMAb) are unique macromolecules functioning as cross-linkers with two different predetermined binding specificities. A wide range of potential applications employing these probes can be envisioned in immunodiagnostics and immunotherapy. One of the major limitations for the use of bsMAbs produced by hybrid-hybridomas is the production of parental monospecific antibodies along with bsMAbs. Hence, the purification of desired bsMAb free from both parental mAbs and other possible promiscuous combinations is essential. Purification of antibodies is the single greatest obstacle in obtaining an immunoprobe with high specific activity. This review describes the affinity purification and affinity co-purification techniques for the separation of bsMAb as a pre-formed immune complex or as a pure species. The use of immobilized ligands is the basis of affinity chromatography. Affinity chromatography can be classified into three different categories depending on the properties of the immobilized ligand. The ligand-specific affinity chromatography is based on the extremely specific immobilized ligand, directed towards the protein or antibody of interest. Using a dual, sequential affinity chromatography, bsMAb can be purified from a mixture of bispecific and monospecific monoclonal antibodies with a ligand specific for each antibody. Thiophilic adsorption is a group-specific affinity method that can be successfully used to separate monospecific forms from bispecific species by salt gradient elution. Affinity co-chromatography offers a convenient one-step method for purification of bulk amounts of immunoconjugates for diagnostic applications by exploiting several dye-ligands known to bind certain enzymes. The same method could be potentially used for quality control and quality assurance purposes in industrial biotechnology.

Affinity purification of novel bispecific antibodies recognising carcinoembryonic antigen and doxorubicin

We have developed a method which combines Protein A affinity chromatography and HPLC analytical and semipreparative hydroxyapatite affinity chromatography to purify bispecific antibodies (BsMabs) from hybrid-hybridomas secreting antibodies recognising carcinoembryonic antigen (CEA) and the chemotherapeutic drug doxorubicin (Dox). Elution of the HPLC hydroxyapatite columns with a 60-360 mM phosphate buffer gradient was found to give better separation than elution with a 60-180 mM phosphate buffer gradient. Careful monitoring of HPLC fractions by enzyme linked immunosorbent assays for anti-CEA, anti-Dox and dual anti-CEA/anti-Dox activity, and pooling of fractions on the basis of these results, enabled the purification of novel BsMabs for use in in vitro and preclinical in vivo experiments.

Bispecific antibodies as novel bioconjugates

Bispecific antibodies are unique macromolecular heterobifunctional cross-linkers with two different binding specificities within a single molecule. As ideal bioconjugates, they can specifically glue any two different molecules together without the need for chemical conjugation. With this unique feature, they have immense potential in biological and immunological fields. Their applications range from immunohistochemistry, immunoassays, radioimmunodiagnosis, radioimmunotherapy, and immunotherapy. Recently, a new second generation of bispecific molecules, bispecific single chain Fv and diabodies, has been produced by DNA recombinant technology. They can be considered as the ultimate magic bullets for in vivo applications. They may theoretically improve tumor or pathogen targeting and minimize side effects, eventually replacing the full-length bispecific antibodies. Emphasizing on developmental methodology and clinical applications of bispecific antibodies, this review gives a bird's-eye view of these unique bioconjugates.

A new method to generate quadromas by electrofusion and FACS sorting

Bispecific monoclonal antibodies (bsMAbs) are unique molecules incorporating two different paratopes in a single antibody molecule. BsMAbs can be useful in different areas of research as well in clinical applications. Traditionally, bsMAbs are produced by hybrid-hybridomas that are generated by the fusion of two pre-established hybridomas. The development of such hybrid-hybridomas can be difficult and time-consuming. Here, we introduce a new technique to generate such hybrids, electro-FACS-fusion. In this procedure, before the electrofusion, one of the hybridomas is labeled with fluorescein isothiocyanate (FITC) and the other with tetramethylrhodamine isothiocyanate (TRITC). The mixture of cells is then electrofused, and cells exhibiting dual fluorescence are selected by fluorescence activated cell sorting (FACS). The fused cells are directly plated in microplates for clonal growth. Using this technique, we produced three new hybrid-hybridomas secreting bsMAb that could be used for the next generation of immunoassays.

Characterization of a unique anti-DNA hybridoma

We have previously described the isolation and in vitro binding properties of eight anti-DNA monoclonal antibodies (MAbs) from an MRL-lpr mouse. In light of recent reports that have indicated it is possible to isolate multiple MAbs from a single hybridoma, our pathogenic hybridoma, 11F8, was examined for evidence of similar phenomena. Chromosome counting suggested that 11F8 cells are unusual and might indeed be expressing multiple heavy and/or light chains. PCR, cloning, and sequencing of immunoglobulin heavy and light chains indicate that 11F8 displays expression of both gamma 2a and gamma 3 heavy chains at the DNA level. Flow cytometry and amino acid sequencing reveals that expression of multiple isotypes also occurs at the protein level but only a single heavy- and light-chain sequence is able to bind DNA. Based on these results, we conclude that 11F8 is an unusual hybridoma that secretes two distinct heavy and at least one light chain from a single cell, and may represent a trioma, a stable three-cell fusion.

A sensitive enzyme immunoassay of human thyroid-stimulating hormone (TSH) using bispecific F(ab')2 fragments recognizing polymerized alkaline phosphatase and TSH

Bispecific F(ab')2 fragments recognizing both human thyroid-stimulating hormone (TSH) and alkaline phosphatase (ALP) were prepared by disulfide bond exchange between F(ab')2 fragments of IgG1 monoclonal antibodies (mAbs) against TSH and ALP, and were purified to homogeneity by hydrophobic interaction HPLC. ALP was polymerized by glutaraldehyde, and a new sandwich enzyme-linked immunosorbent assay (ELISA) for TSH was developed by using the ALP polymers and bispecific F(ab')2 fragments against TSH and ALP. In this assay, the preparation of covalently linked enzyme-mAb conjugates was not needed, and the interaction of mAb with non-specific proteins was greatly reduced by the use of F(ab')2 fragments. The sensitivity for TSH was shown to increase in proportion to the degree of polymerization of ALP, and the lower detection limit obtained with the ALP trimer was 0.5 microU/ml. The sensitivity was 30 times or more higher than that of the conventional ELISA using covalently linked enzyme-mAb conjugates. The use of bispecific F(ab')2 permits the use of monomers and polymers of the signal enzyme and, thereby, regulates the sensitivity of the assay system.

Enzyme immunoassays using bispecific diabodies

BACKGROUND

Bispecific antibodies with a first binding specificity to a target antigen and a second to an enzyme have great potential in enzyme immunoassays. As bispecific antibodies are difficult to make, the use of recombinant bispecific antibody fragments may provide a breakthrough.

OBJECTIVES

To make bispecific antibody fragments directed against an enzyme and to demonstrate their application in enzyme immunoassays.

STUDY DESIGN

Bispecific antibody fragments were assembled as diabodies (Holliger P., Prospero T., Winter G. Proc. Natl. Acad. Sci. USA 90, 1993, 6444-6448) directed to an enzyme, E. coli beta-galactosidase, and to each of three target antigens, hen-egg lysozyme (HEL), carcinoembryonic antigen (CEA), and HIV gpl20 (HIV). The diabodies were then evaluated in immunoassays.

RESULTS

The HEL diabody was shown to recruit beta-galactosidase in a microtiter plate immunoassay in which diabody and enzyme were co-incubated with antigen, washed and enzyme substrate added. The CEA diabody was shown to detect CEA by immunocytochemical staining of transfected, CEA-expressing HeLa cells and of adenocarcinoma colon tissue sections, and the HIV diabody to detect gpl20 in immunoblots of total cell extracts.

CONCLUSION

The results illustrate the diagnostic potential of diabodies in enzyme immunoassays.

Bispecific multivalent antibody studied by real-time interaction analysis for the development of an antigen-inhibition enzyme-linked immunosorbent assay

A bispecific antibody with specificities for both 7-hydroxycoumarin (7-OHC) and alkaline phosphatase (AP) was produced by chemically cross-linking two parental polyclonal antibodies. Real-time interaction analysis of the bispecific multivalent antibody (bsMAb) was performed using BIAcore, a surface plasmon resonance (SPR)-based biosensor, in order to confirm its bispecific nature. A 7-OHC-BSA conjugate was covalently immobilized to a dextran matrix to serve as the reaction surface and unconjugated bovine serum albumin (BSA) was immobilized on to a separate dextran matrix as a control surface. Immunoaffinity-purified bsMAb, parental anti-7-OHC antibody and AP were injected over both surfaces. The bsMAb was shown to bind both antigens, 7-OHC and AP, simultaneously. Comparison of the ratio of mass bound for bsMAb and AP (5:1) with the ratio of the molecular masses of bsMAb (approximately 300 kDa) and AP (85 kDa) (3.5:1) suggests that most of the bsMAb species possess both specificities. The bsMAb was employed in a one-step antigen-inhibition ELISA for the detection of 7-OHC. The assay was compared with a conventional ELISA approach employing an AP-labelled secondary antibody. The bispecific antibody approach proved to be faster and more sensitive, with a detection limit of 6 ng ml-1 as compared with approximately 50 ng ml-1 for the conventional approach. The assay was used for the quantification of free and total 7-OHC in urine samples from two healthy volunteers who had been administered coumarin. The accuracy and precision of the assay were assessed. The bispecific antibody-based assay gave similar results, accuracy and precision, but proved to be far more sensitive (limit of determination 6 ng ml-1 for total 7-OHC). It is concluded that real-time interaction analysis using BIAcor provides a rapid method for the evaluation of the bsMAb and it was verified that the bispecific product formed by chemical cross-linking of two parental antibodies offers a simple alternative for the development of a highly sensitive ELISA.

Hybrid hybridomas producing bispecific antibodies to CEA and peroxidase isolated by a combination of HAT medium selection and fluorescence activated cell sorting

A combination of fluorescence-activated cell sorting and HAT medium selection has been used to establish bispecific antibody (biAbs)-producing hybrid hybridomas. For this purpose hypoxanthine-guanine phosphoribosyl transferase (HGPRT)-deficient mutants were isolated from a hybridoma line (D11-DG2) producing anti-CEA antibodies by 8-azaguanine treatment. The resulting HAT-sensitive hybrid cells were stained with the fluorescence marker tetramethyl rhodamine isothiocyanate (TRITC) and fused by polyethylene glycol (PEG) with HAT-non-sensitive unstained hybrid cells producing antibodies to horseradish peroxidase (POD). Fluorescent fused hybrid hybridomas as well as non-fused stained anti-CEA cells were separated from the unstained anti-POD cells using a fluorescent activated cell sorter (FACS). Finally, non-fused enzyme-deficient anti-CEA cells were eliminated by cultivation in HAT selection medium which permits only an outgrowth of HAT-resistant hybrid hybridoma cells containing the genes for producing both antibodies.

Bispecific IgA/IgM antibodies and their use in enzyme immunoassay

Two hybrid hybridomas secreting polymeric bispecific antibodies to human chorionic gonadotropin and calf intestinal alkaline phosphatase were produced by fusion of IgA- and IgM-secreting mouse hybridomas. Both hybrid antibodies were purified from ascitic fluid by size exclusion chromatography. An IgM-like fraction was shown to exhibit bispecific activity. Bispecificity was completely lost following mild reduction and alkylation. Both bispecific antibodies were used to develop a sensitive enzyme immunoassay for hCG.

The potential improvement of thrombolytic therapy by targeting with bispecific monoclonal antibodies: why they are used and how they are made

The generation of the proteolytic enzyme plasmin from its inactive precursor plasminogen, mediated by so called plasminogen activators, is the essential step in thrombolytic therapy. Plasmin is responsible for the degradation of the insoluble fibrin, the major component of a thrombus, to soluble fibrin degradation products. So far, the use of the more recently developed thrombolytic agents single-chain urokinase-type plasminogen activator (scu-PA) and tissue-type plasminogen activator (t-PA) were disappointing, mainly due to some of their negative properties in vivo, i.e., rapid inhibition and/or hepatic clearance. Besides some background information on the haemostatic balance; t-PA and scu-PA structure; and mechanisms of action, we here review some reported attempts to improve on these agents for thrombolytic therapy following various strategies. One of the more potential strategies, antibody-targeted thrombolytic therapy using bispecific monoclonal antibodies, is discussed somewhat more extensively, as are the several procedures that can be followed for bispecific antibody preparation.

Therapeutic effect of ansamitocin targeted to tumor by a bispecific monoclonal antibody

We have constructed a murine hybrid hybridoma that secretes a bispecific monoclonal antibody (mAb) by fusing a hybridoma secreting an anti-ansamitocins mAb with a hybridoma secreting an anti-human transferrin receptor (TfR) mAb that binds to human A431 epidermoid carcinoma cells. The bispecific mAb, reactive to both ansamitocins and TfR, was purified by a combination of hydrophobic column chromatography and hydroxyapatite high-performance liquid chromatography, and evaluated in in vivo experiments using human tumor cell-implanted nude mice. Ansamitocin P-3 targeted through one of the antigen combining sites of the bispecific mAb was potentially more effective in suppressing the growth of established A431 tumor xenografts implanted on nude mice than unconjugated ansamitocin P-3 or the immunoconjugate of ansamitocin P-3 and monospecific anti-ansamitocins antibody, and the targeted ansamitocin P-3 finally eradicated the tumor mass. The bispecific mAb also played an important role in reducing such undesirable side-effects of ansamitocin P-3 as the loss of body weight, the damage to liver functions and the decrease in the number of white blood cells.

Enzyme immunoassay techniques. An overview

In spite of the great variety of enzyme immunoassays (EIA) they can be classified into two groups 'analyte-observed' and 'reagent-observed' assays, depending on their reaction principle. The latter are favored by use of monoclonal antibodies and are characterized by a greater sensitivity, a larger measuring range, a lower susceptibility to disturbing influences. They can be used only for detection of macromolecules. For heterogeneous EIAs to be used on laboratory scale, simple adsorption of antigens and antibodies is still recommendable though affinity constants decrease by at least one order of magnitude and antibody density at the solid phase and analyte binding capacity are not parallel due to increasing steric hindrance. For this reason, the antibody with the higher affinity constant should therefore always be used as solid-phase antibody. Microparticles used as solid phase for heterogeneous assays, due to their very high binding capacity for the analyte and extremely short diffusion distances, guarantee 'one step' assays of only a few minutes. Of the limited number of enzymes suitable as markers in immunoassays, horseradish peroxidase is the enzyme of choice followed by alkaline phosphatase. Although enzyme and enzyme-labelled reagents are detectable by fluorogenic product measuring with a sensitivity, which is 10-1000 times higher than using chromogenic substrates, the sensitivity of the assays can be increased only by factor 2-10. Labelling enzymes cannot only be covalently bound to the antibody, but also via anti-enzyme antibodies. Pros and cons of the different methods of coupling the enzyme/anti-enzyme complex to analyte-containing immune complexes are discussed. Different EIA variants to detect specific antibodies are reviewed. Among them only capture EIAs permit precise isotype analysis of antibodies of a distinct idiotype. Homogeneous EIAs are widely spread for hapten determination but even variants based on proximal linkage are no alternatives to heterogeneous EIAs for determination of macromolecules. Different parameters are defined which permit to assess the quality of an immunoassay and which should be used in routine assays as internal controls in the laboratory.

Bifunctional antibodies and their potential clinical applications

Bifunctional antibodies are monovalent, bispecific, antibody-derived molecules. They have been produced by both chemical and biological means. They are thought to have several advantages over monoclonal antibodies in both immunotherapy and immunodiagnosis. Bifunctional antibodies have been shown to be efficient in the targeting of drugs, toxins, radiolabelled haptens and effector cells on to diseased tissues, primarily cancer cells. In addition, bifunctional antibodies have been used to develop novel immunoassays. The full potential of bifunctional antibodies has yet to be realised.

Immunoglobulins secreted by a hybrid-hybridoma: analysis of chain assemblies

In addition to the bispecific antibody, the hybrid-hybridoma 28.19.8 secretes antibodies monospecific for carcinoembryonic antigen (CEA) and antibodies monospecific for vinca alkaloids. By exhaustive affinity purification, the immunoglobulins isolated by Protein A chromatography from ascitic fluid have been fractionated into four populations, three of which are immunoreactive. Studies on these fractions by FPLC, SDS-PAGE, and a variety of ELISAs have shown that seven of the ten possible combinations of heavy and light chains exist as immunoreactive forms. The results suggest that the other three inactive combinations are also secreted by the hybrid-hybridoma.

Enhanced transfection of a bacterial plasmid into hybridoma cells by electroporation: application for the selection of hybrid hybridoma (quadroma) cell lines

A procedure was investigated to transduce a bacterial plasmid containing a specific drug resistance marker (pSV2-neo), into a hybridoma cell line using electroporation. The effect of several buffers and the form of plasmid DNA (circular or linearized) on the stable transfection frequency were examined. When complete cell culture medium (DMEM) was used as electroporation buffer, we observed a two-fold increase in post-pulse viability and a ten- to thirty-fold increase in the transfection frequency of pSV2-neo, as compared with HEPES buffered 0.15 M sodium chloride. Supplementing DMEM with fetal bovine serum (DMEM + FBS) had some beneficial effect on post-pulse viability of the cells after electroporation, but did not markedly increase stable transfection frequency as compared with DMEM alone. Furthermore, with DMEM + FBS, the intact plasmid was transfected as effectively as linearized PSV2-neo. However, when using HEPES buffered saline, the transfection frequency of pSV2-neo increased two-fold after linearization as compared with intact plasmid. The drug resistance was used successfully as a marker for the selection of hybrid hybridoma (quadroma) cell lines after fusing two different hybridoma cell lines, producing anti-fibrin and anti-plasminogen activator antibodies respectively. The quadroma cells produced bispecific antibodies that are capable of accumulating plasminogen activator on a fibrin surface.

Bifunctional antibodies: concept, production and applications

Immunoglobulins, or antibodies, are monospecific, bivalent antigen-binding molecules. Bifunctional antibodies are bispecific, with each arm binding to a different antigen, and may be produced by biological or chemical methods. Biological production involves the fusion of two monoclonal antibody-producing hybridomas or of an immunised spleen cell and a hybridoma. The resulting hybrid hybridomas (quadromas or triomas) secrete a mixture of parenteral monoclonal antibodies and bifunctional antibody. In chemical production, the parental monoclonal antibodies can be 'chopped up and reconstituted' to produce the bifunctional antibody only. Bifunctional antibodies have a variety of potential uses. They were originally proposed as an aid to cancer chemotherapy where one of the arms of the antibody would bind to a tumour marker and the other to a drug, toxin, or cytotoxic cell. Functional agents can thus be target directly onto tumour cells, accumulating with higher density, yet with reduced side effects for the patient. Further applications have been proposed involving enzyme immobilization and novel immunoassay techniques. This review describes developments that have taken place in bifunctional antibody technology to date.

Flow sorting of hybrid hybridomas using the DNA stain Hoechst 33342

A two-step sorting procedure with the fluorescence-activated cell sorter (FACS) is described for the selection of hybrid hybridomas producing bispecific monoclonal antibodies. Parental hybridoma cells were first labelled before fusion with fluorescein isothiocyanate (FITC) and tetramethyl rhodamine isothiocyanate (TRITC); heterofluorescent cells were recovered after fusion. After a period of growth in culture, the cells were then stained with the DNA-specific dye bis-benzimidazole Hoechst 33342 and sorted on the basis of their DNA content. The staining conditions (10 micrograms/ml of Hoechst 33342, 90 min incubation time at 37 degrees C) were found to be optimal for obtaining a well resolved DNA histogram with minimal effect on the growth properties of cells from different mouse hybridoma lines. Employing this method we have isolated hybrid hybridomas synthesizing bispecific monoclonal antibodies reacting with human low density lipoprotein and alkaline phosphatase from calf intestine.

Bispecific antibody: a tool for diagnosis and treatment of disease

Antibodies with two distinct binding specificities have great potential for a wide range of clinical applications as targeting agents for in vitro and in vivo immunodiagnosis and therapy, and for improving immunoassays. They have shown great promise for targeting cytotoxic effector cells, delivering radionuclides, toxins or cytotoxic drugs to specific targets, particularly tumour cells. We discuss potential applications of bispecific antibodies, the theoretical basis and problems associated with their production and purification, cell fusion and chemical conjugation techniques, and propose a new manufacturing strategy by genetic engineering. This approach has enormous potential applications for producing tailor-made bispecific antibodies, and will enable widespread clinical uses of these antibodies both for diagnostic purposes and therapy.

Suppression of well-established tumour xenografts by a hybrid-hybrid monoclonal antibody and vinblastine

The hybrid-hybrid monoclonal antibody 28-19-8 has specificity for the tumour-associated antigen carcinoembryonic antigen and the vinca alkaloids. This bifunctional antibody has been used to target unmodified vinblastine sulphate to well-established MAWI human tumour xenografts implanted in nude mice. The highly significant suppression of tumour growth achieved throughout treatment has also been sustained for over 2 months after the withdrawal of treatment. Histological examination of excised tumours from treated animals has shown profound changes in their morphology when compared with tumours from control animals. Cells in tumours that had started to grow again after withdrawal of therapy were shown still to express carcinoembryonic antigen, the target antigen recognised by the bispecific antibody.

Antibody mediated targeting of radioisotopes, drugs and toxins in diagnosis and treatment

The recent resurgence of interest in site specific delivery of radioisotopes, chemotherapeutic drugs and toxins for the diagnosis and treatment of cancer, and for the selective manipulation of the immune system, can be directly related to the need for improved diagnosis and the fact that for many cancers, for example lung, colon and gastric, the conventional treatments of surgery, radiotherapy and chemotherapy have reached a plateau in terms of the number of patients cured. To date, because of their specificity, the major emphasis has been on the use of antibodies as carriers and extensive in vitro, in vivo preclinical and clinical evaluation is underway. The aim of this article is to review recent progress, highlight avenues being explored to overcome limitations and to indicate new approaches that are evolving in antibody mediated targeting.

The FITC-anti-FITC system is a sensitive alternative to biotin-streptavidin in ELISA

In a model ELISA system alkaline phosphatase (AP) absorbed onto microtitre wells was employed as the target antigen. The antigen was then reacted with a monoclonal antibody to AP either unlabelled or labelled with (a) FITC and (b) biotin. The bound anti-AP was then detected with horseradish peroxidase (HRP) conjugates of polyvalent anti-mouse IgG, and the FITC and biotin anti-AP conjugates with HRP conjugates of a monoclonal anti-FITC or streptavidin respectively. The FITC-anti-FITC system proved to be of similar sensitivity to the biotin-streptavidin system detecting 140 amol compared to 350 amol of antigen. Both these methods of antigen detection were superior to the anti-mouse IgG reagent (2100 amol). In contrast to biotinylated antibodies, FITC-labelled antibodies are highly coloured and fluorescent. These features aid the preparation, purification and characterisation of conjugates. In addition, very low non-specific binding is encountered with enzyme conjugates of anti-FITC and this may confer an advantage over enzyme conjugates of avidin/streptavidin reagents.

The production and radioimmunoassay application of monoclonal antibodies to fluorescein isothiocyanate (FITC)

Monoclonal antibodies (MoAbs) were produced against the fluorescence marker fluorescein isothiocyanate (FITC). FITC was used as a hapten to label different proteins and the anti-FITC MoAbs were used to identify these labelled proteins in a solid-phase radioimmunoassay and in cellular radioimmuno-binding assays for the demonstration of antigens and antibodies.