Bispecific IgA/IgM antibodies and their use in enzyme immunoassay

Production of bispecific antibodies

Bispecific antibodies (bsAbs) contain two different binding specificities within a single molecule and can specifically bind two different molecules together. BsAbs can be produced by chemically cross-linking purified antibodies or Fab fragments with reducible disulfide bonds or nonreducible thioether bonds, both of which are described in this unit. Protocols are also presented for producing BsAbs by fusing two antibody-producing hybridomas that can be selected for based on drug resistance, or by double labeling with fluorochromes and FACS. Support protocols describe screening and purification of bsAbs.

Cloning and characterization of a single chain antibody to glucose oxidase from a murine hybridoma

Glucose oxidase (GOD) is an oxidoreductase catalyzing the reaction of glucose and oxygen to peroxide and gluconolacton (EC 1.1.3.4.). GOD is a widely used enzyme in biotechnology. Therefore the production of monoclonal antibodies and antibody fragments to GOD are of interest in bioanalytics and even tumor therapy. We describe here the generation of a panel of monoclonal antibodies to native and heat inactivated GOD. One of the hybridomas, E13BC8, was used for cloning of a single chain antibody (scFv). This scFv was expressed in Escherichia coli XL1-blue with the help of the vector system pOPE101. The scFv was isolated from the periplasmic fraction and detected by western blotting. It reacts specifically with soluble active GOD but does not recognize denatured GOD adsorbed to the solid phase. The same binding properties were also found for the monoclonal antibody E13BC8.

Production and characterization of monoclonal antibodies against urea derivatives

A panel of monoclonal antibodies was generated against the urea-based hapten N-(2-N-chloroacetylaminobenzyl)-N'-4-chlorophenylurea as a tool for building up sensitive immune assays to detect urea derivatives and to screen them for catalytic antibodies (Abs). Eleven hybridomas were obtained that produced Abs reactive to the hapten. All Abs were of IgG class. Cross reactivities of the Abs to different haptens were examined, especially to a possible transition-state analog. Only four of the hybridomas (R2-DA10/F7, R2-GE7/H2, R2-HC2/A5, R2-HD6/F7) produced Abs crossreactive with the transition-state analog. From the 11 hybridomas, hybridoma B76-BF5 was chosen for further characterization. Compared to the other Abs, B76-BF5 showed the strongest binding and had a rather restricted specificity. These Abs could be used to build up a sensitive enzyme immunoassay for the detection of the hapten. All Abs were screened for crossreactivity with the pesticides monuron and diuron. No reactivity could be detected. In addition, the nucleotide sequences of the variable light and heavy chain genes of the similarly reactive Abs B76-BF5, B76-BB3, R2-DA10/F7, and R2-GA6/G3 were determined to clarify whether structure and binding specificity of these Abs showed any correlation.

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.

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.