Enzyme immunoassay for human chorionic gonadotropin using monoclonal antibodies elicited with a synthetic peptide.

We recently described the generation of mouse monoclonal antibodies directed against hCG using a synthetic peptide immunogen: the carboxy-terminal peptide (CTP) of beta-hCG. The CTP, residues 109-145, is a portion unique to hCG and is not present in other glycoprotein hormones. These monoclonal antibodies react with beta-hCG-CTP and whole hCG but do not react with hLH. In the present study, a two-site sandwich ELISA specific for hCG has been developed using these CTP-induced monoclonal antibodies. Two monoclonal antibodies were paired: beta-hCG-CTP-a6 was immobilized to give a hCG-specific solid phase, and a biotinylated monoclonal antibody against beta-hCG was used as the indicator antibody. This second antibody was introduced during the hCG-capture step because of its agonist effect on hCG-capture by beta-hCG-CTP-a6 solid phase. This ELISA system can detect 2.2 IU/l hCG in a serum-free medium and 10.4 IU/l in a medium containing 20% human serum. We did not observe any cross-reactivity with hLH up to concentrations of 5000 IU/l. The hCG-ELISA correlated well (r = 0.99) with a control RIA in an assay of 78 human sera from healthy males, pregnant or non-pregnant females and from patients with choriocarcinoma, hydatidiform mole, or teratocarcinoma.

Non-cross-reactive monoclonal antibodies to human chorionic gonadotropin generated after immunization with a synthetic peptide.

Noncross-reactive monoclonal antibodies specific for human chorionic gonadotropin (hCG) were obtained after pre-selection for submolecular specificity with a synthetic peptide immunogen. Mice were immunized with a synthetic peptide representing a segment unique to the beta-subunit of hCG (amino acid residues 109-145), conjugated to diphtheria toxoid. We then derived nine different hybridomas that secreted monoclonal antibodies reactive with both native hCG and isolated C-terminal peptide, after somatic cell hybridization of immune spleen cells with a nonsecretory myeloma cell line. None of the nine monoclonal antibodies, termed beta-hCG-CTPa1----a9, reacted with hLH, hFSH, or hTSH, although these pituitary hormones display extensive amino acid sequence homology with hCG. The noncross-reactive anti-beta-hCG monoclonal antibodies show apparent association constants on the order of 10(9) to 10(10) M-1. A sandwich-type enzyme-linked immunosorbent assay was set up with cut-off values of around 5 mIU/ml. These antibodies might have important implications for: a) improving the diagnosis and clinical management of pregnancy; b) monitoring the course of development of carcinomas which secrete the hormone, through in vitro assays or in vivo radioimmunodetection; c) evaluating the antibodies' therapeutic potential against such carcinomas; d) studying the biologic functions of the C-terminal segment of beta-hCG; and e) addressing the anti-fertility effect of antibodies raised against that segment.