Development and characterization of antibodies to a nicked and hyperglycosylated form of hCG from a choriocarcinoma patient - Generation of antibodies that differentiate between pregnancy hCG and choriocarcinoma hCG

Human chorionic gonadotropin (hCG) exists in blood and urine as a variety o f isoforms one of which contains peptide bond cleavages within its beta-sub unit loop 2 and is referred to as nicked hCG (hCGn), This hCG isoform appea rs to be more prevalent in the urine of patients with certain malignancies and possibly in some disorders of pregnancy, Until now, only indirect immun oassays could be used to quantify hCGn, We report the development of two mo noclonal antibodies (MAbs) to a form of hCGn isolated from a choriocarcinom a patient. This hCG isoform was not only 100% nicked, but also contained 10 0% tetrasaccharide-core O-linked carbohydrate moieties in its beta COOH-ter minal region. Two-site immunometric assays have been developed using these new antibodies, B151 and B152. The former exhibits good specificity for hCG n independent of the source of the hCGn, the form excreted by choriocarcino ma patients or the form of hCGn from normal pregnancies. The latter antibod y, B152, is sensitive to the carbohydrate moieties and possibly other diffe rences in hCG isoforms, but is not for nicking of the beta-subunit. These t wo immunometric assays provide potential novel diagnostic tools for direct measurement of hCG isoforms which could not be accurately quantified earlie r before development of the assays using these newly generated antibodies.