Reactivity of monoclonal antibody DF3 with a high molecular weight antigen expressed in human ovarian carcinomas.

We have previously described the monoclonal antibody (MAb) DF3, prepared against a human breast carcinoma. MAb DF3 reacts with a high molecular weight glycoprotein detectable in human breast carcinomas and in human milk. Previous studies have demonstrated that DF3 antigen levels are elevated in the plasma of patients with breast and ovarian cancer. The present study has further examined the reactivity of MAb DF3 with human ovarian carcinomas. Immunoperoxidase staining demonstrated reactivity of MAb DF3 with 95% of benign, borderline, and malignant tumors (serous, mucinous, and endometrioid) of the ovary. Furthermore, malignant tumors contained cytoplasmic DF3 antigen while benign tumors expressed the antigen only on apical surfaces. Western blot analyses demonstrated that the MAb DF3 reactive ovarian antigen (DF3-O) was a glycoprotein with a heterogenous molecular weight ranging between 300,000 and 450,000. This antigen was detectable by immunofluorescence on the cell surface of five of six cultured human ovarian carcinoma cell lines. The extent of cell surface reactivity with MAb DF3 was equivalent to or greater than that obtained with MAb OC125, an antibody generated against coelomic epithelium and developmental amnion. Furthermore, uptake of 125I-labeled MAb DF3 by human ovarian carcinoma xenografts in athymic mice was 5.4- and 6.2-fold higher than the respective uptake noted in liver and control tumor (P = 0.031). These findings suggest that DF3-O antigen is similar if not identical to the antigen detected in human breast carcinomas by MAb DF3. Thus, MAb DF3 may be a useful reagent in immunodiagnostic evaluation of patients with ovarian cancer.