Monoclonal antibodies against human ovarian tumor associated antigen NB/70K: preparation and use in a radioimmunoassay for measuring NB/70K in serum.

Murine monoclonal antibodies (MCAs) against human ovarian tumor associated antigen NB/70K have been prepared. One of these MCAs, NB12123, was chosen for the development of a radioimmunoassay for measuring serum NB/70K levels. In this assay, the average NB/70K level in 75 normal, healthy controls was 11.9 activity units (AU) with an SD of 14.9 AU. The normal cut off value for this assay was set at 45 AU (mean +2 SD). 24 of 46 (52%) ovarian cancer patients, 7 of 18 (39%) patients with benign ovarian cysts or tumors and 3 of 85 (4%) control samples had elevated serum NB/70K levels. Comparison of NB/70K levels measured in the NB12123 assay with levels measured in an assay using a polyclonal antiNB/70K previously developed in our laboratory [13] indicated that although both assays had approximately the same percentage of positive ovarian cancer patient samples, there appeared to be no correlation between the absolute NB/70K levels measured by the two assays. The rank of ovarian cancer patient samples was also different for the two assays. Also, almost 40% of patients with benign ovarian cysts and tumors had elevated serum NB/70K levels as measured by the NB12123 assay as compared to 0% for the polyclonal assay. Reciprocal cross-blocking experiments, absorption studies, and immune precipitate analysis indicated that both the monoclonal NB12123 assay and the polyclonal antiNB/70K assay measured the same population of NB/70K molecules. However, the polyclonal antibody recognizes epitopes in addition to that recognized by NB12123. Taken together, these results suggest that the epitope recognized by NB12123 is not as specific for malignant ovarian tumors as the epitope(s) recognized by polyclonal antiNB/70K and/or that more than the one epitope detected by the MCA is responsible for the specificity for ovarian cancer of the polyclonal NB/70K assay. In spite of this, the greater sensitivity and range of the monoclonal NB12123 assay make it possible to monitor serum NB/70K levels in ovarian cancer patients. In four patients examined, the fluctuating serum NB/70K levels appeared to correlate well with clinical status.