Characterization of a monoclonal antibody, KR-P8, that detects a new prostate-specific marker

This report characterizes a prostate-specific monoclonal antibody, KP-P8, which was prepared against the human prostate cell line PC3. The antigen detected by KR-P8 was identified on the surfaces of 90% of cells of the PC3 line, as well as on 67% of cells of the Du-145 prostate line, but it was absent from the surfaces of normal peripheral blood leukocytes and cells of a number of lymphoblastoid lines. As judged by immunoperoxidase staining techniques, KR-P8 reacted with the glandular epithelium of all specimens of normal, benign hypertrophic, and malignant prostate glands tested. However, no reactivity was noted with numerous other human tissues including normal bladder, lung, liver, kidney, testis, colon, parotid gland, thyroid gland, and spleen. These results indicate that the antigen detected by KR-P8 is prostate organ-specific. Competitive blocking studies showed that the antibody did not recognize the previously described prostate-specific antigen or the alpha-Pro-3 antigen described by other investigators. The KR-P8 antibody also did not bind to purified prostatic acid phosphatase. The presence of the KR-P8 antigen was demonstrated in cell-free preparations of dilute seminal plasma by radioimmunoassay, indicating that this antigen is secreted by the glandular cells of the prostate gland. The clinical significance of this marker was demonstrated by its ability to identify prostate metastases of the lymph node.