Detection of malignant melanoma with monoclonal antibodies.

Eleven murine monoclonal antibodies (MoAbs) were isolated that defined unique membrane antigens expressed on human melanoma cells but not detectable on human lymphoid cells by radioimmunometric assays. Five of these MoAbs each identified a separate melanoma cell surface antigen as shown by distinctly different in vitro MoAb binding patterns to a diverse panel of tumor cell lines. One of these 5 monoclonals, MoAb 34.1, reacted specifically with 9/11 melanoma lines and 0/28 other human tumor or lymphoid cell lines. The other 4 MoAbs reacted strongly with melanomas, but also bound to 1 or more non-melanoma lines. The remaining 6 MoAbs defined three distinct regions of a single melanoma cell membrane protein with a molecular weight of 125 kiloDaltons (kD) as shown by antibody crossblocking and gel electrophoresis. A sensitive radioimmunoassay developed with MoAbs to 2 epitopes of this 125 kD protein detected up to 500-fold higher levels of this antigen in extracts of melanoma cells compared to autologous lymphoid cells. The 125 kD antigen also was detected by indirect immunoperoxidase assays with the MoAbs on biopsied tumors in histologic tissue sections of 5/11 metastatic melanomas and 1/11 carcinomas but was found on some normal endothelium and smooth muscle. Another monoclonal, MoAb 705, reacted more broadly with tumor cells in 10/14 biopsied melanomas and 10/11 carcinomas, but also was reactive with basal epidermis and normal fibroblasts. By contrast, MoAb 34.1 bound specifically to tumor cells of 7/11 biopsied metastatic melanomas, but bound 0/10 carcinomas and few normal tissues except for some macrophages. Thus, MoAb 34.1 was the most specific diagnostic reagent for immunohistologic detection of melanoma. The 250 kD antigen defined by MoAb 34.1 is similar to a high molecular weight proteoglycan reported to be an excellent tumor marker for human melanomas. The results of these studies show that murine monoclonal antibodies can be used as sensitive reagents for radioimmunoassays and immunohistology of malignant melanoma.