Demonstration of a well-characterized tumor-associated antigen on melanoma cell surface

We have isolated and characterized a melanoma tumor-associated antigen (TAA) from the spent culture medium of a melanoma cell line. Its presence has been detected in 72% of different melanoma specimens but not in normal tissues. Because tumor antigens may stimulate or perhaps block immune reactions to cancer cells, their presence on the cell surface may be a critical factor influencing tumor growth. Therefore, to define further the immunobiological characteristics of melanoma TAA, this antigen was investigated by membrane immunofluorescence. Serum from a melanoma patient known to have a high anti-TAA antibody titer was absorbed quantitatively with lymphoblastoid cells autologous to the target melanoma cells to remove non-anti-TAA antibodies. The absorbed serum was reacted with three cultured melanoma cell lines, UCLA-SO-10 (M10), UCLA-SO-14(M14), and UCLA-SO-24 (M24). Of these cell lines, M10 and M14 are known to express the antigen as assessed by radioimmunoassay. Reaction of the antibody(s) to the antigen(s) on the melanoma cell surface was detected by fluoroscein-conjugated goat anti-human IgG. The reactivity of the absorbed serum was inhibited by preincubation with purified melanoma TAA. These results clearly demonstrate that melanoma TAA is expressed on the cell surface of cultured melanoma cells.