Serological survey of normal humans for natural antibody to cell surface antigens of melanoma.

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Abstract
Sera of 106 normal adult men were tested for antibodies reacting with cell surface antigens of 3 established lines of cultured malignant melanoma. Positive reactions with a protein A assay for Ig[immunoglobulin]G antibodies were extremely rare (1-2%). The frequency of positive reactions with assays for IgM antibodies was higher: 5-15% in immune adherence assays and 55-82% in anti-C3 [complement component 3] mixed hemadsorption assays. Serum containing IgG antibody was obtained from a healthy 65 yr old Caucasian man; titers of antibody in his serum ranged from < 1/10 to 1/40,000 in tests with different melanoma cell lines. This IgG antibody identifies a differentiation antigen of melanocytes, provisionally designated Mel 1, that distinguishes 2 classes of melanomas: 22 melanoma cell lines typed Mel 1+ and 17 typed Mel 1-. Mel 1 is expressed by fetal fibroblasts but not adult fibroblasts and was found on 5 of 23 cultured epithelial cancer cell lines but not on glioma or B [bone marrow-derived]-cell lines. The melanoma antigens detected by the naturally occurring IgM antibodies are serologically unrelated to Mel 1 but, like Mel 1, appear to be differentiation antigens that distinguish subsets of melanoma. These IgM antibodies detect antigens that are identical or closely related to the AH antigen, a melanoma surface antigen that was initially defined by autologous antibody in a patient with melanoma. In view of the immunogenicity of Mel 1 and the AH antigens in humans and their occurrence or > 50% of melanomas, it remains to be seen whether antibody to those antigens can be elicited by specific vaccination of seronegative melanoma patients and whether this will have an influence on the clinical course of the disease.