Sera of 22 individuals were examined for immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody to autologous cultured tumor cells. Reactive native IgM was detected by immune adherence in four, and IgG by Protein A hemadsorption in five, sera. Direct and absorption testing of these reactive sera against a range of normal and neoplastic cells revealed one each with specificity for a highly restricted melanoma cell surface antigen and common tumor-associated antigen of melanoma. Given this low prevalence of antibody, we then tested whether IgG antibody might be retrieved from circulating immune complexes in melanoma patients' sera. Acidification and ultrafiltration of sera from seven patients have enhanced detectable IgG binding to autologous cultured melanoma in six. Characterization of one reactive autologous antibody has detected a common antigen in eight of nine melanoma lines tested. This antibody also detected two neuroblastomas, one of two glioblastomas, one of two sarcomas, and one of two breast carcinomas. The common melanoma antigen detected in these tests may be related to the neuroectodermal, oncofetal differentiation antigens described by others with autologous or allogeneic IgM. Autologous antitumor antibody in circulating immune complexes may provide a source of antibody for serodiagnostic and therapeutic applications relevant to treatment modalities, such as plasmapheresis and plasma perfusion over Protein A in melanoma and other cancers.

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Supported by Grants CA-08341 and IN-31-V-4 from the National Cancer Institute and the American Cancer Society, respectively.

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