To characterize the antigen present on the surface of cultured human malignant melanoma, three monkey xenogeneic antisera were raised. After appropriate absorption with pooled human erythrocytes, peripheral blood leukocytes, and liver homogenate, no blood group or HLA reactivity was detectable. Analysis of melanoma antigenic specificity was performed by the mixed hemadsorption microassay on live monolayer cells in conjunction with quantitative microabsorption analysis. To eliminate reactivity against nonmelanoma lines, 2 of the 3 antisera required further absorption with cells of the KB oral carcinoma line. The absorbed antisera reacted with 9 of 10 long-term established lines, 3 of 3 short-term cultures of human malignant melanoma, and 1 of 10 nonmelanoma epithelial and fibroblastic cell lines. Absorption experiments using a variety of cultured cells and fresh tissue homogenates of adult human melanoma and nonmelanoma sources further substantiated the results obtained with the direct tests. While each melanoma line showed a differing degree and pattern of reactivity, the antisera were most reactive against their respective immunizing lines as revealed by both the direct tests and absorption analysis. By quantitative absorption analysis, no evidence for individually specific melanoma antigens was obtained. The only positive absorption with nonmelanoma adult tissues was obtained with a retinoblastoma cell line, indicating the presence of antigens shared by tumors of common neuroectodermal origin. Extensive absorption with two xenogeneic malignant melanoma (murine and porcine) homogenates, normal human adult skin, and spleen tissues, or Bacillus Calmette-Guérin failed to reduce the reactivity against melanoma-associated antigens. Further absorption with human fetal tissues of 8 to 20 weeks of gestation removed part but not all of the reactivity. These studies with xenogeneic monkey antisera provide evidence for the existence of common melanoma-associated antigens as well as distinct but shared human fetal antigens on human melanoma cells.
This is Paper 8 of the series, “Characterization of Human Malignant Melanoma Cell Lines.” The work was supported by the Medical Research Council of Canada and the Ontario Cancer Treatment and Research Foundation.