Human melanoma-specific oncofetal antigen defined by a mouse monoclonal antibody.

140.240, an IgG2a mouse monoclonal antibody raised against a cultured human melanoma cell line, was highly specific for melanoma cells as determined by direct and absorption analyses in a mixed hemadsorption assay. Supernatants of doubly cloned hybridomas producing antibody 140.240 reacted with all cultured and fresh melanomas tested but failed to react with a variety of carcinomas, sarcomas, lymphomas, leukemias and other tumors of neuroectodermal origin. This antibody did not react with B-lymphoid cell lines, ruling out HLA-DR specificity. Non-reactivity of antibody 140.240 with peripheral blood lymphocytes obtained from the donor of the immunizing melanoma line excluded the possibility of detecting histocompatibility antigens. Nevus cells were also non-reactive. However, antibody 140.240 did identify an antigenic determinant on tissue homogenates prepared from fetuses of 10-14 weeks' gestation. The antigen involved was shed by cultured melanoma lines and, by immunoprecipitation analysis of radiolabelled lysates, had a molecular weight of approximately 87kdal. Thus, the structure identified by monoclonal antibody 140.240 is a melanoma-specific oncofetal antigen.