Class 1 (unique) tumor antigens of human melanoma: partial purification and characterization of the FD antigen and analysis of a mouse polyclonal antiserum.

Serum antibodies from melanoma patient FD were previously shown to detect a unique antigenic specificity (FD) expressed only on the autologous tumor cells (SK-MEL-131) in culture. The FD determinant is carried by a Mr 90,000 glycoprotein (gp90) that binds to concanavalin A but not to lentil lectin or wheat germ agglutinin. After treatment with endo-N-acetylglucosaminidase H, the antigen no longer bound to concanavalin A. These and other properties indicate the gp90 carries mainly high mannose or hybrid N-linked carbohydrate chains. gp90 was partially purified from a detergent-solubilized membrane preparation by chromatography on DEAE-Sepharose, hydroxylapatite, chelating Sepharose, and lectin-agarose columns. Two-dimensional electrophoresis of the final preparation revealed three major components, one of which was identified as the FD antigen since it was specifically removed by precipitation with serum from patient FD. Immunization with the partially purified antigen preparation elicited anti-gp90 antibodies in two of four mice as demonstrated by sequential radioimmunoprecipitation experiments. Absorption experiments demonstrated that the mouse antibodies could, unlike human FD serum, be absorbed by a number of different cell types. Based on these results it is proposed that gp90 in SK-MEL-131 cells has two distinct epitopes, one, unique, detected by autologous FD serum, and another, common epitope or epitopes, detected by the polyclonal mouse sera. The common epitope(s) is present on gp90 in a variety of cells, including allogeneic melanomas and FD-B cells. These findings, which are compared with those on mouse tumor rejection antigens, have clear implications for the understanding of the nature of tumor antigens.