GM2, GD2, and GD3 gangliosides are expressed on the surface of human melanoma cells and represent potential targets for immunological control of melanoma growth by monoclonal antibodies and active immunization. The immunogenicity of GM2 was investigated by analyzing the humoral immune response of melanoma patients to vaccination with cell lines selected for high GM2 expression and with vaccines containing purified GM2. The whole-cell vaccine and vaccines containing purified GM2 and bacillus CalmetteGuerin (BCG) elicited GM2 antibody in a high proportion of patients, particularly in GM2/BCG-vaccinated patients pretreated with cyclophosphamide and given a GM2/BCG booster immunization. Vaccines containing purified GM2 and Salmonella minnesota R595 as the adjuvant were also effective, but only in patients pretreated with cyclophosphamide. GM2 antibodies in vaccinated patients were of the IgM class and were cytotoxic for GM2-positive targets in the presence of human complement.Gangliosides are prominent cell-surface constituents of melanoma and other tumors of neuroectodermal origin. Three gangliosides, the monosialoganglioside GM2 and the disialogangliosides GD2 and GD3, are of particular interest to tumor immunologists because of their potential as targets for passive immunization with monoclonal antibodies (mAbs) and for active immunization with cancer vaccines. Despite the presence of GM2, GD2, and GD3 in normal brain and other tissues (1), these gangliosides are immunogenic in mice and humans; mouse mAbs have been generated against GM2 (2), GD2 (3, 4), and GD3 (5-8), and human sera and human mAbs with reactivity for GM2 (9-12), GD2 (11,13,14), and GD3 (15) have been identified.Over the past decade we have immunized sequential groups of melanoma patients with a variety of melanoma cell vaccines (16)(17)(18)(19)(20). These vaccine trials were based on our seriological analysis of the humoral immune response of melanoma patients to cell-surface antigens of autologous and allogeneic melanomas (21), and each vaccine was constructed to contain melanoma surface antigens known to be immunogenic in humans. Although vaccinated patients readily produced antibody to HLA-related alloantigens and heterologous serum components in the vaccine, only rarely was antibody elicited to more restricted melanoma antigens, such as class 1 (unique), or GD2 or other class 2 (shared) melanoma antigens. In parallel vaccine studies in the mouse, we have identified immunizing procedures that facilitate the serological response to tumor antigens (22-24). In the case of GM2, immunization with GM2-expressing tumor cells or purified GM2 only infrequently induced GM2 antibody in mice, whereas vaccines containing GM2 with adjuvants such as bacillus Calmette-Gudrin (BCG) or Salmonella minnesota R595 were far more effective (24).In the present study, we have examined the immunogenicity of GM2-containing vaccines in stage III melanoma patients. Two types of vaccines were used: a whole-cell vaccine containing high levels of GM2 and vaccines con...