Abstract

GD3 is the most prominent ganglioside on the surface of human melanoma cells, and therefore it has been considered by several investigators as a potential tool for active immunotherapy of melanoma. The main obstacle to this goal is that GD3 is poorly immunogenic in mice and in humans. Several approaches have been described for increasing the GD3 immunogenicity. Here, the immunogenicity of GD3 ganglioside was investigated by vaccination of Balb/c x C57B1/6 F1 mice with several types of GD3-bearing liposomes. The humoral immune response was analyzed by ELISA and tumor cell recognition. Several liposome formulations were assayed in order to increase the immunogenicity of GD3. We also tested vaccinations with GD3-Salmonella minnesota, Freund's complete adjuvant and Bordetella pertussis antigen. Immunization of mice with sphingomyelin:cholesterol:dicetyl-phosphate:GD3, molar ratio 40:40:10:10, liposomes resulted in good IgM and IgG3 anti-GD3 response, with a maximum titer of 1:1200 and absence of significant cross-reactivity with other gangliosides. In immunofluorescence assays, the antisera induced showed high capacity of recognition of melanoma cells with no reactivity against other tumor cells. The results clearly showed a high positive correlation between liposomes with sphingomyelin and GD3 immunoreactivity. The incorporation of muramyl-dipeptide or Lipid A in the liposome formulation increased the secretion of IgM and IgG as well as the nonspecificity of the response.