A purified GM3 ganglioside conjugated vaccine induces specific, adjuvant-dependent and non-transient antitumour activity against B16 mouse melanoma in vitro and in vivo

The presence of substantial amounts of GM3 ganglioside on human melanomas and other tumours, together with its peculiar biological properties, makes this glycolipid a unique target for cancer immunotherapy, B16 mouse melanoma expresses GM3 and constitutes an appropriate model for the development of novel GM3-based vaccines. Recently, we hydrophobically incorporated purified GM3 into the outer membrane protein complex from Neisseria meningitidis to form very small size proteoliposomes (GM3/VSSP). We have examined the antitumour properties of GM3/VSSP vaccine and compared it with GM3 incorporated in very low density serum lipoproteins (GM3/VLDL). Immunization with four doses of GM3/VSSP vaccine (120 μg of ganglioside) plus Freund's adjuvant or Montanide ISA 51 significantly increased the overall survival of mice inoculated in the subcutis with 10³ B16-F1 cells, whereas the GM3/VLDL immunogen was ineffective. The non-transient character of tumour protection was confirmed in animals surviving the first challenge and re-inoculated with 5 × 10³ cells. GM3/VSSP vaccine also reduced the subcutaneous growth of highly aggressive B16-F10 cells. The importance of ganglioside structure in the tumour-protective effect of GM3/VSSP vaccine was confirmed using GM3 containing N-glycolylneuraminic acid, a ganglioside absent in melanoma cells. Immunostaining and enzyme-linked immunosorbent assay (ELISA) experiments showed a high specificity of immune sera against GM3 and the presence of all four IgG subclasses, with a preponderance of IgG2b and IgG3. In addition, a strong anti-B16 complement-mediated cytotoxicity was induced by vaccination with GM3/VSSP. The present data indicate the molecular specificity of GM3/VSSP vaccine as well as the adjuvant-dependent and non-transient character of tumour protection in the B16 mouse model. These findings suggest that an appropriate GM3 vaccine may be capable of inducing prolonged tumour protection in melanoma patients.