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 a nd other tumours, together with its peculiar biological properties, makes t his glycolipid a unique target for cancer immunotherapy, B16 mouse melanoma expresses GM3 and constitutes an appropriate model for the development of novel GMS-based vaccines. Recently, we hydrophobically incorporated purifie d GM3 into the outer membrane protein complex from Neisseria meningitidis t o form very small size proteoliposomes (GM3/VSSP), We have examined the ant itumour properties of GM3/VSSP vaccine end compared it with GM3 incorporate d in very low density serum lipoproteins (GM3/VLDL), Immunization with four doses of GM3/VSSP vaccine (120 mug of ganglioside) plus Freund's adjuvant or Montanide ISA 51 significantly increased the overall survival of mice in oculated in the subcutis with 10(3) B16-F1 cells, whereas the GM3/VLDL immu nogen was ineffective. The non-transient character of tumour protection was confirmed in animals surviving the first challenge and re-inoculated with 5 x 10(3) cells. GM3/VSSP vaccine also reduced the subcutaneous growth of h ighly aggressive B16-F10 cells. The importance of ganglioside structure in the tumour-protective effect of GM3/VSSP vaccine was confirmed using GM3 co ntaining N-glycolylneuraminic acid, a ganglioside absent in melanoma cells. Immunostaining and enzyme-linked immunosorbent assay (ELISA) experiments s howed 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 vaccinati on with GM3/VSSP. The present data indicate the molecular specificity of GM 3/VSSP vaccine as well as the adjuvant-dependent and non-transient characte r of tumour protection in the B16 mouse model. These findings suggest that an appropriate GM3 vaccine may be capable of inducing prolonged tumour prot ection in melanoma patients. (C) 2001 Lippincott Williams & Wilkins.