A novel hydrophobized GM3 ganglioside/Neisseria meningitidis outer-membrane-protein complex vaccine induces tumor protection in B16 murine melanoma

Gangliosides are sialic acid-containing glycosphingolipids that have increa sed surface membrane expression on cancers of neuroectodermal origin. The p resent study was designed to investigate at a preclinical level the therape utic usefulness of a consistently immunogenic and safe conjugate vaccine in melanoma. We have examined a novel vaccine of GM3 monosialoganglioside hyd rophobically conjugated with the outer-membrane-protein complex from Neisse ria meningitidis plus Montanide ISA 51 in the B16 melanoma mouse model. B16 cell line is characterized by the predominant presence of ganglioside GM3 on the cell surface. Vaccines were administered i.m. in the quadriceps at 1 4-day intervals and B16 cells were injected in the subcutis of the right fl ank of C57BL/6 mice, 7 days after the fourth dose. Significant suppression of tumor growth and prolongation of survival were seen by immunization with GM3 vaccine in animals challenged with 5x10(3) or 10(3) live melanoma cell s. In addition, vaccination reduced tumor growth in animals challenged with 5x10(4) cells. The reactivity of serum IgG from vaccinated mice was examin ed by a sensitive immunoperoxidase assay on B16 tumor specimens. Most melan oma cells displayed a distinct positive staining associated with both cell membrane and cytoplasm. In accordance with the immunohistochemical staining s, the antisera of immunized mice reacted brightly against B16 melanoma cel ls in flow cytometry studies. Anti-sera also mediated complement-mediated c ytotoxicity and specific response could be totally ascribed to antibodies o f the IgG2b subclass. The present data suggest that GM3 vaccine may provide a useful immunotherapeutic strategy for melanoma.