Induction of IgG antibodies against the GD2 carbohydrate tumor antigen by vaccination with peptide mimotopes.

The disialoganglioside GD2, a carbohydrate antigen, is expressed on all tumors of neuroectodermal origin, including melanoma, neuroblastoma, sarcoma and small cell lung cancer. Due to its specific expression on tumor surfaces, GD2 is an attractive target for immunotherapies. The mouse/human chimeric anti-GD2 mAb ch14.18 is already applied in melanoma and neuroblastoma trials as a passive immunotherapy. To establish an active immunotherapy alternative, we aimed to replace the poorly immunogenic ganglioside with immunogenic peptides. Previously, we used the ch14.18 antibody to select GD2 peptide mimics from a phage display library. In the present study, two mimics of the ch14.18 epitope were coupled to keyhole limpet hemocyanin and used for immunizing BALB/c mice. Induction of a specific humoral immune response towards the original antigen GD2, both purified and expressed on neuroblastoma and melanoma cells, could be demonstrated in ELISA, Western blot, and immunofluorohistochemistry. As the elicited antibodies were of the IgG isotype, the mimotope conjugates were capable of recruiting T cell help and inducing memory phenomena. In conclusion, we show that an epitope of the carbohydrate antigen GD2 can successfully be translated into immunogenic peptide mimotopes. Our immunization experiments indicate that GD2 mimotopes are suitable for active immunotherapy of GD2-expressing tumors.