GD2 peptide mimotope DNA vaccines for anti-neuroblastoma immunotherapy

The tumor-associated antigen disialoganglioside-GD2 is expressed on neuroblastoma and melanoma and is an established target for immunotherapy. Carbohydrates and glycolipids are T cell-independent antigens (TI) and usually evoke a poor immune response in tumor-bearing hosts. In order to overcome T-cell independency, we identified peptides mimicking the structure of glycolipid GD2, i.e. GD2 mimotopes.

This was accomplished by biopanning experiments of a phage-display library displaying circular decapeptides (kindly provided by L. Mazziacchelli, Bern, Switzerland) against the human/mouse chimeric anti-GD2 antibody (Ab) ch14.18. Thirteen independent phage clones were identified which bind to ch14.18 with high specificity and harbor mimicry potential with GD2. The subsequent immunization strategy to break peripheral tolerance is based on the construction of DNA minigenes encoding for the two best mimotopes of the selection procedure, mimotope A (MA) and and mimotope D (MD), including a T cell epitope from HIV-1 gp 120 referred to as the T1 peptide. T1 is suggested to bind both MHC class I and class II and thus might stimulate the cellular arm of anti-tumor response.

The final minigens were generated by overlapping PCR, Klenow reaction and cloning into the leader sequence containing pSecTag2-A-Vector (pSA). Then, pSA-MA and pSA-MD were transferred into attenuated Salmonella typhimurium (SL 7207), which were already successfully used as oral vaccines for neuroblastoma antigens.

Based on these data, we test whether oral vaccination with pSA-MA and pSA-MD induces an anti-neuroblastoma immune response capable of eradicating spontaneous neuroblastoma metastases. Results will be presented at the meeting.