Vaccination with minigenes encoding for novel 'self' antigens are effective in DNA-vaccination against neuroblastoma

The induction of T-cell mediated immunity against neuroblastoma is a challenge due to poor immunogenicity of this malignancy. Here, we demonstrate the induction of protective immunity in a syngeneic murine neuroblastoma model following vaccination with minigenes comprising of three novel natural MHC class I ligands. First, after immunoprecipitation of MHC class I from NXS2 cells, peptides were eluted and examined in tandem-MS analysis which lead to the identification of three novel natural MHC class I peptide ligands, TEALPVKLI from ribonucleotide reductase M2, NEYIMSLI from Ser/Thr protein phosphatase 2A and FEMVSTLI with unknown origin. Second, we constructed two different minigenes, one encoding for the three novel epitopes and the second for three known mTH derived epitopes with high predicted binding affinity to MHC class I by cloning them into the mammalian expression vector pCMV-3FUB. This lead to constructs with an ubiquitin-tag upstream the inserted epitopes in order to facilitate proteasomal degradation. Furthermore the epitopes were separated by a spacer peptide (AAY), which proved to be a preferential proteasome cleavage site. Third, we demonstrate the induction of protective immunity against neuroblastoma using an attenuated strain of Salmonella typhimurium as a carrier harboring pCMV 3FUb vectors encoding for the two minigenes. These findings establish proof of concept that disruption of self tolerance against neuroblastoma associated epitopes may be an effective adjuvant therapeutic strategy.