PROJECT SUMMARY This Multiple Principal Investigator (MPI) Project proposal for the Pediatric Immunotherapy Network is focused on high-risk neuroblastoma, a diverse and enigmatic malignancy arising from the developing sympathetic nervous system that remains lethal in 50% of patients despite intensive multi-modal therapy. There is an urgent unmet need for developing novel therapeutic interventions to decrease the incidence of relapse, increase overall survival, and reduce devastating toxicities associated with standard therapy. The primary goal of this Project is to achieve improved outcomes for patients with high-risk neuroblastoma through the development of a personalized vaccination strategy targeting individualized neoantigens. The central hypothesis is that high-risk neuroblastomas, despite a low tumor mutation burden (TMB), harbor a sufficient number of neoepitopes through canonical and non-canonical mutations to identify, predict, and validate optimal neoantigen peptides to engineer effective multivalent personalized neuroblastoma vaccines. The motivation for the proposed research is the urgent need to improve survival and to decrease treatment-related morbidities for patients with high-risk neuroblastoma. Indeed, the majority of high-risk neuroblastoma patients achieve a remission with standard therapy, and here we seek to engage the adaptive immune system to eradicate residual disease and prevent relapse. We will test our hypothesis through the two Specific Aims: 1) define the neoantigen landscape of high- risk neuroblastoma patient and genetically engineered mouse model (GEMM) tumors; 2) develop and test a readily translatable personalized vaccination strategy. In Aim 1 we will both provide the proof-of-concept that a multivalent vaccine consisting of both CD4+ and CD8+ epitopes is feasible for each high-risk patient and also credential our GEMM system for preclinical vaccination trials in Aim 2. We will use an integrative proteogenomic approach to identify up to eight immunogenic peptides for each personalized vaccine. In Aim 2, we will test both preventative and therapeutic efficacy of self-assembling nanoparticle multivalent peptide vaccines using our GEMM system on the CB57BL/6 background, and then compare this vaccine platform to a new lipid-peptide polymer vaccine system optimized to deliver peptides to dendritic cells. This Project proposes an innovative experimental strategy to identify, prioritize, and validate neoantigens in high-risk neuroblastoma, and a clinically relevant neuroblastoma GEMM system for preclinical evaluation of neuroblastoma vaccines. The significance of the proposed Project is the creation and validation of a novel immunotherapeutic approach that has the potential to revolutionize high-risk neuroblastoma standard of care by providing durable cures and decreased therapy- related morbidity. The expected outcome of this collaborative MPI Project is to establish the preclinical proof-of- concept for a personaliz...