IMMU-47. THE ANTIGENIC PROFILE OF MURINE AND HUMAN MEDULLOBLASTOMA

BACKGROUND Cancer immunogenomics represents a complementary approach to the application of genomics in developing novel immunotherapies. We performed a multi-faceted computer algorithm, the Open Reading Frame Antigen Network (O.R.A.N.), on medulloblastoma transcription profiles and predicted antigens across a broad array of antigen classes. METHODS Patient-specific HLA haplotypes were called via customized Optitype and Phlat algorithms. Preclinical models- sonic hedgehog driven (Ptch1) and Group 3 MYC-driven (NSC) medulloblastoma were derived from C57BL6 murine strain with known MHC haplotypes. Only expressed mutations such as single nucleotide variations, small indels, gene fusions, and personalized TAAs were used for antigenic epitope predictions. Patient-specific or murine tumor associated antigens (TAA) were selected only if expressed >1 transcript per million (TPM) in tumor and the standardized expression across a human tissue database (29 organs or sub-regions, n=9,141) or a mouse normal tissue database (ENCODE, n=99) was below 1 TPM, respectively. TAA sequences were passed through eight MHC class I and four MHC class II affinity algorithms. All epitopes were screened against a customized human or murine proteomic library to guarantee that epitopes were not shared by other expressed isoforms or genes. Immune deconvolution with single cell RNASeq integration was leveraged for teasing out medulloblastoma immunologic landscape. RESULTS MB patients harbor MHC-I restricted 1.9 SNV, 0.1 Indel, 0.5 gene fusions and MHC-II restricted 2.5 SNV, 0.1 Indel and 0.5 gene fusion. 79.4% patients have at least 1 neoantigen. 88.2% patients have at least one immunogenic TAA. Importantly, cancer testis antigens and previously unappreciated neurodevelopmental antigens were found expressed across all medulloblastoma subgroups. We predicted 6 neoantigens and 14 TAAs for murine NSC tumor and 19 neoantigens and 13 TAAs for Ptch1 tumor. CONCULSION: Using a custom antigen prediction pipeline, we identified potential human and murine tumor rejection antigens with important implications for development of medulloblastoma cellular therapies.

Heterologous prime-boost vaccination targeting MAGE-type antigens promotes tumor T-cell infiltration and improves checkpoint blockade therapy

BackgroundThe clinical benefit of immune checkpoint blockade (ICB) therapy is often limited by the lack of pre-existing CD8+ T cells infiltrating the tumor. In principle, CD8+ T-cell infiltration could be promoted by therapeutic vaccination. However, this remains challenging given the paucity of vaccine platforms able to induce the strong cytotoxic CD8+ T-cell response required to reject tumors. A therapeutic cancer vaccine that induces a robust cytotoxic CD8+ T-cell response against shared tumor antigens and can be combined with ICB could improve the outcome of cancer immunotherapy.MethodsHere, we developed a heterologous prime-boost vaccine based on a chimpanzee adenovirus (ChAdOx1) and a modified vaccinia Ankara (MVA) encoding MAGE-type antigens, which are tumor-specific shared antigens expressed in different tumor types. The mouse MAGE-type antigen P1A was used as a surrogate to study the efficacy of the vaccine in combination with ICB in murine tumor models expressing the P1A antigen. To characterize the vaccine-induced immune response, we performed flow cytometry and transcriptomic analyses.ResultsThe ChAdOx1/MVA vaccine displayed strong immunogenicity with potent induction of CD8+ T cells. When combined with anti-Programmed Cell Death Protein 1 (PD-1), the vaccine induced superior tumor clearance and survival in murine tumor models expressing P1A compared with anti-PD-1 alone. Remarkably, ChAdOx1/MVA P1A vaccination promoted CD8+ T-cell infiltration in the tumors, and drove inflammation in the tumor microenvironment, turning ‘cold’ tumors into ‘hot’ tumors. Single-cell transcriptomic analysis of the P1A-specific CD8+ T cells revealed an expanded population of stem-like T cells in the spleen after the combination treatment as compared with vaccine alone, and a reduced PD-1 expression in the tumor CD8+ T cells.ConclusionsThese findings highlight the synergistic potency of ChAdOx1/MVA MAGE vaccines combined with anti-PD-1 for cancer therapy, and establish the foundation for clinical translation of this approach. A clinical trial of ChadOx1/MVA MAGE-A3/NY-ESO-1 combined with anti-PD-1 will commence shortly.