IMPS-30NOVEL AND SHARED NEOANTIGEN FOR GLIOMA T CELL THERAPY DERIVED FROM HISTONE 3 VARIANT H3.3 K27M MUTATION

Abstract

Recent genetic studies have revealed that malignant gliomas in children and young adults often show shared missense mutations, which encodes the replication-independent histone 3 variant H3.3. Approximately 30 % of overall glioblastoma (GBM) and over 70% of diffuse intrinsic pontine gliomas (DIPG) cases harbor the amino-acid substitution from lysine (K) to methionine (M) at the position 27 of H3.3. T-cells are normally tolerant to wild-type self-proteins, but can recognize mutated peptide epitopes as non-self. Hence, tumor-specific missense mutations can be suitable targets (i.e. neoantigens) for cancer immunotherapy. We evaluated whether H3.3-derived peptides that encompass the H3.3 K27M mutation can induce specific cytotoxic T lymphocyte (CTL) responses in human leukocyte antigen (HLA)-A2+ CD8+ T-cells. Four candidate peptides encompassing different amino-acid positions around the H3.3 K27M mutation were synthesized, and peptide-specific CTL lines and clones were generated from peripheral blood mononuclear cells of HLA-A2+ donors by in vitro stimulation with each of the synthetic peptides. One of the 4 peptides (the H3.3.K27M epitope, hereafter) induced CTL lines which recognized not only the synthetic peptide loaded on T2 cells but also lysed HLA-A2+ DIPG cell lines which endogenously harbor the H3.3.K27M mutation. On the other hand, CTL lines did not react to HLA-A2+, H3.3 K27M mutation-negative cells or HLA-A2-negative, H3.3 K27M mutation+ cells. Furthermore, CTL clones with high and specific affinities to HLA-A2-H3.3.K27M-tetramer were successfully obtained, and α- and β-chain cDNAs from high-affinity T cell receptor (TCR)s were cloned into a lentiviral vector. Additional studies are underway to determine antigen specificity, key epitope residues in the epitope and possible cross-reactivity to naturally existing variants using T-cells transduced with the lentiviral vector encoding the TCR. These data provide us with a strong basis for developing peptide-based vaccines as well as adoptive transfer therapy using autologous T-cells transduced with the TCR.