Brain cancers are the leading cause of cancer related mortality in children and young adults with median overall survival of 9-10 months and hence represents a significant unmet medical need. Genome-wide sequencing efforts of pediatric gliomas have identified a recurrent and shared missense mutation in the gene encoding the replication-independent variant of histone 3, H3.3. Approximately 70% of diffuse intrinsic pontine gliomas (DIPG) and 50% of thalamic and other midline gliomas harbor the amino acid substitution from lysine (K) to methionine (M) at the position 27 of H3.3 gene. Tumor specific missense mutations are not subjected to self-tolerance and can be suitable targets (neoantigens) for cancer immunotherapy. Herein, we evaluated whether the H3.3K27M mutation can induce specific cytotoxic T lymphocyte (CTL) response in HLA-A2+ T cells. In vitro stimulation of HLA-A2+ donor derived CD8+ T cells with a synthetic peptide encompassing the H3.3K27M mutation (H3.3K27M epitope) induced CTL lines which recognized not only T2 cells loaded with the synthetic H3.3K27M epitope peptide but also lysed the HLA-A2+ DIPG cells which endogenously harbor the H3.3K27M mutation. On the other hand, the CTL lines did not react to either HLA-A2+ but H3.3K27M- negative DIPG cell lines or H3.3K27M positive but HLA-A2 negative DIPG cells. The H3.3K27M epitope peptide but not the non-mutant counterpart indicated an excellent binding affinity (Kd 151nM) to HLA-A2 based on competitive binding inhibition assay. From CTL clones with high and specific affinities to HLA-A2-H3.3K27M-tetramer, cDNAs for T cell receptor (TCR) alpha and beta chains were cloned into a retroviral vector. Human HLA-A2+ T cells transduced with the TCR demonstrated antigen specific reactivity as well as anti-glioma responses in vitro. Peptide titration assays suggested that the H3.3K27M specific TCR had the half-maximal reactivity for peptide recognition of around 100nM. Furthermore, critically important for safety of clinical application, alanine scanning demonstrated that the key amino acid sequence motif in the epitope of the TCR reactivity is not shared by any known human protein. Finally, intravenous administration of T cells transduced with H3.3K27M specific TCR significantly inhibited the growth of intracranial HLA-A2+ H3.3K27M positive glioma xenografts in immune deficient NSG mice. 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 H3.3K27M specific TCR.

Acknowledgements: This study is supported by the NIH/NINDS (1RO1NS096954), V Foundation and Parker Institution for Cancer Immunotherapy.

Citation Format: Zinal Chheda, Gary Kohanbash, John Sidney, Kaori Okada, Naznin Jahan, Diego Carrera, Payal Watchmaker, Kira Downey, Shuming Liu, Shruti Shrivastav, Sabine Mueller, Ian F. Pollack, Angel M. Carcaboso, Alessandro Sette, Yafei Hou, Hideho Okada. Identification of a novel and a shared H3.3K27M mutation derived neoantigen epitope and H3.3K27M specific TCR engineered T cell therapy for glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3767. doi:10.1158/1538-7445.AM2017-3767