143 Identification of Neoantigen-specific CD8+ T Cells in Two Murine Orthotopic Glioblastoma Models Using Cancer Immunogenomics.

Johanns TM, Ward J, Wilson C, Kobayashi DK, Bender D, Fu Y, Alexandrov A, Artyomov MN, Miller CA, Mardis ER, Dunn GP
Neurosurgery 63 Suppl 1 158 08/01/2016


INTRODUCTION : Our understanding of how immune-based strategies designed to enhance T-cell activation might effectively control glioblastoma progression has been limited by our ability to identify and monitor tumor-specific T cells. The "cancer immunogenomics" approach has facilitated the search for tumor-specific antigens over the past 4 years by applying comprehensive cancer genomics to tumor antigen discovery. We applied this methodology to identify tumor-specific "neoantigens" in preclinical brain tumor models susceptible to checkpoint immunotherapy.

METHODS : The C57BL/6-derived GL-261 and VM/Dk-derived SMA-560 H-2b haplotype brain tumors underwent DNA whole exome and RNA sequencing. High-affinity candidate neoepitopes were predicted by using in silico computational approaches. Tumor-specific T-cell recognition was assessed using enzyme-linked immunospot (ELISPOT) and mutant-specific tetramer analyses of tumor-infiltrating lymphocytes from tumors injected subcutaneously and intracranially.

RESULTS : The GL-261 and SMA-560 tumors harbored 4644 and 2066 nonsynonymoous exome mutations, respectively, of which half were expressed. We applied H-2Db- and H-2Kb-specific neoantigen prediction algorithms to identify candidate tumor antigens. To validate the immunogenicity of these candidate neoantigens, we assessed tumor-specific T-cell responses of tumor-infiltrating lymphocytes harvested from GL-261 and SMA-560 tumors transplanted heterotopically and orthotopically into their respective syngeneic hosts. Using interferon-? ELISPOT and tetramer analysis, we confirmed H2-Db-restricted IMP3-D81N (GL-261) and ODC1-Q129L (SMA-560) as endogenous neoantigens that were functionally immunogenic. Neoantigen-specific T cells were detected within intracranial tumors as well as draining lymph nodes.

CONCLUSION : We credentialed the immunogenicity of 2 predicted high-affinity neoepitopes in well-studied orthotopic syngeneic preclinical brain tumor models, GL-261 and SMA-560. Furthermore, we identified tetramer-positive, antigen-specific T-cell populations within transplanted brain tumors and draining lymph nodes. We therefore extend cancer immunogenomics-based neoantigen discovery to glioblastoma models and establish a foundation to expand studies of the tumor-specific mutanome and explore fundamental mechanisms of T-cell activation in central nervous system immunobiology.

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