Comparing murine glioblastoma models, Liu et al. found increased macrophage infiltration, tumor-infiltrating lymphocyte (TIL) dysfunction, and anti-PD-L1 therapy resistance in orthotopic CT2A versus GL261 tumors. Whole-exome and RNA sequencing identified 29 CT2A candidate neoantigens, of which 13 induced CD8+ T cell responses after vaccination, and three generated endogenous responses; stability of the peptide-MHC complex correlated with immunogenicity. Anti-PD-L1 therapy along with vaccination against the three identified peptides boosted neoantigen-specific CD8+ TILs and extended survival of CT2A-bearing mice.
Contributed by Alex Najibi
BACKGROUND: Although clinical trials testing immunotherapies in glioblastoma (GBM) have yielded mixed results, new strategies targeting tumor-specific somatic coding mutations, termed neoantigens, represent promising therapeutic approaches. We characterized the microenvironment and neoantigen landscape of the aggressive CT2A GBM model in order to develop a platform to test combination checkpoint blockade and neoantigen vaccination. METHODS: Flow cytometric analysis was performed on intracranial CT2A and GL261 tumor-infiltrating lymphocytes (TIL). Whole exome DNA and RNA sequencing of the CT2A murine GBM was employed to identify expressed, somatic mutations. Predicted neoantigens were identified using the pVAC-seq software suite and top-ranking candidates were screened for reactivity by IFN-gamma enzyme linked immunospot (ELISPOT) assays. Survival analysis was performed comparing neoantigen vaccination, alphaPD-L1, or combination therapy. RESULTS: Compared to the GL261 model, CT2A exhibited immunologic features consistent with human GBM including reduced alphaPD-L1 sensitivity and hypofunctional TIL. Of the 29 CT2A neoantigens screened, we identified neoantigen-specific CD8+ T cell responses in the intracranial TIL and draining lymph nodes to two H2-Kb restricted, Epb4H471L and Pomgnt1R497L, and one H2-Db restricted neoantigen, Plin2G332R. Survival analysis showed that therapeutic neoantigen vaccination with Epb4H471L, Pomgnt1R497L, and Plin2G332R, in combination with alphaPD-L1 treatment was superior to alphaPD-L1 alone. CONCLUSIONS: We identified endogenous neoantigen specific CD8+ T cells within a alphaPD-L1 resistant murine GBM and show that neoantigen vaccination significantly augments survival benefit in combination with alphaPD-L1 treatment. These observations provide important preclinical correlates for GBM immunotherapy trials and support further investigation into the effects of multi-modal immunotherapeutic interventions on anti-glioma immunity.
Author Info: (1) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Pr
Author Info: (1) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. (2) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. (3) Department of Biochemistry, University of Illinois, Urbana, IL. (4) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. (5) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. (6) Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri. (7) Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri. (8) Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri. The McDonnell Genome Institute, Washington University in St. Louis, St. Louis, Missouri. (9) Department of Biochemistry, University of Illinois, Urbana, IL. (10) Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri. The Alvin J. Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, Missouri. (11) Department of Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri. Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri. The Alvin J. Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, Missouri.
