Abstract LB-354: Immune phenotyping of diverse syngeneic brain tumors identifies critical tumor micro-environmental differences

Immunotherapy has emerged as a promising approach to treat cancer, however, its efficacy in highly malignant brain-tumors, glioblastomas (GBM), is limited. Pre-clinical syngeneic mouse models are at the forefront of testing and understanding emerging novel immune based therapies prior to their translation in patients. We generated distinct imageable syngeneic GBM-tumor models and assessed tumor infiltrating immune cells from end-stage tumors by utilizing RNA sequencing, CyTOF (mass Cytometry by Time of Flight) and correlative immunohistochemistry. CyTOF facilitates multiparametric analysis of up to 40 different markers which is useful especially in the case of GBM where number of TILs is limiting. We identified immunologically-inert and active syngeneic tumor types and show that inert tumors have an immune-suppressive phenotype with numerous MDSCs (Ly6C+ CD11b+), exhausted CD8 T cells and fewer eosinophils. To mimic the clinical settings of first line of GBM treatment, we performed tumor resection in an immunologically inert tumor model. We show that tumor-resection invigorates an anti-tumor response via significant increase in CD8+ T cells, monocyte/macrophages and decrease in Ly6G+ myeloid cells. A comparative CyTOF analysis of resected-tumor samples from GBM patients and mouse GBM tumors showed stark similarities in one of the mouse GBM tumors tested. These findings guide informed choices for use of GBM models for immunotherapeutic interventions and offer a potential to facilitate immune-therapies in GBM patients. Citation Format: Jasneet K. Khalsa, Joshua W. Keegan, Nina Cheng, Joseph Driver, Ameen Chaudry, Wenya Linda Bi, James A. Lederer, Khalid Shah. Immune phenotyping of diverse syngeneic brain tumors identifies critical tumor micro-environmental differences [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-354.