Antigen-presenting cells lead to severe T cell exhaustion in glioblastoma

Abstract Glioblastoma (GBM) is the most common primary brain cancer in adults and remains universally lethal. Median survival remains a bleak 15–17 months from time of diagnosis, calling for new therapeutic strategies. Current immunotherapeutic efficacy continues to be hindered by the robust immunosuppression of the GBM tumor microenvironment (TME). T cells, critical for tumor clearance, are particularly affected and many take on an exhausted phenotype within the tumor. We have previously observed significantly worse exhaustion in models of glioma relative to other solid tumor models, suggesting a TME-specific phenomenon. In an orthotopic murine model of GBM, T cell exhaustion was identified using surface expression of inhibitory ligands, PD1, TIM3, and LAG3. Functional status was examined using intracellular flow cytometry for IFNy, TNFa, and IL-2. We consistently observed T cell exhaustion among antigen-experienced tumor-specific CD8+ T cells, suggesting that tumor-imposed exhaustion is dependent upon T cells encountering their antigen. It remains undetermined, however, which cell within the GBM microenvironment provokes a uniquely severe T cell exhaustion phenotype. Using CRISPR-Cas9 gene editing, we modified tumor cells to lack antigen-presentation capacities and revealed persistence of T cell exhaustion. In contrast, when the same capacity was removed from infiltrating, hematopoietic cells, T cells in the GBM microenvironment were less exhausted and retained their function. This suggests antigen-presenting cells (APC) are critical for T cell exhaustion within GBM. Our findings uncover an important role for APCs in eliciting T cell exhaustion, which will provide novel interactions for targeted immunotherapies.