Ryan 

Glioblastoma (GBM) is a very aggressive and fast-growing brain cancer with a median survival of about 15 months. One of the fundamental treatments for GBM is radiation therapy (RT); however, GBM often relapses, and the mechanisms responsible for the recurrence remain poorly understood. One potential explanation is the induction of immune evasion, in which cancer cells activate the dysfunction of immune cells to escape recognition and elimination. In that context, we investigated whether TIMP-1/CD63 axis represents a mechanism of immune evasion in irradiated murine GBM, potentially through its effect on CD8+ T cells exhaustion. We quantified TIMP-1 levels in supernatants from three murine GBM cell lines upon radiation through enzyme-linked immunosorbent assays. Single-cell RNA sequencing of CD63+ cells from the tumor microenvironment of GBM revealed 13 distinct clusters representing both tumor and immune cells. Among the immune populations, several exhibited immunosuppressive phenotypes, including exhausted CD8+ T cells. Flow cytometry further confirmed the exhausted phenotype on CD63+ CD8+ T cells when co-cultured with irradiated GBM cells. Flow cytometry further demonstrated that CD63+ CD8+ T cells co-cultured with irradiated GBM cells exhibited a more pronounced exhausted phenotype than their CD63- counterparts. Additionally, both tumor-derived TIMP-1 and CD63 expressed on CD8+ T cells were upregulated in an RT dose-dependent fashion. Altogether, these results highlight the potential of the TIMP-1/CD63 axis as a novel mechanism of immune evasion in GBM.