IL-33 has the ability to attract and stimulate various immune cell populations within the glioma microenvironment, including CD8 + T cells, CD4 + T cells, dendritic cells (DCs), macrophages, and regulatory T cells (Tregs).17,51–53 We demonstrate that the absence of ST2 in the glioma microenvironment negatively impacts both the CD4+ and CD8+ T cell populations, by decreasing their activation or increasing their expression of checkpoint molecule PD1, respectively. Here, IL33 is linked to central nervous system cancer.