TGFB1 and glioblastoma: Local immunosuppressive effects are mediated by the glioblastoma cells themselves, which can secrete immunosuppressive cytokines such as TGFβ [6], as well as indirectly via glioblastoma recruitment of regulatory T cells and various myeloid cell types, including microglia, macrophages and myeloid-derived suppressor cells [3, 7].