Glioblastomas induce them to adopt an activated phenotype; in cell culture, co-culture of glioblastoma cells with macrophages or microglia induces the latter to adopt an M2-like immunosuppressive phenotype, a process that is mediated by various cytokines including CSF-1, TGFβ, and GDF15 [77]. This evidence concerns the gene GDF15 and glioblastoma.