Recruitment of GAMs into the microenvironment is driven by multiple chemokines secreted by gliomas, including monocyte chemotactic protein (MCP)-1 (19), MCP-3 (20), TME motif chemokine 12(CXCL12) (21), colony-stimulating factor (CSF-1) (22), glial cell-derived neurotrophic factor (GDNF) and granulocyte-macrophage colony-stimulating factors (23). Here, GDNF is linked to central nervous system cancer.