CCL2 and glioblastoma: GBM cells secrete a spectrum of cytokines and chemokines—including CCL2, CXCL1, CXCL12, colony-stimulating factor 1 (CSF-1), and vascular endothelial growth factor (VEGF)—which interact with corresponding receptors on various myeloid cell types, thereby promoting their recruitment into the TME (Magod et al., 2021; Veglia et al., 2021; Zha et al., 2020; Atai et al., 2011; Bronte et al., 2016; Gao et al., 2021).