Intriguingly, malignant glioma cells successfully graft in immunocompromised mice whereas benign glioma cells fail to engraft.65 Pan and colleagues65 discovered that the cause of the failure of benign cells to engraft is due to impaired microglia function, including reduced expression of the chemokine receptor Ccr2 and its ligand Ccl5 in the immunocompromised mice; accordingly, mice deficient in Ccl5 phenocopy T-cell-deficiency, as gliomas also fail to engraft in Ccl5 knockout mice. This evidence concerns the gene CCL5 and central nervous system cancer.