CCR4 and malignant glioma: CCL2 mRNA was expressed in all glioma cell lines and expression increased when exposed to Tregs but not to CD4 + helper T-cells.<h4>Conclusion</h4>Our study validates CCL2-CCR4 as a bi-directional Treg-glioma immunosuppressive and tumor-promoting axis in canine high-grade glioma.