CCL2 and melanoma: A melanoma mouse transplant model also put forward an alternative mechanism of immunosuppression where PTEN-deficient tumors promoted recruitment of immunosuppressive cells such as macrophages, regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) through upregulation of monocyte chemoattractant protein-1 (MCP1/CCL2) and vascular endothelial growth factor (VEGF) [58].