IDO1 and melanoma: The microenvironment of melanoma metastases that are likely to response to immunotherapy is characterized by the presence of lymphocytes and the expression of the inflammatory chemokines CCL2, CCL3, CCL5, CXCL9, CXCL10 and CXCL116 and the immunosuppressive factors indoleamine-2,3-dioxygenase (IDO), PD-L1 and FoxP37.