CCL2 and renal cell carcinoma: Renal cell carcinoma, a typical immune-excluded tumor, is considered to lack the expression of some chemokines related to T cell recruitment, such as CXCL9, CXCL10, CXCL11, CXCL13, CX3CL1, CCL2, and CCL5, in its TME [37], but the specific mechanisms underlying this lack of chemokines remain unclear.