CXCR4 and nasopharyngeal carcinoma: LMP1 and EBNA1 expressed by NPC cells are able to induce PD-L1 up-regulation via STAT3 and NF-κB signaling, Treg recruitment via CXCL12-CXCR4 chemotaxis, as well as expansion of myeloid-derived suppressor cells (MDSCs) (31, 34, 35).