TNFRSF9 and nasopharyngeal carcinoma: Treg_C4_TNFRSF4 cells featured with high expression of TNFRSF family genes (TNFRSF4, TNFRSF9, and TNFRSF18) as well as CCR8 and exhibited the strongest immune-suppressive function compared to other Treg cell clusters in NPC.