BTLA and esophageal squamous cell carcinoma: Immunosuppressive gene analysis revealed that the DDRG signature was positively correlated with BTLA, CTLA4, HAVCR2, IL10RB, PDCD1LG2, and TIGIT, particularly PDCD1LG2, which may provide clues for acting as a potential immune target to enhance antitumor effects in ESCC.