CTLA4 and lung cancer: Meanwhile, EBV has been reported to upregulate the expression of immune checkpoint proteins, such as programmed cell death 1 (PD-1), programmed death ligand 1 (PD-L1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and lymphocyte activation gene 3 (LAG3), which strongly facilitate the immuno-evasion capacity of lung cancer [55].