PDCD1LG2 and viral infectious disease: In EBV-positive STAD, cytomegalovirus-positive colon and rectum adenocarcinoma and EBV or cytomegalovirus positive stomach and esophageal carcinoma, we found that viral infection associates with high expression of PD-L1 or PD-L2, CD80, CD86, PD-1, CTLA-4, Tim-3, LAG3, and 4-1BB without integrating into the human genome.