CD80 and cytomegalovirus infection: Although an elevated PD-L1 expression in EBV-positive samples has been reported in other studies35,36, our study shows that EBV or cytomegalovirus infection increases expression of genes encoding PD-L1, PD-L2, PD-1, CD80, CD86, CTLA-4, Tim-3, LAG3, and 4-1BB immune checkpoint genes together with other T-cell markers such as CD4 and CD8 in tumors along the gastrointestinal tract, including esophagus, stomach, and intestine.