CD8A and cytomegalovirus infection: Recent studies have shown that HCMV infection increases the expression of immune checkpoint genes encoding PD-L1, PD-L2, PD-1, CD80, CD86, Tim-3, LAG3, as well as other T-cell markers such as CD4 and CD8A in tumors along the gastrointestinal tract, including the esophagus, stomach, and intestine 83.