PDCD1 and Burkitt lymphoma: Since EBV latency establishment may require expression of only a single viral protein, EBNA1 (which mediates latent viral replication via the host DNA polymerase), and EBNA1 is known to be poorly recognized by the host immune response [64, 65], it is possible that PD-1/CTLA-4 blockade may be less effective at controlling tumors such as BL and gastric carcinoma that have type I latency.