CTLA4 and biliary tract cancer: Interestingly, DNA hypomethylating agents (that can increase HERv transcription, leading to increased antigen expression and up-regulation of CTLA-4 and PD-L1) and immunotherapy combinatory treatments are being tested in a phase I trial (ClinicalTrials.gov Identifier: NCT03257761), studying the combination of guadecitabine and durvalumab in patients with advanced liver, pancreatic, or biliary tract cancers.