ICOS was the highest expressed co-stimulatory immune checkpoint receptor and significantly higher in HCC (35.38% in CD8, 61.66% in CD4), and CCA (23.27% in CD8, 48.19% in CD4), compared to PDA patients (3.27% in CD8, 22.34% in CD4). The gene discussed is ICOS; the disease is cholangiocarcinoma.