ADCYAP1 and hepatocellular carcinoma: Results showed that the VIP and ADCYAP1 were similar to VIPR1, which displayed a positive correlation with the infiltration level of NK cells, iDC, and TEM (Additional file 1: Fig. S1A–D), suggesting the possibility that altered expression of ligands and receptors may lead to the change in immune cell infiltration level and has a dramatic impact on HCC progression.