PDCD1 and cancer: Furthermore, RBP4 was positively correlated with immune checkpoints, such as VSIR, TIGIT, SIRPA, SIGLEC7, PDCD1, LILRB4, LILRB2, LAG3, HAVCR2, CTLA4, and BTLA, across many cancers, but it showed negative correlations with immune checkpoints in LIHC and TGCT (Figure 5D).