High expressions of immune checkpoint genes, e.g., CTLA-4 and PD-1, would aid tumors to escape from immune surveillance (Ribas and Wolchok, 2018), and the immune checkpoint therapies prolonged overall survival in many cancer types, including advanced melanoma and urothelial cancers (Robert et al., 2015; Horn et al., 2018; André et al., 2020). Here, PDCD1 is linked to cancer.