PDCD1 and viral infectious disease: Ultimately, given the role of the mechanisms and pathways of Wnt/β-catenin and PD-1/PD-L1 in carcinogenesis and tumor formation, both of these pathways, by affecting the c-MYC gene and consequently deactivating the functions of the T CD8+ cell, lead to tumor cells escaping from the immune system and ultimately resistant viral infection.