USP7 and viral infectious disease: Although USP7 was originally identified through its interaction with ICP0 (infected cell polypeptide 0), a herpes viral protein, USP7 has been shown to play a key role in regulating the stability of tumor suppressor p53 and its E3 ubiquitin ligase, mouse double minute 2 homolog (MDM2), as well as proteins involved in multiple cellular pathways including various aspects of the cell cycle, immune response, cell survival, development, tumorigenesis, and viral infection (31, 32, 33, 34, 35, 36).