Further validation was performed using Nbs1f/f cell lines in which the de-ISGylase, Usp18, was disrupted via CRISPR-Cas9 editing and an exogenous doxycycline inducible 6HIS-ISG15 integrated via lenti-viral infection (Usp18−/−+6his-ISG15). This evidence concerns the gene ISG15 and viral infectious disease.