ISG15 and viral infectious disease: Interestingly, MSC are usually resistant to viral infection due to their expression of interferon (IFN) stimulated genes (ISG) such as IFITM (interferon-induced transmembrane family), IFI6, ISG15, SAT1, PMAIP1, p21/CDKN1A, and CCL2 that preempt viral infection (Wu et al., 2018).