IFNG and viral infectious disease: While type I interferons are secreted by any cell type in response to viral infection, including the MSC, Interferon gamma (IFNγ) is a type II interferon that is produced by a limited number of immune cells like NK, NKT and T cells in response to virus infection [58] or, as we demonstrate, the carrier stem cells, particularly in some unfavorable allogeneic MHC-mismatch settings.