IFNA1 and neoplasm: USP18 is a potent inhibitor of IFN-I signal transduction and subsequent IFN-stimulated gene (ISG) expression.19 To investigate IFN-mediated changes in the TME to promote tumor growth, we generated myeloid-specific USP18-deficient mice by crossing conditional Usp18-KO mice (Usp18f/f) with LysM-Cre transgenic mice that express Cre recombinase in myeloid cells.24 Cre-mediated deletion was observed in the peritoneal macrophages (PMs) from Usp18f/fLysM-Cre+/+ mice, but not in those from Usp18+/+ (wild type [WT]) or Usp18f/fLysM-Cre−/− mice (Figure 1B).