Among the features that distinguish type 1 innate lymphoid cells (ILC1s) from NK cells is a gene signature indicative of TGFb-family cytokine imprinting. To assess the impact of TGFb family cytokines on ILC1 differentation, we examined SMAD4- a transcription factor that facilitates the signaling pathway common to all TGFb family cytokines-was specifically ablated in ILCs and NK cells. While SMAD4 deficiency did not affect ILC1 differentation, NK cells paradoxically aquired an ILC1-like gene signature and were incapable of controlling tumor metastasis and viral infection. We used microarray to define the transcriptional differences between splenic NK cells from WT and SMAD4F/F x Ncr1-Cre mice. Overall design: Splenic NK cells (NK1.1+CD49b+CD3-CD19-) were sorted to purity for RNA extraction and hybridization on Affymetrix microarrays.