IFN-Dependent Down-Regulation of the NKG2D Ligand H60 on Tumors

In this study, we show that IFN-gamma or IFN-alpha reduce expression of H60 on 3'-methylcholanthrene (MCA) sarcomas from 129/Sv mice. As determined by flow cytometry using either NKG2D tetramers or NKG2D ligand-specific mAb, H60 was identified as the NKG2D ligand most frequently expressed on these sarcomas, and its expression was selectively down-regulated by either IFN-gamma or IFN-alpha in a manner that was dose- and time-dependent and reversible. Down-regulation occurred at the transcript level and was STAT1-dependent. It also had functional consequences. IFN-gamma-treated MCA sarcomas with high levels of H60 were resistant to killing by IL-2-activated NK cells. Resistance was not solely dependent on enhanced MHC class I expression but rather also required H60 down-regulation. IFN-gamma-treated tumor cells also displayed diminished capacity to down-regulate NKG2D on freshly isolated NK cells. Transplanted tumor cells reisolated from immunocompetent mice displayed reduced H60 expression and increased MHC class I expression compared with tumor cells that were either left unmanipulated or reisolated from mice treated with neutralizing IFN-gamma-specific mAb. This report thus represents the first demonstration that certain cytokines and specifically the IFNs regulate expression of specific NKG2D ligands on murine tumors. This process most likely helps to specify the type of immune effector cell populations that participate in host-protective antitumor responses.