Human Vγ9Vδ2 T cells recognize phosphorylated nonpeptide Ags (so called phosphoantigens), certain tumor cells, and cells treated with aminobisphosphonates. NKG2D, an activating receptor for NK cells, has been described as a potent costimulatory receptor in the Ag-specific activation of γδ and CD8 T cells. This study provides evidence that Vγ9Vδ2 T cells may also be directly activated by NKG2D. Culture of PBMC with immobilized NKG2D-specific mAb or NKG2D ligand MHC class I related protein A (MICA) induces the up-regulation of CD69 and CD25 in NK and Vγ9Vδ2 but not in CD8 T cells. Furthermore, NKG2D triggers the production of TNF-α but not of IFN-γ, as well as the release of cytolytic granules by Vγ9Vδ2 T cells. Purified Vγ9Vδ2 T cells kill MICA-transfected RMA mouse cells but not control cells. Finally, DAP10, which mediates NKG2D signaling in human NK cells, was detected in resting and activated Vγ9Vδ2 T cells. These remarkable similarities in NKG2D function in NK and Vγ9Vδ2 T cells may open new perspectives for Vγ9Vδ2 T cell-based immunotherapy, e.g., by Ag-independent killing of NKG2D ligand-expressing tumors.

We have investigated interferon-κ (IFN-κ) regulation in the context of human papillomavirus (HPV)-induced carcinogenesis using primary human foreskin keratinocytes (HFK), immortalized HFKs encoding individual oncoproteins of HPV16 (E6, E7, and E6/E7), and cervical carcinoma cells. Here, IFN-κ was suppressed in the presence of E6, whereas its expression was not affected in HFKs or E7-immortalized HFKs. Transcription could be reactivated after DNA demethylation but was decreased again upon drug removal. Partial reactivation could also be accomplished when E6 was knocked down, suggesting a contribution of E6 in IFN-κ de novo methylation. We identified a single CpG island near the transcriptional start site as being involved in selective IFN-κ expression. To prove the functional relevance of IFN-κ in building up an antiviral response, IFN-κ was ectopically expressed in cervical carcinoma cells where protection against vesicular stomatitis virus-mediated cytolysis could be achieved. Reconstitution of IFN-κ was accompanied by an increase of p53, MxA, and IFN-regulatory factors, which was reversed by knocking down either IFN-κ or p53 by small interfering RNA. This suggests the existence of a positive feedback loop between IFN-κ, p53, and components of IFN signaling pathway to maintain an antiviral state. Our in vitro findings were further corroborated in biopsy samples of cervical cancer patients, in which IFN-κ was also downregulated when compared with normal donor tissue. This is the first report showing an epigenetic silencing of type I IFN after HPV16 oncogene expression and revealing a novel strategy on how high-risk HPVs can abolish the innate immune response in their genuine host cells. [Cancer Res 2009;69(22):8718-25]