Reduced Expression of the Mevalonate Pathway Enzyme Farnesyl Pyrophosphate Synthase Unveils Recognition of Tumor Cells by Vγ9Vδ2 T Cells

Human Vgamma9Vdelta2 T cells are characterized by a unique specificity for certain tumors (e.g., Daudi), cells presenting so-called phosphoantigens such as isopentenyl pyrophosphate (IPP), or cells treated with aminobisphosphonates. We now report conversion of hematopoietic and nonhematopoietic tumor cell lines into Vgamma9Vdelta2 T cell activators by means of short hairpin RNA-mediated knockdown of expression of the IPP-consuming enzyme, farnesyl pyrophosphate synthase (FPPS). FPPS knockdown cells activated Vgamma9Vdelta2 T cells, as measured by increased levels of CD69 and CD107a, killing of FPPS knockdown cells, and induction of IFN-gamma secretion. The IPP-synthesis-inhibiting drug mevastatin reduced Vgamma9Vdelta2 T cell activation by FPPS knockdown cells but not activation by the phosphoantigen bromohydrin pyrophosphate. In conclusion, our data support the concept of Vgamma9Vdelta2 T cells as sensors of a dysregulated isoprenoid metabolism and suggest therapeutic down-modulation of FPPS expression as an additional tool to target tumor cells to Vgamma9Vdelta2 T cell-mediated immunosurveillance.