Human Vγ2Vδ2 T cells monitor
isoprenoid metabolism by recognizing
(E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the
2-C-methyl-d-erythritol-4-phosphate pathway used by microbes, and
isopentenyl pyrophosphate (
IPP), an intermediate in the
mevalonate pathway used by humans. Aminobisphosphonates and alkylamines indirectly stimulate Vγ2Vδ2 cells by inhibiting
farnesyl diphosphate synthase (FDPS) in the
mevalonate pathway, thereby increasing
IPP/
triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester that directly stimulate. In this study, we further characterize stimulation by these compounds and define pathways used by new classes of compounds. Consistent with FDPS inhibition, stimulation of Vγ2Vδ2 cells by aminobisphosphonates and alkylamines was much more sensitive to
statin inhibition than stimulation by
prenyl pyrophosphates; however, the continuous presence of aminobisphosphonates was toxic for T cells and blocked their proliferation. Aminobisphosphonate stimulation was rapid and prolonged, independent of known Ag-presenting molecules, and resistant to fixation. New classes of stimulatory compounds-
mevalonate, the alcohol of HMBPP, and alkenyl
phosphonates-likely stimulate differently.
Mevalonate, a rate-limiting metabolite, appears to enter cells to increase
IPP levels, whereas the alcohol of HMBPP and alkenyl
phosphonates are directly recognized. The critical chemical feature of
bisphosphonates is the amino moiety, because its loss switched aminobisphosphonates to direct Ags. Transfection of APCs with
small interfering RNA downregulating FDPS rendered them stimulatory for Vγ2Vδ2 cells and increased cellular
IPP. Small interfering RNAs for
isopentenyl diphosphate isomerase functioned similarly. Our results show that a variety of manipulations affecting
isoprenoid metabolism lead to stimulation of Vγ2Vδ2 T cells and that pulsing aminobisphosphonates would be more effective for the ex vivo expansion of Vγ2Vδ2 T cells for adoptive
cancer immunotherapy.