Specific Requirements for Vγ9Vδ2 T Cell Stimulation by a Natural Adenylated Phosphoantigen

Human V gamma 9V delta 2 T lymphocytes recognize phosphorylated alkyl Ags. Isopentenyl pyrophosphate (IPP) was previously proposed as the main Ag responsible for V gamma 9V delta 2 T cell activation by cancer cells. However, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), a metabolite in which the isopentenyl moiety is linked to ATP, was reported in cells activated with aminobisphosphonates. The contribution of this compound to tumor-stimulatory activity was thus examined. ApppI induces selective expansion of V gamma 9V delta 2 T cells from PBMCs. In the absence of APCs, however, ApppI has little stimulatory activity on V gamma 9V delta 2 T cells, and optimal activation with ApppI requires addition of a nucleotide pyrophosphatase releasing IPP plus AMP. Thus, ApppI has no intrinsic stimulatory activity. Nevertheless, stimulation by ApppI is strengthened by the presence of APCs. Moreover, in contrast to IPP, ApppI can be efficiently pulsed on dendritic cells as well as on nonprofessional APCs. Pulsed APCs display stable and phosphatase-resistant stimulatory activity, indicative of Ag modification. HPLC analysis of tumor cell extracts indicates that latent phosphoantigenic activity is stored intracellularly in the V gamma 9V delta 2 cell-sensitive tumor Daudi and can be activated by a nucleotide pyrophosphatase activity. The presence of ApppI in Daudi cell extracts was demonstrated by mass spectrometry. Nucleotidic Ags such as ApppI are thus a storage form of phosphoantigen which may represent a major source of phosphoantigenic activity in tumor cells. The unique properties of ApppI may be important for the design of Ags used in anticancer immunotherapeutic protocols using V gamma 9V delta 2 cells. The Journal of Immunology, 2009, 183: 3848-3857.