Human Vγ9Vδ2 T cells can sense through their TCR tumor cells producing the weak endogenous phosphorylated antigen isopentenyl pyrophosphate (IPP), or bacterially infected cells producing the strong agonist hydroxyl dimethylallyl pyrophosphate (HDMAPP). The recognition of the phosphoantigen is dependent on its binding to the intracellular B30.2 domain of butyrophilin BTN3A1. Most studies have focused on pyrophosphate phosphoantigens. As triphosphate nucleotide derivatives are naturally co-produced with IPP and HDMAPP, we analyzed their specific properties using synthetic nucleotides derived from HDMAPP. The adenylated, thymidylated and uridylated triphosphate derivatives were found to activate directly Vγ9Vδ2 cell lines as efficiently as HDMAPP in the absence of accessory cells. These antigens were inherently resistant to terminal phosphatases, but apyrase, when added during a direct stimulation of Vγ9Vδ2 cells, abrogated their stimulating activity, indicating that their activity required transformation into strong pyrophosphate agonists by a nucleotide pyrophosphatase activity which is present in serum. Tumor cells can be sensitized with nucleotide phosphoantigens in the presence of apyrase to become stimulatory, showing that this can occur before their hydrolysis into pyrophosphates. Whereas tumors sensitized with HDMAPP rapidly lost their stimulatory activity, sensitization with nucleotide derivatives, in particular with the thymidine derivative, induced long-lasting stimulating ability. Using isothermal titration calorimetry, binding of some nucleotide derivatives to BTN3A1 intracellular domain was found to occur with an affinity similar to that of IPP, but much lower than that of HDMAPP. Thus, nucleotide phosphoantigens are precursors of pyrophosphate antigens which can deliver strong agonists intracellularly resulting in prolonged and strengthened activity.
Keywords: Butyrophilin; Cancer therapy; Gamma delta T lymphocyte; Innate immunity; Nucleotide.