Butyrophilin 3A/CD277-Dependent Activation of Human γδ T Cells: Accessory Cell Capacity of Distinct Leukocyte Populations

Human V gamma 9V delta 2 T cells recognize in a butyrophilin 3A/CD277-dependent way microbial (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) or endogenous pyrophosphates (isopentenyl pyrophosphate [IPP]). Nitrogen-bisphosphonates such as zoledronic acid (ZOL) trigger selective gamma delta T cell activation because they stimulate IPP production in monocytes by inhibiting the mevalonate pathway downstream of IPP synthesis. We performed a comparative analysis of the capacity of purified monocytes, neutrophils, and CD4 T cells to serve as accessory cells for V gamma 9V delta 2 T cell activation in response to three selective but mechanistically distinct stimuli (ZOL, HMBPP, agonistic anti-CD277 mAb). Only monocytes supported gamma delta T cell expansion in response to all three stimuli, whereas both neutrophils and CD4 T cells presented HMBPP but failed to induce gamma delta T cell expansion in the presence of ZOL or anti-CD277 mAb. Preincubation of accessory cells with the respective stimuli revealed potent gamma delta T cell-stimulating activity of ZOL-or anti-CD277 mAb-pretreated monocytes, but not neutrophils. In comparison with monocytes, ZOL-pretreated neutrophils produced little, if any, IPP and expressed much lower levels of farnesyl pyrophosphate synthase. Exogenous IL-18 enhanced the gamma delta T cell expansion with all three stimuli, remarkably also in response to CD4 T cells and neutrophils preincubated with anti-CD277 mAb or HMBPP. Our study uncovers unexpected differences between monocytes and neutrophils in their accessory function for human gamma delta T cells and underscores the important role of IL-18 in driving gamma delta T cell expansion. These results may have implications for the design of gamma delta T cell-based immunotherapeutic strategies.