Zoledronic acid renders human M1 and M2 macrophages susceptible to Vδ2+ γδ T cell cytotoxicity in a perforin-dependent manner

V delta 2(+) T cells are a subpopulation of gamma delta T cells in humans that are cytotoxic towards cells which accumulate isopentenyl pyrophosphate. The nitrogen-containing bisphosphonate, zoledronic acid (ZA), can induce tumour cell lines to accumulate isopentenyl pyrophosphate, thus rendering them more susceptible to V delta 2(+) T cell cytotoxicity. However, little is known about whether ZA renders other, non-malignant cell types susceptible. In this study we focussed on macrophages (M phi s), as these cells have been shown to take up ZA. We differentiated peripheral blood monocytes from healthy donors into M phi s and then treated them with IFN-gamma or IL-4 to generate M1 and M2 M phi s, respectively. We characterised these M phi s based on their phenotype and cytokine production and then tested whether ZA rendered them susceptible to V delta 2(+) T cell cytotoxicity. Consistent with the literature, IFN-gamma-treated Mfs expressed higher levels of the M1 markers CD64 and IL-12p70, whereas IL-4-treated M phi s expressed higher levels of the M2 markers CD206 and chemokine (C-C motif) ligand 18. When treated with ZA, both M1 and M2 M phi s became susceptible to V delta 2(+) T cell cytotoxicity. V delta 2(+) T cells expressed perforin and degranulated in response to ZA-treated M phi s as shown by mobilisation of CD107a and CD107b to the cell surface. Furthermore, cytotoxicity towards ZA-treated M phi s was sensitive-at least in part-to the perforin inhibitor concanamycin A. These findings suggest that ZA can render M1 and M2 M phi s susceptible to V delta 2(+) T cell cytotoxicity in a perforin-dependent manner, which has important implications regarding the use of ZA in cancer immunotherapy.