TLR3 ligand induces a direct costimulatory effect on phoshoantigen stimulated human γδ T cells, but not on aminobisphosphonate-stimulated human γδ T cells

γδT cells expressing Vγ9 paired withVδ2 account for up to 95% of γδ T cells in the peripheral blood.1 These cells recognize phosphorylated, nonproteinaceous intermediates of the non-mevalonate pathway of the bacterial isoprenoid biosynthesis pathway (phosphoantigens).2 Additionally, the same subset of VγδVd2 T cells has been shown to be activated by therapeutically used aminobisphosphonate.3 Moreover, VγδVd2 T cells express MHC class I- or MICA/B (MHC class I related molecules)-specific natural killer-inhibitory receptors such as NKG2A and natural killer-activating receptors such as NKG2D, which can modulate reactivity towards e.g. phosphoantigens.4,5