Zoledronate, a γδ T lymphocyte–activating agent, enhances NK-cell activation and cytotoxicity. (A) Purified NK cells were cultured for 96 hours in the presence of media, TU167 cells alone, TU167 + 10 μg/mL hIgG1 (isotype control), or TU167 + 10 μg/mL cetuximab. CD137 expression on CD56⁺ NK cells was analyzed by FACS. Two representative experiments are shown. (B) Whole PBMCs were incubated in the presence of media, 10 μg/mL rituximab, 15μM zoledronate, or a combination of rituximab with zoledronate. The expression of CD69 on gated CD3⁻CD56⁺ NK cells was analyzed by FACS 96 hours after initiation of the cultures. A representative of 3 independent experiments is depicted. (C) Whole PBMCs were cultured with media (circles) or zoledronate (squares). Alternatively, γδ T lymphocyte–depleted PBMCs were cultured with zoledronate (triangles) for 96 hours. NK cells were purified from the groups described. NK-cell direct cytotoxicity (left plots) or antibody-dependent cellular cytotoxicity (right plots) was measured in a standard 4-hour ⁵¹Cr-release assay against TU167 SCCHN or Ramos B-cell lymphoma targets. Data are presented as mean ± SD of triplicate samples and are representative of 2 independent experiments. *P < .05 compared with NK cells purified from γδ T lymphocyte–depleted cultures.