Bisphosphonic acid acts as Gamma/Delta T cell activating antigen and has direct cytotoxic activity against pancreatic carcinoma cells

T cells bearing the Gamma9/Delta2 T cell receptor (TCR) constitute two to ten percent of peripheral blood T lymphocytes. They have recently raised much interest as non-MHC restricted effector cells against a variety of tumors. Gamma/Delta T cells are known to be stimulated by phosphoantigens without the need of professional antigen presenting cells. Furthermore, it is described that incubation with phosphoantigens increases their proliferation rate rapidly.

Apoptotic and anti-proliferative effects of two bisphosphonates (pamidronate and zoledronic acid) against eight different ductal pancreatic carcinoma cell lines were measured by Annexin-V/PI stain and MTT assay. Gamma/Delta T cells were enriched from peripheral blood of healthy donors and expanded by stimulation with anti-CD3 and IL-2. Cytotoxic activity of Gamma/Delta T cells of age of 14 days was tested against these cell lines. In the next step, we pulsed tumor cells prior to the ⁵¹Cr release assay with bisphosphonates.

Zoledronic acid induced even at lower concentrations inhibition of proliferation. Incubation with a 3 μM solution inhibits proliferation to 11–93%. Cell lines susceptible for this treatment had a higher apoptosis rate. Gamma/Delta T cells showed cytotoxic activity against pancreatic cell lines (cell lysis of 24–37% at an effector to target ratio of 80:1). Inhibition of proliferation correlated significantly with susceptibility against Gamma/Delta T cells (P < 0.003). Pulsing of target cells with bisphosphonates prior to the cytotoxicity assay increased the lysis rate (41–87%).

Zoledronic acid has even at concentrations which could be achieved by normal dosage an anti-proliferative and apoptotic effect. Cell lines which are susceptible for bisphosphonates were also susceptible for treatment with Gamma/Delta T cells. The efficacy of Gamma/Delta T cells could be further enhanced by pulsing tumor cells with bisphosphonates.

At least for some pancreatic carcinoma cells a bisphosphonate-based therapy maybe useful, particular in combination with adoptive transfer of Gamma/Delta T cells