Human γδ T cells comprise a small percentage (1-5%) of circulating lymphocytes and exert potent cytotoxicity against a broad range of tumour cells in a major histocompatibility complex unrestricted manner, thus creating an attractive candidate for cancer immunotherapy.
Gamma-delta T cells can be activated and expanded upon treatment with nitrogen containing bisphosphonates such as zoledronic acid (ZOL), an agent widely used clinically to treat malignancy-associated bone loss. We and others have shown that ZOL inhibits the mevalonate pathway leading to the accumulation of phosphoantigens which are recognized by γδ T cells resulting in a significant increase to γδ T cell mediated cytotoxicity of tumour cells. Human γδ T cells expressing CD16 (FcγRIII) may be used in conjunction with the tumour targeting monoclonal antibody drozitumab, which targets the signalling death receptor DR5 for apoptosis induction. In this study we facilitated large scale ex-vivo expansion of cytotoxic γδ T cells using ZOL for use in adoptive immunotherapy and assessed the potential for γδ T cells to enhance antibody dependent cellular cytotoxicity (ADCC).
Peripheral blood mononuclear cells from patients were cultured with ZOL and IL-2 for 14 days to expand γδ T cells ex-vivo. Phenotypic analysis and cytotoxicity assays were measured by flow cytometry and LDH release, respectively.
Our results demonstrate that ZOL facilitated ex-vivo expansion of γδ T cells up to 90% and exerted potent cytotoxicity against a variety of cancer cells including breast, prostate, osteosarcoma, and multiple myeloma in vitro. In addition, pre-treatment of cancer cells with low concentration of ZOL sensitized tumour cells to rapid killing by γδ T cells and cooperated with drozitumab for enhanced cytotoxicity to levels reaching more than 90%.
Adoptive transfer of γδ T cells has the potential for cell-based immunotherapy, when used alone and in combination with drozitumab especially in cancer patients treated with ZOL.