Glioblastoma multiforme (GBM) is the most common primary brain tumor and despite some progress in its treatment, the prognosis remains very poor. MHC-independent γ9δ2T cell mediated adoptive immunotherapy is an attractive candidate for GBM, as these cells are highly cytotoxic to GBM. γ9δ2T cells can be extensively expanded in vivo and ex vivo and were shown in a pilot study to considerably prolong survival when infused to GBM patients. However, better understanding of the γ9δ2T cell activation and design of a consistently successful therapeutic protocol is needed to allow the development of such strategy.
In an attempt to evaluate the efficacy and feasibility of γ9δ2T cell-based immunotherapy for GBM we established an ex-vivo expansion protocol for γ9δ2T cells from the peripheral blood of 16 GBM patients. Following short term culture with zoledronate and a low dose of IL2, γ9δ2T cells expanded to clinically relevant amounts, e.g. 3000 fold. These cells are highly cytotoxic and express cytokines in response to GBM cell lines and autologous glioma cells. Moreover, pre-treatment with biphosphonates enhanced the response of γ9δ2T cells against GBM, whilst specific antibodies inhibited this response, suggesting that it is dependent on recognition of the intermediate products of the mevalonate pathway, isopentenyl pyrophosphate (IPP). Moreover, incorporation of temozolomide, the most commonly used and the most effective chemotherapy for GBM, contributed to sensitivity U251 cell line to lysis by γ9δ2T cells. Thus, our results shed more light on the GBM recognition mechanism of γ9δ2T cells and support the concept that these cells could be used for immunotherapy of gliomas.
