Linking Cancer Metabolism and Innate Immunosurveillance: Modulation of Gamma-Delta T Cell-mediated Tumor Cell Recognition by the Key Metabolic Regulator AMPK

There is accumulating evidence demonstrating that gd T cells comprise an important arm of innate cancer immunosurveillance governed by intracellular accumulation of mevalonate pathway products. In contrast to optimized in vitro conditions, growing tumors in vivo are exposed to nutrient deprivation/hypoxia both activating the key energy metabolism regulator adenosine monophosphate activated protein kinase (AMPK). Upon activation, AMPK increase catabolic ATP-generating processes such as uptake and oxidation of glucose and fatty acids but inhibit ATP-consuming biosynthetic processes such as protein synthesis and cholesterol production (mevalonate pathway). This correlation prompted us to investigate the effects of AMPK activation (mimicked by the synthetic AMP-analogue 5-aminoimidazole-4-carboxamide riboside (=AICAR) or by the anti-diabetic drug metformin on tumor cell recognition by Vg9Vd2 T cells. We found that Vg9Vd2 T cells exhibited significant decreased up-regulation of activation markers in response to AICAR or metformin pre-treated target tumor cell lines (Daudi, RPMI 8226 and the farnesylpyrophphosphate synthase (FPPS)-knockdown cell line Raji AS22) as compared to untreated tumor cells. In addition, AMPK activation in tumor cells reduced the ability of Vg9Vd2 T cells to produce pro-inflammatory cytokines (IFN-g, TNF-a). As determined by phospho-specific flow cytometry analysis, either AICAR or metformin treatment resulted in increased phosphorylation and therefore inactivation of the AMPK target enzyme 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, subsequently lowering intracellular mevalonate pathway products critical for activation of Vg9Vd2 T cells. Thus, this data demonstrates for the first time an impact of cancer metabolism on immune recognition facilitating tumor escape.