Dual Face of Vγ9Vδ2-T Cells in Tumor Immunology: Anti-versus Pro-Tumoral Activities

V gamma 9V delta 2-T cells are considered as potent effector cells for tumor immunotherapy through directly killing tumor cells and indirectly regulating other innate and adaptive immune cells to establish antitumoral immunity. The antitumoral activity of V gamma 9V delta 2-T cells is governed by a complicated set of activating and inhibitory cell receptors. In addition, cytokine milieu in tumor microenvironment can also induce the pro-tumoral activities and functional plasticity of V gamma 9V delta 2-T cells. Here, we review the anti-versus pro-tumoral activities of V gamma 9V delta 2-T cells and discuss the mechanisms underlying the recognition, activation, differentiation and regulation of V gamma 9V delta 2-T cells in tumor immunosurveillance. The comprehensive understanding of the dual face of V gamma 9V delta 2-T cells in tumor immunology may improve the therapeutic efficacy and clinical outcomes of V gamma 9V delta 2-T cell-based tumor immunotherapy.