Human γδ T cells: From a neglected lymphocyte population to cellular immunotherapy: A personal reflection of 30 years of γδ T cell research

•γδ T cells account for approximately 5% of CD3+ T cells in the blood and frequently express a Vγ9Vδ2 T-cell receptor•Vγ9Vδ2 T cells recognize pyrophosphate molecules that are produced by bacteria but also by many tumor cells•Vγ9Vδ2 T cells kill a broad variety of different tumor cells in an HLA-nonrestricted fashion•Vγ9Vδ2 T cell activation and expansion can be manipulated pharmacologically, e.g. by nitrogen-containing bisphosphonates•Vγ9Vδ2 T cells are attractive candiates for cellular immuotherapy