A method for expanding a population of γδ T-cells is provided in which isolated activated Peripheral Blood Mononuclear Cells (PBMCs) are cultured in a medium comprising transforming growth factor beta (TGF-β) under conditions in which the production of effector yδ T-cells having therapeutic activity against malignant disease is favored. The use of TGF-β in the production of effector cells in particular vγ9vδ2 T-cells is also described and claimed.
