A redirected Treg cell is endowed with specificity toward a selected target antigen or ligand. The cell contains a chimeric receptor polypeptide that is expressed in a single, continuous chain, with an extracellular recognition region displayed on the surface of the cell, a transmembrane region and an intracellular signaling region. The extracellular recognition region is specific for the selected target antigen or ligand. The intracellular signaling region includes a combination of T-cell signaling polypeptide moieties, which combination, upon binding of the extracellular recognition region to the selected target antigen or ligand, triggers activation of the redirected Treg cells to cause suppression of T-cell mediated immunity. Such redirected Treg cells may be used to suppress undesired activity of T effector cells thereby mediating an immune or inflammatory response. They are particularly useful in treating T effector cell-mediated diseases, such as inflammatory bowel disease, transplant rejection and GVH disease.