T lymphocytes bearing the alpha-beta T cell receptor (TCR) but lacking CD4, CD8, and markers of natural killer (NK) cell differentiation, i.e., TCR(+)CD3(+)CD4(-)CD8(-), are known as double-negative (DN) T cells and are defined by their capability of inhibiting immune responses via directly killing effector T cells in an antigen specific fashion. Furthermore, DN Treg cells have been shown to develop regulatory activity after encountering specific antigens, partially mediated by the acquisition of MHC-peptide complexes from antigen presenting cells (APCs).