Regulatory T cells play an important role in regulating immune responses.Recently,a novel immune Treg cell with phenotype TCRαβ + CD3 + CD4-CD8-NK1.1-was known as the Double-negative T cells (DNT).DNT cells are able to suppress CD4 + and CD8 + T cells,B cells as well as NK cells and dendritic cells(DCs) and play an important role in regulating immune responses in models of autoimmunity,infection,inflammatory disease,transplantation and tumor immunity.Now DNT cells have already become a hot point in the research of the immunotherapy.This article mainly introduces the possible sources of DNT cells and the mechanisms of their functions.