A method of identifying an antigen-specific regulatory T cell (Treg) from a subject is discussed wherein the method comprises quantitatively or qualitatively detecting co-expression of each of cell markers CD4, CD25 and CD134, or alternatively, each of cell markers CD8, CD25 and CD137, as well as one or more cell markers selected from the group of Treg cell markers consisting of CD39, CD73, CD127, CTLA-4 and Foxp3 on a cell in a suitable lymphocyte-containing sample from the subject in response to exposure to a target antigen. Also discussed are methods of isolating and expanding the identified antigen-specific Treg population, which may permit antigen-specific Treg cell therapy.