The invention relates to a method of assessing whether a subject includes CD4+,CD25+ T cells that have been activated to a specific antigen. The method includes the steps of obtaining from the subject a sample of lymphocytes including CD4+,CD25+ T cells, incubating at least one portion of the sample of lymphocytes so as to promote, distinction of CD4+,CD25+ T cells that have been activated to the specific antigen from those CD4+,CD25+ T cells that have not been activated to the specific antigen, and thereafter determining whether CD4+,CD25+ T cells activated to the specific antigen are present in the sample. The invention further relates to methods of growing CD4+, CD25+ T cells that have been activated to a specific antigen in vitro and to methods of increasing tolerance in a subject using the CD4+, CD25+ T cells that have been grown in vitro.