Ex Vivo Isolation and Characterization of Cd4⁺Cd25⁺ T Cells with Regulatory Properties from Human Blood

It has been known for years that rodents harbor a unique population of CD4⁺CD25⁺ “professional” regulatory/suppressor T cells that is crucial for the prevention of spontaneous autoimmune diseases. Here we demonstrate that CD4⁺CD25⁺CD45RO⁺ T cells (mean 6% of CD4⁺ T cells) are present in the blood of adult healthy volunteers. In contrast to previous reports, these CD4⁺CD25⁺ T cells do not constitute conventional memory cells but rather regulatory cells exhibiting properties identical to their rodent counterparts. Cytotoxic T lymphocyte–associated antigen (CTLA)-4 (CD152), for example, which is essential for the in vivo suppressive activity of CD4⁺CD25⁺ T cells, was constitutively expressed, and remained strongly upregulated after stimulation. The cells were nonproliferative to stimulation via their T cell receptor for antigen, but the anergic state was partially reversed by interleukin (IL)-2 and IL-15. Upon stimulation with allogeneic (but not syngeneic) mature dendritic cells or platebound anti-CD3 plus anti-CD28 the CD4⁺CD25⁺ T cells released IL-10, and in coculture experiments suppressed the activation and proliferation of CD4⁺ and CD8⁺ T cells. Suppression proved IL-10 independent, yet contact dependent as in the mouse. The identification of regulatory CD4⁺CD25⁺ T cells has important implications for the study of tolerance in man, notably in the context of autoimmunity, transplantation, and cancer.