Human CD4+ regulatory T cells express lower levels of the IL-7 receptor alpha chain (CD127), allowing consistent identification and sorting of live cells

Although quantitative identification and viable enrichment of natural regulatory T cells (T-regs) in humans are problematic, such steps would greatly facilitate the analysis of these cells in disease states. In an attempt to identify markers that are sensitive and specific for human T-regs, we analyzed the expression of fourteen intracellular and cell surface markers on human CD4⁺ cells. Many markers were partially selective for CD25^hi T-regs, but consistent and specific discrimination of functional T-regs was only made possible by focus on CD127, the alpha chain of the IL-7 receptor. Although most CD4⁺ human T cells express CD127, T-regs exhibiting suppressive activity in vitro display distinctly lower surface expression of this marker, irrespective of their level of CD25 expression. Sorted cells with the surface phenotype CD4⁺CD25⁺CD127^low had higher levels of intracellular FOXP3 and CTLA-4 and, as determined by functional assays, were suppressive, hypoproliferative, and poorly responsive to TCR signaling. The CD4⁺CD25⁺CD127^low phenotype was also found to be characteristic of T-regs found in mice and in rhesus macaques. This surface phenotype should allow for quantitative studies of regulatory T cells in disease states as well as for enrichment of live regulatory T cells for functional analyses and/or expansion in vitro.