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

AlthoughquantitativeidentificationandviableenrichmentofnaturalregulatoryTcells(T-regs)inhumansareproblematic,suchsteps 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 discriminationoffunctional T-regswas only made possible by focus on CD127, the alpha chain of the IL-7 receptor. Although most CD4 + human Tcells 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 foundtobecharacteristicofT-regsfoundinmiceandinrhesusmacaques.Thissurfacephenotypeshouldallowforquantitativestudiesof