CD127low/- and FoxP3+ Expression Levels Characterize Different Regulatory T-Cell Populations in Human Peripheral Blood

It has recently been suggested that a lack of CD127 expression can be used to identify human CD4+ regulatory T cells (Tregs), especially when combined with CD25. Therefore, we analyzed CD4+CD25+CD127low/- cells and compared their frequency and expression pattern with those of FoxP3+ Tregs using multiparameter flow cytometry analysis. We obtained human peripheral blood cells from 20 normal healthy donors and determined the number of CD25+CD127low/- cells as a percentage of CD4+ T cells in the same panel used for CD4+CD25+FoxP3+ cells. In contrast to CD4+CD25+FoxP3+ cells, gating of a clear CD4+CD25+CD127low/- population was difficult. Moreover, we demonstrated that there was a high percentage (34.0±15.1%) of CD127low/- cells that did not express FoxP3 and, conversely, that there was a high percentage (30.3±7.4%) of CD127+ cells that expressed FoxP3, suggesting that these markers did not represent the same population of Tregs. These data were also confirmed in blood samples from patients with systemic scleroderma. Thus, isolation of pure Treg populations for in vitro functional studies is a challenge, explaining the varying results by different groups in clinical studies. The data from this study have important implications for carrying out a quantitative analysis of Tregs in human samples.