CD4 and systemic lupus erythematosus: Therefore, such an acquired phenotype may not correlate with functional CD4+CD25+CD127low Treg cells and caution must be exercised when evaluating systemic IL-2 drug treatment as an attempt to stimulate and/or increase CD4+CD25+CD127low Tregs in patients suffering from SLE and other autoimmune diseases, since the correlation of in vivo expansion of CD4+CD25+CD127low Treg cells in response to low-dose IL-2 in SLE patients with a clinical response in open-label studies did not translate into clinical efficacy in randomized controlled trials (37).