First results from an phase I/II trial (PRO-IMMUN) demonstrated that one 5-day course of low-dose IL-2 therapy with daily injections of 1.5 million IU was capable to selectively increase CD25 expression in CD4+Foxp3+CD127lo Treg and to promote the efficient and selective expansion of the CD4+FoxP3+CD127lo Treg population in five patients with active SLE (25). This evidence concerns the gene IL2 and systemic lupus erythematosus.