The first larger clinical trial in Europe started in march 2014 and was a single-center, uncontrolled, dose-adaption, phase I/IIa trial (PRO-IMMUN) with the primary aim to investigate the safety, tolerability and biological efficacy of low-dose IL-2 therapy in 12 patients with active SLE who had refractory disease activity under conventional therapy (58). Here, IL2 is linked to systemic lupus erythematosus.