Low-dose IL-2 therapy expands human regulatory T cell populations

Interleukin-2 (IL-2) promotes both effector T and regulatory T (T_Reg) cell responses, but it is believed that T_Reg cells may be more sensitive to IL-2. Two recent studies found that low-dose IL-2 therapy preferentially expands T_Reg cell populations in humans. Koreth et al. administered low-dose IL-2 to 29 patients with chronic graft-versus-host disease (GVHD). This increased T_Reg cell numbers in all patients without altering effector T cell numbers. Around half of the subjects showed clinical improvement; some patients even showed an improvement in GVHD manifestations that had been considered irreversible. Importantly, IL-2 therapy did not impair other immune functions. Saadoun et al. studied low-dose IL-2 therapy in 10 patients with autoimmune vasculitis induced by hepatitis C virus infection. All patients showed increased proportions of functional T_Reg cells, with 9 patients showing clinical improvement. Notably, the authors did not report any adverse effects of IL-2 therapy. Although not all patients showed clinical improvement in the studies, these results are promising.