Low-dose IL-2 preferentially stimulates proliferation, function, and survival of Treg; low-dose IL-2 administration to patients has been shown expands Treg and ameliorates chronic GVHD in a proportion of patients (161, 162). Efavakeukin-α, IL-2 mutein, is currently tested in a clinical trial. The gene discussed is IL2; the disease is chronic graft versus host disease.