Recently, engineered Treg-selective human IL-2 was developed in humanized mice during xenogeneic GVHD (64), and Efavaleukin Alfa (AMG-592), a human IL-2 mutant designed to have greater Treg selectivity and longer half-life compared with recombinant IL-2, is now under a clinical trial for patients with SR-cGVHD (NCT03422627). The gene discussed is IL2; the disease is graft versus host disease.