In this issue of the Journal, the findings of two case series suggest that in vivo treatment with interleukin-2 can suppress immune-mediated diseases. In one study, Koreth et al.¹ found that low-dose interleukin-2 was associated with reversal of glucocorticoid-refractory chronic graft-versus-host disease (GVHD) in patients who had undergone allogeneic hematopoietic stem-cell transplantation (HSCT) for the treatment of lymphomas and leukemias. The control of chronic GVHD was not accompanied by the relapse of cancer in any patient.¹ In a second small case series, Saadoun et al.² found that treatment of patients with hepatitis C virus (HCV)–related vasculitis with low-dose interleukin-2 led . . .