Not only can this molecule inhibit cytokine-induced STAT5 phosphorylation on T and NK cells but it also inhibits IL-2 or IL-15-induced cytolytic activity of NK cellsin vitro, prolongs survival in a mouse model of graft-versus-host disease, and inhibits the proliferation of cells from patients with the chronic/smoldering form of human T-cell lymphotropic virus-I (HTLV-I)-induced adult T cell leukemia69. The gene discussed is IL2; the disease is graft versus host disease.