Despite sharing similar properties with IL-2 (3) such as activation of NK, NKT, γδ T cells and cytotoxic CD8+ T lymphocytes, IL-15 bears advantages over IL-2 in stimulation and maintenance memory CD8+ T cell response (4), lack of activation-induced cell death (5), T regulatory cell expansion or inducing capillary leak syndrome (6). The gene discussed is CD8A; the disease is capillary leak syndrome.