[6], [7] IL-15 is an important mediator of growth, and survival of the malignant cells in hematopoietic malignancies and solid tumors. [6], [8], [9] In fact, overexpression of IL-15 in transgenic mice is sufficient to cause CD8 leukemia and T-LGL or NKT leukemia. [10], [11] While IL-15 over-expression promotes leukemia/lymphoma, it is less well understood if IL-15 is a necessary prerequisite for cancer development. The gene discussed is IL15; the disease is leukemia.