Il2 deletion in the CD4+ T-cell compartment resulted in characteristic IL-2 Deficiency Syndrome24–26 originally described in Il2KO mice and characterized by severe anemia (Fig. 9a), splenomegaly (Fig. 9b), uncontrolled expansion of splenic T cells associated with reduction of Treg cells and loss of B cells. The gene discussed is IL2; the disease is anemia.