Ikaros is a zinc finger transcriptional regulator encoded by the Ikzf1 gene.Ikaros displays crucial functions in the hematopoietic system and its loss of function has been linked to the development of lymphoid leukemia.In particular,Ikaros has been found in recent years to be a major tumor suppressor involved in human B-cell acute lymphoblastic leukemia.Its role in T-cell leukemia,however,has been more controversial.While Ikaros deficiency appears to be very frequent in murine T-cell leukemias,loss of Ikaros appears to be rare in human T-cell acute lymphoblastic leukemia (T-ALL).We review here the evidence linking Ikaros to T-ALL in mouse and human systems.