Another way of improving the outcome of therapy by increasing apoptotic cell death is associated with upregulation of expression of apoptosis inducing genes and downregulation of apoptosis-suppressing genes (81, 113, 114). Hematopoietic cytokines can also affect leukemic cell behavior by controlling cell differentiation. Different CSFs and interleukins such as IL-1 and IL-6 can control the abnormal growth of certain types of leukemic cells and suppress malignancy by inducing cell differentiation (reviewed in refs. 26-29). Like retinoic acid, which induces differentiation in certain types of myeloid leukemic cells and is effectively used in the clinic to treat such patients (75), differentiationinducing cytokines may also be an effective treatment for certain types of leukemias. The existence of the cytokine network has to be taken into account in the clinical use of cytokines (27).