In fact, the cytokines up-regulated in co-cultures most probably enhance leukemic clone formation by regulating cellular proliferation and apoptosis, since specific cytokines, such as IL-2, IL-4, IL-10, IL-15, and TNF-alpha [25], can influence the survival of B-CLL cells in vivo. The gene discussed is IL4; the disease is B-cell chronic lymphocytic leukemia.