To address whether IL4-induced apoptosis is mediated by p53, a well-known regulator of apoptosis,20 we used murine Tp53−/−MLL-AF9 leukemia cells, previously generated by us.13 We found that similar to Tp53+/+ AML cells (Figure 2c), IL4 forced Tp53−/− AML cells into apoptosis resulting in reduced cell numbers upon culture (Figures 2e and f). Here, TP53 is linked to leukemia.