Figure 4A demonstrates a dose–dependent increase in caspase-3 activation following treatment of APL cells with increasing concentrations of Ara-C in the absence of M2-BMSCs. In contrast, co-culture of APL cells with M2-BMSCs resulted in a significant reduction in caspase-3 activation in the presence of Ara-C. Similarly, M2-BM SN had a potent inhibitory effect on Ara-C induced PARP cleavage in the APL cells (Figure 4B). This evidence concerns the gene CASP3 and acute promyelocytic leukemia.