MA9 leukemogenesis in vivo is sensitive to inhibition of Bcl-2 proteins. MA9 leukemia burden was dramatically reduced in xenografted NSS mice treated with ABT-737 (N = 5) versus vehicle control (N = 4; P < .005). Bone marrow was sampled at day 0, day 10, and end of treatment (day 22) and engraftment measured by FACS.