In vivo pharmacologic inhibition of the Bcl-2 family members leads to decreased human LSC regenerative and self-renewal function. (A) Experimental strategy used to examine the effects of obatoclax on primitive human leukemic cell phenotype and SL-IC self-renewal capacity. (B) Representative examples of flow cytometry analyses used to assess the effects of obatoclax on human leukemic engraftment relative to vehicle control. The BM of recipient mice that received a transplant with human SL-IC and subsequently administered obatoclax or vehicle control was analyzed for total (CD45 expression), myeloid (CD33 expression), and primitive (CD34 expression) human leukemic engraftment. Percentages of 70% and 45% represent the frequency of cells gated for human component in chimeric mice transplanted with pretreated and treated mice, respectively. (C) Analysis of the effect of obatoclax on human SL-IC capacity. The average frequency of human leukemic engraftment (CD45⁺ cells) in the BM of primary recipient mice administered obatoclax is expressed relative to mice administered vehicle control. Error bars represent the mean ± SEM of 3 independent experiments, each with 3 mice per group. (D) Analysis of the effect of obatoclax on primitive (CD34⁺) human leukemic engraftment. The average frequency of CD34⁺ cells within the human leukemic graft (gated CD45⁺ cells) in the BM of primary recipient mice administered obatoclax is expressed relative to mice administered vehicle control. Error bars represent the mean ± SEM of 3 independent experiments, each with 3 mice per group. **P < .01. (E) Analysis of the effect of obatoclax on human SL-IC self-renewal capacity. The average frequency of human leukemic engraftment (CD45⁺ cells) in the BM of secondary recipient mice that received a transplant with human leukemia-engrafted BM isolated from primary recipient mice administered obatoclax is expressed relative to vehicle control. Error bars represent the mean ± SEM of 3 independent experiments, each with 3 mice per group. *P < .05.