MMP-9 secreted by leukemic cells expressing BCR-ABL and Hes1 promoted the release of sKitL from stromal cells. (A-B) Levels of MMP-9 (A) or sKitL (B) in culture supernatants of WT or MMP-9–deficient CMPs expressing BCR-ABL and Hes1 cultured for 24 hours were measured by ELISA. (C-D) Levels of MMP-9 (C) or sKitL (D) in culture supernatants of WT or MMP-9–deficient CMPs expressing BCR-ABL and Hes1 that had been co-cultured with MS-5 stromal cells for 24 hours were measured by ELISA. (E-F) Plasma levels of MMP-9 (E) or sKitL (F) at the indicated days in the recipient mice transplanted with WT or MMP-9–deficient CMPs expressing BCR-ABL and Hes1 or in mice without transplantation were measured by ELISA. (G) Growth of WT CMPs expressing BCR-ABL and Hes1 in the presence or absence of 50 ng/mL SCF. (H) Growth of WT or MMP-9–deficient CMPs expressing BCR-ABL and Hes1 cultured with or without MS-5 cells without SCF. (G-H) The numbers of cells were determined by trypan blue staining. (G) 2 × 10⁵ cells per well were seeded into a 6-well plate. (H) 1 × 10⁵ cells per well were seeded into a 6-well plate. (A-H) All data points correspond to the mean and the SD of 3 independent experiments. (E-H) Statistically significant differences are shown: *P < .05, **P < .01.