The length of in vitro culture influences leukemia development in vivo. (A) Survival curves for mice transplanted with gene-edited MLLr cells cultured for different times in vitro prior to transplant. (B) Flow cytometry analysis of BM cells in leukemic mice for myeloid (CD33) and lymphoid (CD19) lineage markers. (C) Flow cytometry analysis (left panel) of tissues from a representative leukemic mouse and their corresponding MLL-AF9 and AF9-MLL junctions (right panel), as determined by Sanger sequencing of DNA isolated from the indicated respective tissues. *P < .0358, **P < .0001, ***P < .0440, log-rank test.