Replacement of the FLT3^wt/wt in FLT3^−/ITD BM postponed the development of fatal MPN in recipient mice. (A) Structure of the dual-promoter wtFLT3 lentiviral vector used in these studies (i) and expression of FLT3 in GFP⁺ transduced cells (ii). Transcripts from lentivirus with single or dual internal promoters are denoted with arrows. R and U5 indicates the repeat and U5 region, respectively, in the viral LTR; WPRE, woodchuck post-transcriptional regulatory element; EF1α, human EF1α promoter/enhancer; Ubc, human ubiquitin promoter; and GFP, enhanced green fluorescent protein. (B) Methylcellulose-based in vitro colony-forming assay was performed on GFP⁺ lentiviral-transduced lineage-depleted BM from 2-month-old mice. (C) Kaplan-Meier survival curve for recipients of viral-transduced unsorted (i) and sorted (ii) FLT3^−/ITD Lin⁻ cells. (D) Flow cytometric analysis of BM from recipients of unselected transduced BM. Numbers indicate the percentages of cells in whole BM.