IL-7R signaling is essential for Notch1-induced T-ALL pathogenesis. BM Lin⁻ c-kit⁺ HPCs isolated from wt or Il7r^−/− H2-Kb⁺ mice were transduced with lentiviral vectors encoding ICN1 and GFP and transplanted into H2-Kb⁻ immunodeficient mice. (A) CD4 and CD8 expression of electronically gated transduced (ICN1⁺) and nontransduced (ICN1⁻) H2-Kb⁺Il7r wt or Il7r^−/− donor cells engrafting the BM of transplanted mice at 4 weeks posttransplant. Results are representative of 1 of ≥18 mice per group (n = 3). Engraftment potential of ICN1-transduced (B) and total H2-Kb⁺ (C) donor cells. Data are percentages (mean ± standard error of the mean [SEM]) of donor cells recovered from the peripheral blood of ≥18 mice per group at 4 weeks posttransplant (n = 3). (D) Percentages of myeloid-lineage (CD11b⁺ or Gr1.1⁺), B-lineage (B220⁺), T-lineage (DP; CD4⁺CD8⁺ and/or CD8⁺CD4⁻) or Lin⁻ (CD11b⁻, Gr1.1⁻, B220⁻, CD4⁻, CD8⁻) cells derived from transduced (ICN1⁺) and nontransduced (ICN1⁻) donor cells engrafting the spleen of transplanted mice at 5 weeks posttransplant. Mean ± SEM values from ≥18 mice per group are shown (n = 3). (E) Kaplan-Meier survival curves of immunodeficient mice transplanted with wt or Il7r^−/− BM HPCs transduced with ICN1. (F) Percentages of ICN1⁺ transduced cells recovered at 5 weeks posttransplant from the indicated organs of immunodeficient mice transplanted with wt or Il7r^−/− BM HPCs. Mean ± SEM percentages of ≥14 mice per group are shown (n = 3). **P < .01, ***P < .001. ns, not significant.