Efficient inactivation of Dicer1 rescues mice from early stage T-ALL. (A) Lin⁻ BM cells from CD45.2⁺ donors (Dicer1^lox/lox or Dicer1^{lox/lox Mx1-Cre}) were retrovirally transduced with hN1ICD-NGFR or NGFR alone and transplanted into CD45.1⁺ congenic hosts. Once NGFR⁺ cells were detected in PBLs (at day 38 p.tr.), Mx1-Cre was activated using p-I:C. A second round of 3 p-I:C injections was initiated at day 60 p.tr. in order to activate Mx1-Cre in residual Dicer1^lox/lox T-ALL cells in Dicer1^∆Mx1-Cre BM chimeras. (B) Kaplan-Meier survival plot of chimeric animals pooled from 2 independent experiments as outlined in panel A. Depicted are 3 experimental groups: (1) Dicer1^lox/lox transduced with NGFR control RV particles, Dicer1^lox/loxNGFR; (2) Dicer1^lox/lox transduced with hNICD-NGFR RV particles, Dicer1^lox/loxhNICD-NGFR; and (3) Dicer1^{lox/lox Mx1-Cre} transduced with hNICD-NGFR RV particles, Dicer1^ΔMx1-Cre hNICD-NGFR . The dashed line indicates MST: red= 52 days, green = 82.5 days. (C) Expansion of peripheral T-ALL cells measured by the percentage of NGFR⁺ cells in total PBLs from panel B. (D) Representative FACS plots of NGFR⁺ PBLs of Dicer1^lox/lox or Dicer1^{lox/lox Mx1-Cre} at day 38 p.tr. (upper panel) and at day 67 p.tr. Dicer1^lox/lox and day 75 p.tr. Dicer1^ΔMx1-Cre (lower panel). The CD4⁺ vs CD8⁺ profile is shown gated on NGFR⁺ cells based on the positive fraction in the histograms. (E) Dicer1 deletion PCR on DNA extracted from total splenocytes of a representative Dicer1^ΔMx1-Cre BM chimeric animal with incomplete Dicer1 deletion at day 75 p.tr. (left) and on sorted (CD45.2⁺ NGFR⁺) T-ALL cells from the same spleen (right).