PML/RARA extinction triggers APL differentiation in vivo. Bone marrow APL blasts were infected with a GFP-expressing lentivirus encoding a scrambled shRNA sequence (Ctrl) or an shRNA sequence directed against human PML and injected in secondary recipients. Inoculated animals were analyzed 21 days after engraftment (6 mice, 2 independent experiments) to determine the proportion of GFP-positive cells in the marrow (A), PML/RARA or GFP immunofluorescence (bottom bar, 10 µm; arrow points to differentiated GFP-positive cells with PML/RARA extinction) (B), and fluorescence-activated cell sorter analysis of GFP-positive cells (C). (D) Gene expression analysis 6 or 12 hours after RA (blue) or As₂O₃ (red) treatment in human APL NB4 cell line (top row) or of APL mice (bottom row). See supplemental Figure 2 for representative data. (E) χ² test P values (median P value for the different thresholds tested: N = 100-1200) for association of the upregulated and downregulated genes. Sample 935 refers to murine APLs; AR10 and AR100 indicate the doses of RA administered.