Development of T-ALL in mice transplanted with Dnmt3a-KO HSCs. (A) Thymus weights of mice transplanted with WT HSCs killed as age-matched controls while healthy, and 4 mice transplanted with Dnmt3a-KO HSCs that presented with enlarged thymuses on necropsy. Error bars represent mean ± SEM. (B) WBC count over time for 1 mouse receiving Dnmt3a-KO HSCs and 3 representative WT mice. Error bars represent mean ± SEM. (C) Bone marrow touch preps stained with Wright-Geimsa from a representative mouse transplanted with WT HSCs and from a mouse with T-ALL. Bars represent 20 μm. (D) Fluorescence-activated cell sorter analysis of the same Dnmt3a-KO recipient and a representative WT, showing (top row) that CD45.2 (donor) cells make up nearly all of the bone marrow cells, and (bottom row) myeloid (My), B cells (indicated with letter B), and T cells (T); parent gate is live cells. (E) Further immunophenotyping of these mice, bone marrow stained with CD4 and CD8; parent gate is live; CD45.2⁺. (F) Chromatogram traces showing Notch1 mutations identified in 2 T-ALL mice in exon 27. The variant base is listed below the sequence in red, and corresponding amino acid changes are indicated. **P < .001.