Runx1^lacZ/lacZ chimeras are more susceptible to developing T-lymphoblastic lymphoma than wild-type chimeras. (A) Kaplan-Meier survival curves (lymphoma-free) are shown for untreated Runx1^lacZ/lacZ (n = 6) and Runx1^lacZ/lacZ (n = 6) and wild-type (n = 6) chimeras treated with 100 mg/kg ENU. • indicates untreated Runx1^lacZ/lacZ chimeras; ▪, wild-type ES-cell chimeras treated with ENU; ▴, Runx1^lacZ/lacZ chimeras treated with ENU. (B) Hematoxylin and eosin (H&E) staining of thymus, bone marrow (BM), and liver from LZD nos. 2 through 5. Immunohistochemistry using an anti-CD3 antibody demonstrates that the malignant cells in the livers of these animals stained positively for CD3. (C) Flow cytometry of thymocytes from LZD no. 2 and LZD no. 4 using antibodies against CD4 and CD8 demonstrates that the majority of cells have an abnormal CD4⁺/CD8⁺ phenotype. WT indicates wild type. Numbers in each quadrant indicate the percentage of total thymocytes in that quadrant.