Cell populations in transgenic mice before leukemia onset. (A) Spleen and bone marrow cells from 2-month-old transgenic mice (n = 6 to 7 for each genotype) were analyzed by flow cytometry for pro-B (B220+CD43+IgM–), pre-B (B220+CD43–IgM–), immature B (B220+CD43–IgM+), and mature B (splenic IgMlowIgDhi) cells. Differences between groups were not significant. (B) Spleen cells from 2-month-old BRAFWT or BRAFVE TCL1 transgenic mice (n = 6 per genotype) were analyzed by flow cytometry for B-, T-, and myeloid cell populations. BRAFVE×TCL1 mice showed a minor but significant increase in myeloid (CD11b+) cells before the onset of leukemia and trends toward increased B (B220+) and decreased T (CD3+) cells. The horizontal bars represent the median.