A transient population of Csf2rb⁺ cells is seen in the peripheral blood after Cbfb-MYH11 induction. (A) Line graphs showing percentage (%) of Csf2rb⁺ cells in the peripheral blood at the indicated number of weeks after pI:pC treatment in 3 representative mice. The line marked with circles represents a wild-type mouse after pI:pC treatment. The line marked with triangles represents a conditional Cbfb-MYH11 knockin mouse after pI:pC treatment that did not develop leukemia within the observed time period (7 weeks). The line marked with diamonds represents a conditional Cbfb-MYH11 knockin mouse after pI:pC treatment that spontaneously developed AML (without ENU). (B) Percentage of Csf2rb⁺ cells in a larger cohort of mice at the indicated number of weeks after pI:pC treatments. *Statistically significant difference between Cbfb^+/56M, Mx1-Cre and control mice (P < .02). Wright-Giemsa staining of sorted Csf2rb⁺ peripheral blood cells from (C) a preleukemic Cbfb^+/56M, Mx1-Cre mouse 2 weeks after Cbfb-MYH11 induction and (D) a leukemic Cbfb^+/56M, Mx1-Cre mouse. Magnification, 1000×.