3q21q26::Gata2^+/−leukemia cells expand advantageously compared with the 3q21q26 leukemia cells. (A) Schema for the transplantation analysis. Either 5 × 10⁴ B220⁺Gr1^–c-Kit⁺ cells from leukemic 3q21q26 mice (CD45.1/CD45.2 heterozygotes), and/or from 3q21q26::Gata2^+/− (CD45.1 homozygous) mice, or a mixture of 2.5 × 10⁴ cells each from those same populations were independently transplanted into 3 sets of sublethally irradiated CD45.2 WT mice. (B) Kaplan-Meier survival curves of mice that received B220⁺Gr1^–c-Kit⁺ cells from leukemic 3q21q26 and 3q21q26::Gata2^+/− mice. In Experiment 1 (left panel), the B220⁺Gr1^–c-Kit⁺ cells from leukemic 3q21q26 Type II mice (n = 4; median, 66.5 days), 3q21q26::Gata2^+/− mice Type I (n = 4; median, 28.0 days), and the mixture (n = 4; median, 28.0 days) were observed for the given days survived. In Experiment 2 (right panel), B220⁺Gr1^–c-Kit⁺ cells from leukemic 3q21q26 Type I mice (n = 4; median, 49.0 days), 3q21q26::Gata2^+/− Type I mice (n = 4; median, 48.5 days), and the mixture (n = 4; median, 42.0 days) were observed for survival. (C) Flow cytometric patterns of CD45.1 and CD45.2 in the bone marrows of WT mice receiving B220⁺Gr1^–c-Kit⁺ cells from 3q21q26 or 3q21q26::Gata2^+/− mice alone or from the mixture. **P < .01. n.s., not significant.