We found that the combination of Hoxa9 and hSYK significantly increased the aggressiveness of the leukemias compared with Hoxa9 alone (median of 38.5 versus 103.5 days; p < 0.001), with a median survival remarkably similar to that of Hoxa9/Meis1 (39 days; Figures 6B and S5P). Here, MEIS1 is linked to leukemia.