KMT2A and leukemia: We then measured the levels of ctDNA (copies/μL) and observed a significant correlation with leukemia burden (% huCD45+) in mice engrafted with MLL-1, MLL-2, and MLL-7 PDXs (r = 0.75, 0.88, 0.85 p < 0.0001, respectively) (Figure 2B–D).