AFF1 and leukemia: Although we focused our analysis on RUNX1, whose role in KMT2A-FP leukemias has been observed previously (Wilkinson et al. 2013; Prange et al. 2017), placing RUNX1 in the context of the KMT2A-AFF1 GRN allows us to capture complex aspects of the KMT2A-AFF1:RUNX1 regulatory axis.