AFF1 and leukemia: To test whether CRISPRMLL-AF4+ cells could generate leukemia in vivo, human FL CD34+ cells (13 pcw, n = 4; donors 1, 2, 3, and 6) were edited as before and transplanted into sublethally irradiated NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice (CRISPRMLL-AF4+, n = 3: donors 1 and 2; control, n = 5: donors 1, 2, 3, and 6).