Most likely, “infant ALL” - especially cells with t(4;11)/KMT2A::AFF1 translocations - derives from rapidly growing proB fetal liver cells (CD10-, CD19+, CD34+), while all other disease subgroups derive from bone marrow hematopoietic stem/precursor cells [30, 31]. This evidence concerns the gene AFF1 and acute lymphoblastic leukemia.