RUNX1T1 and acute myeloid leukemia: In contrast to the BM though, the relative number of AML-ETO+ LSK cells in the spleen was similar in aged and young recipients transplanted with AML-ETO+ hematopoietic cells, indicating that not systemic, but local niche/environment factors inside the BM are responsible for the age-associated higher level of expansion of myeloproliferation-initiating LSK cells in the BM of aged animals.