The ordered acquisition of Class II and Class I mutations directs formation of human t(8;21) acute myelogenous leukemia stem cell

The cellular properties of leukemia stem cells (LSCs) are achieved at least through Class I and Class II mutations that generate signals for enhanced proliferation and impaired differentiation, respectively. Here we show that in t(8;21) acute myelogenous leukemia (AML), hematopoietic stem cells (HSCs) transform into LSCs via definitively-ordered acquisition of Class II (AML1/ETO) and then Class I (c-KIT mutant) abnormalities. Six t(8;21) AML patients with c-KIT mutants maintaining>3years of complete remission were analyzed. At diagnosis, all single LSCs had both AML1/ETO and c-KIT mutations. However, in remission, 16 out of 1,728 CD34⁺CD38^- HSCs and 89 out of 7,187 single HSC-derived myeloerythroid colonies from these patients had AML1/ETO, whose breakpoints were identical to those found in LSCs. These cells had wild-type c-KIT, which expressed AML1/ETO at a low level, and could differentiate into mature blood cells, suggesting that they may be the persistent preleukemic stem cells. Microarray analysis suggested that mutated c-KIT signaling provides LSCs with enhanced survival and proliferation. Thus, in t(8;21) AML, the acquisition of AML1/ETO is not sufficient, and the subsequent upregulation of AML1/ETO and the additional c-KIT mutant signaling are critical steps for transformation into LSCs.