MYELOID NEOPLASIA Evolution of acute myelogenous leukemia stem cell properties after treatment and progression

wasassessedby limitingdilutionanalyses. LSC populations were identified using fluorescent-labeled cell sorting and transplantation into immuno-deficient NOD/SCID/interleukin 2 receptor g chain null mice. The surface antigen expression profiles of pretherapy and postrelapse LSCs were determined for published LSC markers. We demonstrate a 9- to 90-fold increase in LSC frequency between diagnosis and relapse. LSC activity at relapse was identified in populations of leukemic blasts that did not demonstrate this activity before treatment and relapse. In addition, we describe genetic instability and exceptional phenotypic changes that accompany the evolution of these new LSC populations. This study is the first to characterize the evolution of LSCs in vivo after chemotherapy, identifying a dramatic change in the physiology of primitive AML cells when the disease progresses. Taken together, these findings provide a new frame of reference by which to evaluate candidate AML therapies in which both disease control and the induction of more advanced forms of disease should be considered. ( Blood . 2016;128(13):1671-1678) LSCs have been proposed, including CD123, 6,7 CD32, 8 CD33, 9 CD45RA, 10 CD47, 11 CD96, 12 CD99, 13 IL1RAP, 14 and TIM-3. 15 Recent studies have identi fi ed increasing intrapatient and interpatient heterogeneity of AML LSC populations. 16-19 A direct assessment of intrapatient evolution of LSCs that may occur during disease pathogenesis and/or treatment has not been reported. We investigated the frequency and surface antigen phenotypes of functionally de fi ned LSCs in paired primary human AML samples at diagnosis and in relapse. Surprisingly, we found that LSC frequencies and phenotypic diversity are much greater at relapse than before initial therapy. Our data indicate that current AML therapeutic regimens may promote dramatic changes in the LSC compartment. A better understanding of how these changes occur will aid in the development of novel therapeutics for patients with relapsed disease.