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

Abstract

• Using AML as a model, we investigated the effect of treatment and disease evolution on functionally defined cancer stem cell populations.• We demonstrate large-scale changes in LSC frequency and phenotype after relapse, best described using highdimensional space analyses.Most cancers evolve over time as patients initially responsive to therapy acquire resistance to the same drugs at relapse. Cancer stem cells have been postulated to represent a therapy-refractory reservoir for relapse, but formal proof of this model is lacking. We prospectively characterized leukemia stem cell populations (LSCs) from a well-defined cohort of patients with acute myelogenous leukemia (AML) at diagnosis and relapse to assess the effect of the disease course on these critical populations. Leukemic samples were collected from patients with newly diagnosed AML before therapy and after relapse, and LSC frequency was assessed by limiting dilution analyses. LSC populations were identified using fluorescent-labeled cell sorting and transplantation into immunodeficient 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

The cell of origin and the leukemia stem cell in acute myeloid leukemia

“…Thus, studies have shown that LSCs can be found in subpopulations other than the CD34+/CD38-cells and that these LSC containing subpopulations have rapidly cycling cells. 52 It could also be shown that the LSC frequency can vary by almost three orders of magnitude between different leukemias, ranging from 1 in 10 000 to less than 1 in 5 million. 27,30 LSC frequencies in human AML can only be measured using limiting dilution assays in immunodeficient mice (see above for the limitations of these assays).…”

Leukemic stem cells: identification and clinical application

“…Recently it was shown that the constitution of AML at relapse may differ from diagnosis due to clonal changes including clonal evolution, clonal regression and clonal selection, with possible changes on immunophenotypic [32,33], cytogenetic [34], genetic [34,35] and epigenetic [35] level. Detailed whole genome sequencing studies, analyzing paired diagnosis-relapse samples, showed that at time of diagnosis, patients could present with a wide array of small subclones of which some remained in relapse [36]: indicative for clonal selection under therapy pressure.…”

A novel approach for the identification of efficient combination therapies in primary human acute myeloid leukemia specimens

“…7, 8, 9, 10, 11, 12 Despite this great leap forward in the understanding of the cellular biology of the disease 20 years ago, culture methods able to maintain LSC activity of human primary samples in vitro were only developed recently, eventually enabling relevant cell-based interrogation of the disease. 13 …”