Normal Hematopoietic Stem Cells within the AML Bone Marrow Have a Distinct and Higher ALDH Activity Level than Co-Existing Leukemic Stem Cells

Abstract

Persistence of leukemic stem cells (LSC) after chemotherapy is thought to be responsible for relapse and prevents the curative treatment of acute myeloid leukemia (AML) patients. LSC and normal hematopoietic stem cells (HSC) share many characteristics and co-exist in the bone marrow of AML patients. For the development of successful LSC-targeted therapy, enabling eradication of LSC while sparing HSC, the identification of differences between LSC and HSC residing within the AML bone marrow is crucial. For identification of these LSC targets, as well as for AML LSC characterization, discrimination between LSC and HSC within the AML bone marrow is imperative. Here we show that normal CD34+CD38– HSC present in AML bone marrow, identified by their lack of aberrant immunophenotypic and molecular marker expression and low scatter properties, are a distinct sub-population of cells with high ALDH activity (ALDHbright). The ALDHbright compartment contains, besides normal HSC, more differentiated, normal CD34+CD38+ progenitors. Furthermore, we show that in CD34-negative AML, containing solely normal CD34+ cells, LSC are CD34– and ALDHlow. In CD34-positive AML, LSC are also ALDHlow but can be either CD34+ or CD34–. In conclusion, although malignant AML blasts have varying ALDH activity, a common feature of all AML cases is that LSC have lower ALDH activity than the CD34+CD38– HSC that co-exist with these LSC in the AML bone marrow. Our findings form the basis for combined functionally and immunophenotypically based identification and purification of LSC and HSC within the AML bone marrow, aiming at development of highly specific anti-LSC therapy.

Attenuation of microRNA-126 Expression That Drives CD34+38− Stem/Progenitor Cells in Acute Myeloid Leukemia Leads to Tumor Eradication

“…These markers include CLL1, CD123, CD47, CD96, Tim3, and lineage markers such as CD56 and CD7 (11)(12)(13)(14)(15)(16). Moreover, we and others identified that in general leukemic CD34 þ CD38 À cells have lower aldehyde dehydrogenase (ALDH) activity than HSCs coexisting in the AML BM (17,18). Importantly, ALDH activity can reliably distinguish leukemic CD34 þ CD38 À cells, capable of leukemic engraftment, from CD34 þ CD38 À HSCs, capable of multilineage engraftment (17,18).…”

“…Moreover, we and others identified that in general leukemic CD34 þ CD38 À cells have lower aldehyde dehydrogenase (ALDH) activity than HSCs coexisting in the AML BM (17,18). Importantly, ALDH activity can reliably distinguish leukemic CD34 þ CD38 À cells, capable of leukemic engraftment, from CD34 þ CD38 À HSCs, capable of multilineage engraftment (17,18). miRNAs are small, noncoding RNAs that control gene expression by repressing translation or by promoting degradation of target mRNAs (19).…”

Leukemic stem cells: identification and clinical application

“…In these cases the commonly small CD34+ (<1%) blast population does not contain leukemic cells [18,20,21]. By definition, these CD34− patients lack CD34+/CD38− or CD34+/CD38+ leukemic populations; however, a potential LSC population should be found within the remaining CD34− fraction.…”

“…In normal BM CD34+/CD38− HSC display high levels ALDH activity (ALDH high ) [29]. In both normal BM and in the majority of AML BM cells, the CD34+/CD38−/ALDH high population is considered to contain only HSC [21,29,30]. In contrast to normal BM, in AML a second population can be discriminated with cells having intermediate ALDH expression [29].…”

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for “prime time”?

“…An experienced laboratory and an adequate sampling 26 optimize assay sensitivity, but from published studies about onethird of younger patients without detectable MFC-MRD at predictive time points will relapse; these are the false negatives of the assay. 1 myeloblasts (defined by gating using 32 Recent data suggest that xenograft LSC frequency of different AML genetic subclones from presentation samples may not necessarily predict their emergence at relapse, 23 underlining the need to evaluate the clinical relevance of any potential MFC LSC residual disease assay.…”