Abstract
Within the past years there have been substantial changes to our understanding of haematopoiesis and cells that initiate and sustain leukemia. Recent studies have revealed that developing haematopoietic stem and progenitor cells are much more heterogeneous and versatile than has been previously thought. This versatility includes cells using more than one route to a fate and cells having progressed some way towards a cell type retaining other lineage options as clandestine. These notions impact substantially on our understanding of the origin and nature of leukemia. An important question is whether leukemia stem cells are as versatile as their cell of origin as an abundance of cells belonging to a lineage is often a feature of overt leukemia. In this regard, we examine the coming of age of the "leukemia stem cell" theory and the notion that leukemia, like normal haematopoiesis, is a hierarchically organized tissue. We examine evidence to support the notion that whilst cells that initiate leukemia have multi-lineage potential, leukemia stem cells are reprogrammed by further oncogenic insults to restrict their lineage decision-making. Accordingly, evolution of a sub-clone of lineage-restricted malignant cells is a key feature of overt leukemia.
Highlights
An important question regarding stem and progenitor cells choosing a developmental route is whether the routes these cells follow to a mature cell type are invariant or versatile
Treatment of zebrafish embryos with a RARγ-specific agonist adversely affected the development and growth of tissues that form from neural crest and lateral plate mesodermal stem and progenitor cells that express RARγ. These studies revealed that RARγ, which can play a role in cell reprogramming, has to be inactive at the stem/progenitor stage of development for these cells to make an appropriate decision to differentiate along a pathway [41]
haematopoietic stem cell (HSC) carrying these mutations can produce a number of myeloid or lymphoid progenitors that have identical abnormalities and these progenitors can be the final target for the transformation of LOCs into leukemia stem cell” (LSC) in acute leukemia [71]
Summary
An important question regarding stem and progenitor cells choosing a developmental route is whether the routes these cells follow to a mature cell type are invariant or versatile. In the classical view of the initiation and progression of leukemia, an initiating www.impactjournals.com/oncotarget genetic alteration takes place that is required for the immortalization of a committed/differentiated target cell (Figure 5B).
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