**7. Abbreviatons**

PcG, Polycomb Group, PRC1, Polycomb repressive complex 1, PRC2, polycomb repressive complex 2.

### **8. References**


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PcG, Polycomb Group, PRC1, Polycomb repressive complex 1, PRC2, polycomb repressive

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**12** 

*Brazil* 

**Hematopoietic Stem Cell in Acute Myeloid** 

Hematopoietic stem cells (HSCs) are multipotent stem cells defined by their ability to selfrenewal, differentiation and maintenance of all blood cell types in the hematological system during the entire lifetime of the organism. This physiological process, called hematopoiesis, is controlled by several complex interactions between genetic processes in blood progenitor cells and bone marrow microenvironment. Hemostasis is maintained by a delicate balance between processes such as self-renewal, proliferation and differentiation versus apoptosis and cell-cycle arrest in HSCs. Over the last two decades, several studies have been made to understand possible mechanisms of cell malignancy and tumor growth, both in solid and hematological cancers. Leukemias are hematological malignancies that arise from cancer stem cells (CSCs). Neoplastic transformation of hematopoietic stem or progenitor cells occurs by unbalanced critical mechanisms. Blood cancers, as acute myeloid leukemia (AML), are sustained by leukemic stem cells (LSCs) which, like normal HSCs, present a range of biological characteristics that enable their long-term survival. AML is a well studied hematological cancer type characterized by an accumulation of clonal myeloid progenitor cells that do not differentiate normally. However, there is still no consensus about the mechanisms by which the HSCs transformation occurs. In this chapter, the hematopoietic stem cells and leukemic stem cells will be focused on leukemia development,

Hematopoietic stem cells are a well characterized stem cell type which has been used in bone marrow transplantation for treatment of hematological malignancies as well as nonmalignant disorders (Warner et al, 2004). In fact, bone marrow (BM) has been, for many years, transplanted as an unfractionated cell pool, until researchers discovered which cellular components were responsible for the engraftment of the donor hematopoietic and

HSCs present self-renewal potential and differentiation capacity into blood lineages. The self-renewal concept means that when stem cells divide, 50% of the daughter cells, on average, is committed with a cell lineage; the remaining 50% do not differentiate; therefore

**1. Introduction** 

mainly in AML.

**2. Hematopoietic stem cells** 

immune systems in marrow-ablated patients.

**Leukemia Development** 

*University of Sao Paulo School of Medicine* 

Sérgio Paulo Bydlowski and Felipe de Lara Janz

*Laboratory of Genetics and Molecular Hematology, São Paulo, SP,* 

