Biomedical Engineering Reference
In-Depth Information
Chapter 9
Stem Cell Sources, Harvesting,
and Clinical Use
In theory, there is no difference between theory
and practice. But in practice, there is.
- Yogi Berra
Hematopoiesis is an eventful and multifactorial continuous process in which a
variety of blood cells are produced through proliferation and differentiation from a
minor quantity of stem cells (SCs) [
1
]. A complex network of interactive matters
and factors accomplishes the toti/pluri/multipotent SC survival, maturation, and
multiplication. Namely, differentiation and proliferation of SCs in the bone marrow
(BM) are regulated by the extracellular matrix and microenvironment provided by
stromal cells [
1
] . These cells—including macrophages, fi broblasts, dendritic,
endothelial, and other cells—stimulate hematopoietic SCs by producing growth
factors like Flt3-ligand, stem cell factor or c-kit-ligand, various interleukins, granu-
locyte-macrophage colony-stimulating factor (GM-CSF), and granulocyte colony-
stimulating factor (G-CSF). Other cytokines secreted by stromal cells regulate the
adhesion molecules positioned on SCs, allowing them to remain in the BM or
migrate to an area where the respective cell type is needed [
1-
4
] . Thus, hematopoi-
etic SCs could be defined as cells capable for self-renewal with high proliferative
capacity and extensive potential to differentiate into all blood cells or numerous
somatic cell types (the so-called SC plasticity due to “dedifferentiation” and/or
“transdifferentiation”) such as osteocytes, chondrocytes, hepatocytes, myocytes,
cardiomyocytes, and even endothelial cells [
5-
9
]. Thanks to these abilities, adult
totipotent (having “unlimited” biological capacity), pluripotent, and multipotent
SCs give rise to repopulation of recipient's BM with subsequent complete, stable,
and long-term reconstitution of hematopoiesis known as engraftment. In addition,
they are also capable of colonizing different tissues (homing) [
9
] . Thus, initial
experimental and clinical studies have shown that “implantation” of autologous
SCs into damaged and/or ischemic area induces their homing and subsequent
“transdifferentiation” into the cell lineages of host organ, including collateral vessel
