Biomedical Engineering Reference
In-Depth Information
past decade, the use of cord blood has expanded rapidly. Cord blood has been used
to transplant in any disease state for which bone marrow can be used in spite of
some disadvantage—rather small number of cells collected in each unit; delayed
engraftment of neutrophils is common with cord blood. In addition to bone marrow
and cord blood, peripheral blood stem cells (PBSCs) have gained popularity as a
source of stem cells since their initial introduction in the 1980s.
Stem Cells Nowadays
The late 1990s brought a new apprehension regarding the biology of stem cells. In
1998, researchers at the University of Wisconsin led by James Thomson isolated
and grew stem cells from human embryos, and researchers from Johns Hopkins
University led by John Gearhart did the same for human germ cells [
11
] . In 1999
and 2000, researchers began to find that manipulation of adult mouse tissues could
sometimes yield previously unsuspected cell types; for example, that some bone
marrow cells could be turned into nerve or liver cells and that stem cells found in the
brain appear to be able to form other kinds of cells.
The current knowledge related to the stem cells in 2005 comprises:
•
Stem cells are the body's “master” cells.
•
Stem cells can renew themselves indefinitely and differentiate into any of a num-
ber of types of specialized cells, such as muscles, nerves, organs, bone, and
blood.
Stem cells “plasticity”—ability to become other types of cells—makes them
•
essential for repairing and renewing body tissues throughout our lives.
After we are born, our body retains stem cell reserves in various organs and,
throughout our lives, we tap into those reserves to repair and replace injured or
diseased tissues. Unfortunately, our stem cell reservoirs are finite and, as they
become depleted, we succumb to diseases, disorders, and the ravages of aging.
Thus, stem cell therapy offers the potential to replenish our exhausted reserves and
fight a wide variety of diseases and disorders.
Summary
Stem cells are the key subset of cells in the body functioning as ancestor cells to
produce a variety of types of functionally specialized mature cells (differentiation)
in a given tissue, while at the same time maintaining the capacity to continuously
divide and reproduce themselves (self-renewal). This self-renewal process is con-
trolled by intrinsic genetic pathways that are subject to regulation by extrinsic sig-
nals from the microenvironment in which stem cells reside. Stem cells play essential
