Biomedical Engineering Reference
In-Depth Information
Pluripotency of Human Embryonic Stem Cells
and Embryonic Germ Cells
A truly pluripotent stem cell is a cell that is capable of self-renewal and of
differentiating into most all of the cells of the body, including cells of all three germ
layers. Human ES and EG cells in vitro are capable of long-term self-renewal, while
retaining a normal karyotype (Andrews PW, personal communication; Bongso A,
personal communication) [ 1, 5- 15, 28 ]. Human ES cells can proliferate for two
years through 300 population doublings [ 26- 28 ] or even 450 population doublings
[ 27 ]. Cultures derived from embryoid bodies generated by human embryonic germ
cells have less capacity for proliferation. Most will proliferate for 40 population
doublings; the maximum reported is 70-80 population doublings [ 29 ] .
Several laboratories have demonstrated that human ES cells in vitro are pluripo-
tent; they can produce cell types derived from all three embryonic germ layers (Pera
M, personal communication) [ 1, 18, 30 ]. Currently, the only test of the in vivo pluri-
potency of human ES cells is to inject them into immune-deficient mice where they
generate differentiated cells that are derived from all three germ layers. These
include gut epithelium (which, in the embryo, is derived from endoderm); smooth
and striated muscle (derived from mesoderm); and neural epithelium, and stratified
squamous epithelium (derived from ectoderm; Pera M, personal communication)
[ 4, 18, 29- 37 ]. Currently, a major goal for embryonic stem cell research is to control
the differentiation of human ES and EG cell lines into specific kinds of cells—an
objective that must be met if the cells are to be used as the basis for therapeutic
transplantation, testing drugs, or screening potential toxins. The techniques now
being tested to direct human ES cell differentiation are borrowed directly from tech-
niques used to direct the differentiation of mouse ES cells in vitro .
What Are Potential Uses of Human Embryonic
Stem Cells in Tissue Engineering?
Many uses have been proposed for human embryonic stem cells. The most-often
discussed is their potential use in transplant therapy or tissue engineering—i.e., to
replace or restore tissue that has been damaged by disease or injury.
Using Human Embryonic Stem Cells for Therapeutic
Transplants
Diseases that might be treated by transplanting human ES-derived cells include
Parkinson's disease, diabetes, traumatic spinal cord injury, Purkinje cell degenera-
tion, Duchenne's muscular dystrophy, heart failure, and osteogenesis imperfecta.
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