If research with
embryonic stem cells continues, the source of these cells will become an issue. Embryonic stem cells are taken from the early embryo, shortly after fertilization. At present, embryos that are frozen for couples undergoing in vitro fertilization are used to collect embryonic stem cells. Generally, due to the high failure rate of the procedure, multiple eggs are fertilized and stored. These are then transplanted into the mother one at a time until she becomes pregnant. The remaining embryos remain in storage and are generally forgotten. They present a potential limited source of stem cells as long as the issue of tissue rejection is not addressed.
More recently a new technique has been developed called
somatic cell nuclear transfer (SCNT). SCNT involves the removal of an
egg from a hormonally treated female. The donor egg is enucleated and the nucleus of a somatic cell is transferred into its cytoplasm (nuclear transfer). The egg is then stimulated to start dividing. After sequential cell divisions, the
blastocyst formed contains cells that will give rise to all tissues in the embryo. The blastocyst can be used to generate embryonic stem cells, which are genetically identical to the somatic cell donor, thereby eliminating the possibility of rejection when transplanted.
Reproductive cloning
Alternatively, the blastocyst can be implanted back into a female and brought to term resulting in a
cloned organism. This procedure was allegedly used in the production of the first cloned human mentioned above.
SCNT was pioneered by Dr. Ian Wilmut at the Roslin Institute in Scotland. He used this technology to produce the world's first cloned sheep, Dolly, in 1996. Unfortunately, she developed arthritis early in life and showed premature signs of aging. Dolly was euthanized in February 2003 after doctors detected a progressive lung disease. She had only reached half the lifespan of a typical sheep and, while it has not been proven that her cloned status played a part in her early death, scientists remain sensitive to the fact that the full implications of this technology are not yet known. Since 1997, this technology has been used to clone pigs, mice, goats and cats. In November 2001, the production of the first human embryo by this method was reported in the Journal of Reproductive Medicine.
More abstracts about the Human Cloning: Science Fiction or Reality?