The promise of new therapeutic avenues for the treatment of a range of conditions has led researchers to consider the use of stem cells. These cells have the capacity to become some or even all of the 206 different cell types found in the human body. It has even been suggested that one day stem cells may be able to form whole organs and hence contribute to organ transplantation therapies. Stem cells come in a wide variety of types. Adult stem cells have been found in nearly every tissue of the human body, where they carry out a role in tissue regeneration. Embryonic stem cells are located in the human embryo at the blastocyst stage (5 to 6 days of age). Embryos at this age are often unwanted in reproductive technology treatment, and some parents have donated them for research. Cord blood stem cells are derived from the umbilical cord which is often still routinely discarded at birth.
The key ethical issues concern the destruction of human embryos for stem cell derivation. On the grounds that the human embryo is a human life with moral value justifying its protection, the extraction of embryonic stem cells is unethical. The use of adult stem cells and umbilical cord blood stem cells have generally been considered to be free of any particular ethical issues. In fact they have been applauded as ethically superior alternatives to the use of embryonic stem cells.
One limitation to the possible use of embryonic stem cells in therapy is that they will likely be rejected by the recipient. In an attempt to overcome this researchers are attempting to produce cloned human embryos to derive genetically near-identical stem cells for possible treatment.