Human embryonic stem cells (hESC), new cells that are basically a biological blank slate, become more specialized as they develop and contribute to a number of organs and tissues. As such, they have the potential to treat diseases such as Parkinson’s but their progress has been slowed because of the ongoing ethical debate over how human embryonic stem cells are derived.

Some European countries - Austria, Germany, Ireland, Italy, Norway, Poland, Slovakia and Switzerland - forbid the creation of new hESC lines surplus embryos, even ones that remain from infertility procedures. In June, 2006 the EU parliament only narrowly agreed to fund stem-cell research, and then only as long as it excluded activities that involve destroying human embryos. In the US the restrictions are similar. In August 2001, President George W. Bush limited federal support to research that uses the hESC lines that existed before that date.

A recently published paper by Dartmouth Professor Ronald M. Green ( subscription required) lays out the ethical and scientific feasibility of deriving embryonic stem cell lines without destroying living human embryos.

“The six approaches differ in technique, most directly in how the blastocyst is created.” The blastocyst, where embryonic stem cells are found, is the three- to five-day-old embryo that has not yet been implanted in a uterus. “Since many people regard the normal human blastocyst as morally deserving of protection, the challenge is to find methods of deriving hESCs that either leave the blastocyst intact and unharmed or avoid the use of normal blastocysts in the first place.”

The six approaches he discusses are:

  • Altered Nuclear Transfer - Richard Hurlbut, a member of the President’s Council on Bioethics in the
    United States, advocates this approach. It uses somatic-cell nuclear transfer technology to create embryo-like entities that can be separated to produce hESC lines. This is the same approach that is used in therapeutic cloning research.
  • Parthenogenesis - development of an embryo directly from an oocyte without fertilization by sperm. Because this lacks 'paternal imprinting' it's unclear how effective this will be for transplants.
  • Single-blastomere Biopsy - A single blastomere is removed by microsurgery at the 8–16-cell stage. After the cell is cultured is divides and one daughter cell can be used for genetic
    diagnosis and the other for the creation of an hESC line. While scientifically validated by experiments, this remains ethically divisive. In the US, regulations forbid research on a fetus that imposes greater than minimal risk, unless the research is for the direct benefit of the fetus.
  • Somatic-cell Dedifferentiation - The Holy Grail of stem cell research, this is taking any differentiated body cell and reverting it. Ethically it's okay because ruling out somatic cell manipulation rules out virtually the entire grooming and hygeine industries but it's a long way off and experimentation to get this working many involve approaches that generate the ethical controversy that needs to be avoided.
  • The Use of “Organismically Dead” Embryos - At first glance this is similar to cadaver organ donation so would be no problem. However, to create a stem-cell from a dead embryo it must have some viable cells and then the issue becomes when an embryo is dead. In people, we have vital organs so declaring death is easy but embryos don't have such a simple metric.
  • The Use of Abnormal Embryos - It's common in fertilization procedures to set aside chromosomally abnormal embryos. A recent study said that 'normalization' could occur in those embryos but there are scientific and ethical obstacles. It's unclear if the embryos can produce stable stem cells for transplant purposes and people are going see a eugenics slippery slope in the destruction of embryos of disabled or genetically diseased people.

The full paper explains the detailed science behind the six approaches and further describes the hurdles that must be overcome in making them useful in future stem cell research.

None of these options is free from scientific challenges or ethical and political controversy but continuing to search for answers is the only solution and this shows that scientists are continuing to try and be respectful to the mores of society while advancing progress in medicine.

“I think we can pursue hESC research and also respect the sensitivities of our fellow citizens. It’s not impossible to do both,” says Green, faculty director of the Dartmouth Ethics Institute. The goal is to make stem cell lines that are ethically universal. “These would be analogous to the universal O-type blood group: lines that could be used by anyone regardless of their ethical views on the moral status of the embryo."