Somatic Cell Nuclear Transfer

Another way to create stem cells is by taking a human egg (oocyte) and removing the nuclear DNA – the DNA that holds the programming for the majority of the genetic characteristics of the person. The original nuclear DNA is replaced with the nuclear DNA from a donor cell. That donor DNA comes from another human or non-human animal. The oocyte now contains the entire complement of DNA rather than just the half it originally contained. When that oocyte is stimulated in the laboratory  it begins to divide and becomes a blastocyst with the same genetic make-up as the donor. Once the reprogrammed oocyte reaches blastocyst stage hES cells can be extracted from the inner cell mass and used to create a cell line in culture in a laboratory. This is a very powerful tool because the stem cells in the newly created cell line are a genetic match to the donor of the nuclear DNA that reprogrammed the oocyte. This potentially enables researchers or clinicians to create genetically identical tissue for tissue replacement. When genetically identical tissue is used in transplantation,  the medical complications of rejection by the transplant recipient’s immune system are eliminated and with that the need to take expensive, immune-suppressing drugs.



This technique is called nuclear transfer since the nucleus of one cell is transferred to another. It is also known as somatic cell nuclear transfer (SCNT) since a cell from the body tissues (a somatic cell) is used in the nuclear transfer. Somatic cell nuclear transfer is a type of reprogramming technique that is also used in “cloning” technology. For this reason the creation of embryos by SCNT in hES research has been variously referred to as “research cloning” and “therapeutic cloning.” Until such time as there are clinically available applications  of this technique, the most appropriate description would be “research cloning.” Many authors have opined that the use of the term “cloning” has created a tempest about the use of SNCT. While SCNT may be a cloning technique it does not result in a baby or living clone.  The use of cloning techniques to create genetically identical embryos that are then implanted in a woman who gives birth to a genetically identical child (a kind of intergenerational identical twin to the DNA donor), is called “reproductive cloning.” It has been widely prohibited  around the world, and is prohibited under Canada’s Assisted Human Reproduction Act.

SCNT is used to create hES cell lines necessary for autologous transplantation and for the creation of disease-specific cell lines. Due to the fact that it is a cloning technique and that people are fearful about reproductive cloning, there has been significant controversy about this method of creating hES cell lines. There are ethical arguments against using SCNT to create embryos for research. These include arguments against creating embryos for an instrumental purpose and against the endorsement of a technique requiring a large source of human eggs since this may lead to the exploitation of women. These arguments are discussed in Knowles  L., “The Use of Human Embryos in Stem Cell Research” Stem Cell Network, and Knowles L., “Commercialization and Stem Cell Research” Stem Cell Network.

Other arguments against using SCNT to create embryos reflect a fear that using such a technique could lead
to reproductive cloning. This is not primarily an ethical objection but evidence either of confusion between the two uses of cloning technology – one for research and eventually therapy, and one for reproduction – or a lack of trust in stem cell scientists. The lack of trust indicates that people are fearful that scientists may move from research cloning to reproductive cloning, as in sliding down a slippery slope. To date this has not happened, but rigorous professional standards among stem cell scientists and infertility clinicians are a crucial part to maintaining the integrity of the research and people’s trust. SCNT remains today a powerful technique to harness the potential of stem cell research through creating cell lines with a specific genetic makeup.