April 15, 2010
UK scientists have used nuclear transfer (cloning) technology to create 3-parent human embryos--one father and two mothers.
Despite the standard hype about curing disease using these cloning techniques, significant ethical concerns exist. First, the technique sacrifices two embryos -- the smallest, most vulnerable humans -- to create a third, recombined embryo, with two mothers and one father. It is not a possible cure, but germline genetic engineering and even eugenics, in that embryo manipulation moves us further down the slope not just of selecting children, but manufacturing them.
This technology, described below, is a further step toward tampering with the very essence of humanity, and demonstrates not just a contempt for life itself - all the embryos in this experiment were destroyed for science - but a profoundly dangerous and arrogant belief that we can tamper with the genetic makeup of our fellow human beings.
The rationale for the experiment was that some people have diseases caused by their mitochondria, little energy-generating factories in every cell. Mitochondria have DNA of their own coding for a handful of genes, separate from the nuclear DNA of the cell, and mutations in the mitochondrial DNA can lead to some diseases.
Every cell has mitochondria to generate energy, including the egg cell. When a sperm fertilizes an egg, the mitochondria from the egg cell that contributed to the new embryo are passed to every cell of the person, and if those mitochondria have a mutation, the mutations are passed on as well. The cloning technique used in this experiment was designed to try to get rid of problem mitochondria.
In this human cloning experiment, the scientists used one-cell embryos as both the DNA donor and recipient, an "Embryo Cell Nuclear Transfer". NOTE that most news stories call these embryos "fertilized eggs"; the term is a scientifically inaccurate misnomer and misleading, as once fertilization occurs, these are no longer eggs but rather embryos. The scientific paper published in Nature uses the scientifically-accurate term: "Pronuclear transfer in human embryos to prevent transmission of mitochondrial DNA disease"
After fertilization, but before the maternal and paternal nuclei have joined as a single zygote nucleus, the embryo is at the "pronuclear" stage. The scientists transferred this nuclear material out of one embryo (thus destroying the first embryo), placing the nuclear material into a second embryo (the second embryo having had its nuclear material removed, i.e., destroying the second embryo to make room for the nuclear material of the first.)
Two embryos are destroyed to create (with new genetic mitochondria) a third, recombined embryo. The newly-created recombined embryo has the nuclear material from one embryo, and the cytoplasmic material from another embryo.
A diagram of the process is in the paper's supplementary material.
OR click on this image to enlarge
The scientists let the recombined embryos develop for up to eight days before they were destroyed. As with all cloning experiments, few of the embryos developed. In this case only 18 out of 80 showed any development or divided at all, and only three of the recombined embryos made it to blastocyst stage. This was only half as good as the control "abnormal" embryos (17%), which also develop poorly when compared to normal IVF embryos (32%), again indicating that cloning and manipulation of embryos introduces problems.
When they checked the mitochondria, on average about 2% of mitochondrial DNA was carried over from the first embryo with the transferred nuclear material. The scientists suggested that this was not enough to cause disease, and claimed the experiment as proof-of-principle for a way to prevent inherited mitochondrial disease. However, they have not even shown that such a genetic engineering technique that mixes nuclei and cytoplasm of different individuals is safe even for the newly-cloned embryo and does not affect normal development.
Nonetheless, the UK scientists are supposedly working with the Human Embryology and Fertilisation Authority (HEFA), which licenses research on human embryos in the UK, to determine what further studies must be done before a human embryo that has undergone their genetic engineering procedure can be implanted for a pregnancy.
A similar cloning experiment with mice was done in 2007, and in 2009, U.S. scientists used a similar nuclear transfer cloning technique to create cloned monkey embryos. The U.S. scientists who did the monkey experiments also supposedly have plans to seek approval from the FDA to use their technique to create genetically-manipulated human embryos.