US scientists have created early human embryos for the first time by using DNA taken from human skin cells and then fertilizing them with sperm.
The method could help overcome age-related or disease-related infertility, because almost any cell in the body can be used as the start of a new life.
Even same-sex couples could have their own genetically related children through this technology.
The method still needs extensive refinement—which could take at least a decade—before any infertility treatment center can consider using it.
Experts have described it as a significant scientific breakthrough, but they say the new scientific possibilities need to be discussed openly with the public.
Reproduction used to be a very simple process—a man's sperm meets a woman's egg, they form an embryo, and nine months later a baby is born.
But now scientists are changing that rule. In the latest experiment, it has been possible from human skin.
The method used by the Oregon Health & Science University research team involves extracting the nucleus (which contains the complete genetic code needed to build a human body) from a skin cell.
This nucleus is then placed into a donor egg that has had its own genetic instructions (DNA) removed.
The process is similar to the one used to create Dolly the Sheep, the world's first cloned mammal, in 1996.
However, the egg is not yet ready to be fertilized by a sperm because it already contains a complete set of chromosomes (the complete set of DNA instructions).
Normally, a person inherits 23 chromosomes from their mother and 23 from their father, for a total of 46. But now this egg contains 46 chromosomes.
So the next step for the researchers is to convince the egg to shed half of its chromosomes, so that it is down to 23 and can combine with the sperm's 23 to form a full set of 46.
The researchers have called this process 'mitomeiosis', which is a combination of two cell division processes—mitosis and meiosis.
The new method, published in the journal Nature Communications, produced a total of 82 viable eggs.
The eggs were then fertilized with sperm, and some of them reached the early stages of embryo development. However, none of the embryos developed beyond six days.
“We have achieved something that was previously thought impossible,” said Professor Shokhrat Mitalipov, director of the Center for Embryonic Cell and Gene Therapy at Oregon Health & Science University.
The method is not yet perfect, because the egg randomly selects the chromosomes it will discard. It should keep one of each of the 23 types of chromosomes to ensure a healthy embryo, but instead sometimes two identical copies of some chromosomes remain, or in some cases none at all.
The success rate of the method is also very low (about 9%) and the chromosomes do not participate in a crucial process called ‘crossing over’, where they naturally rearrange their DNA.
Professor Mitalipov, a world-renowned pioneer in the field, said, “We need to get it right.” I think this is the only way forward, because more and more patients are unable to have children.
The technology is part of a growing field that aims to create sperm and eggs outside the body, known as in vitro gametogenesis.
It is still in the research stage and is not ready for clinical use.
The technology aims to help couples who cannot use IVF (in vitro fertilization) because they do not have viable sperm or eggs.
It could help older women who no longer have viable eggs; men who cannot produce enough sperm; or patients who have been infertile due to cancer treatment.
The rules of paternity would also have to be rewritten. The method described does not have to use skin cells from the woman—it could start from skin cells from the man.
It is a new opportunity for same-sex couples to have children who are genetically related to both parents.
For example, in a male same-sex couple, eggs could be created using the skin of one man and fertilized with sperm from another man.
Professor Paula Amato of Oregon Health & Science University said: “In addition to offering hope to the millions of people suffering from infertility due to lack of eggs or sperm, this procedure would open up the possibility of a child for same-sex couples who are genetically related to both parents.”
Professor Roger Stormy of the Department of Reproductive Medicine at the University of Hull said: “This science is important and fascinating.”
“At the same time, such research also reinforces the importance of having an open dialogue with the public about the progress of new reproductive research,” he added.
“This kind of progress tells us that we need robust regulatory mechanisms to ensure accountability and build public trust,” he said.
Professor Richard Anderson, deputy director of the MRC Centre for Reproductive Health at the University of Edinburgh, said the ability to create new eggs would be “a significant advance.”
“There will be significant safety concerns, but this research is a step towards enabling many women to have their own genetic children,” he said.
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