To create human embryonic stem cells, researchers have taken human egg cells, cloned them – just as they did Dolly the sheep back in 1996 – and then reprogrammed them to become embryos.
And they work! These stem cells went on to form various tissues.
However, at least we know the answer to the question: is it possible to make a cloned human embryo? “The clear answer of our paper to this is yes,” says study leader Dieter Egli of the New York Stem Cell Foundation Laboratory.
This cloning technique is called somatic cell nuclear transfer. It usually involves swapping DNA, but in this case, it involves adding the genome of an adult cell to the DNA of an egg.
(Somatic cells are all the ‘adult’ cells in our body that aren’t sex cells, which go on to become eggs or sperm. Somatic cells, have 2 sets of chromosomes, 1 from each parent. Sex cells have 1 total.)
The team ran a series of experiments using 270 eggs from 16 donors (who were each paid $8,000 like in vitro fertilization donors).
- They injected both sets of chromosomes from adult skin cells into unfertilized eggs.
- Then they got the introduced DNA to drive the eggs towards embryonic development.
- Although the resulting embryos have an extra set of chromosomes, they still developed into blastocysts (the hollow ball of cells that forms around day 5 of our development).
- From the blastocysts, the team went on to derive stem cells.
After 63 tries, they got 13 blastocysts and 2 stem cell lines. One carries the genome of a male who has type 1 diabetes, and the other of a healthy male adult.
This is the first conclusive evidence that a somatic cell genome transferred to a human embryo can be reprogrammed to a pluripotent state – with the ability to develop into all sorts of other cells in our body.
Okay, they’re not ‘true’ clones. Since the stem cells have 3 sets of chromosomes instead of the usual 2, the DNA doesn’t match the patient’s. (And our bodies really wouldn’t know what to do with 23 extra chromosomes.) With conventional cloning, the single set of chromosomes in the egg is usually removed… but in humans, the resulting cells stop developing early on and die.
To make this clinically relevant, they’ll need to get stem cells that are genetically matched to the donor. Egli’s group is trying to remove the egg’s DNA and create a viable embryo.
Just how big of a deal is this? According to Nature News, this feat had at times been thought impossible, then inevitable, then completed, then incomplete and unfeasible.
Images from Noggle et al.