By adding the nuclei of adult skin cells from patients with type 1 diabetes to unfertilized human eggs without first removing the egg DNA as was done to clone Dolly the sheep, scientists at a stem cell lab in New York have managed to reprogram the eggs to an embryonic state and make a self-reproducing line of embryonic stem cells from the quasi-cloned embryo. The embryo is not a true clone of the donor patient because it has three sets of chromosomes: two from the patient and one from the egg itself. However, it is a step in the right direction and the achievement appears to have overcome some of the difficulties that have evaded scientists since the Dolly days.
You can read how researchers at the New York Stem Cell Foundation Laboratory used cloning technology to reprogram adult human egg cells to an embryonic state in the 4 October online issue of Nature.
Using stem cells to regenerate damaged or lost tissue, scientists hope one day to develop safe and effective cures and treatments for debilitating diseases like Parkinson’s, Alzheimer’s, diabetes and others that affect millions of people around the world.
But making stem cells in a cost-effective and safe way has proved more elusive than first thought, since scientists first cloned Dolly the sheep back in 1996.
Stem cells are “master cells” that under the right conditions can become any kind of cell in the body: they are “pluripotent”. The “best” stem cells are the embryonic stem cells: these can become virtually any type of cell and are naturally pluripotent. However, there are ethical problems with harvesting embryos and you need a lot of them.
Another type of stem cell is the so-called induced pluripotent or “iPS” stem cell which is made by inserting a few genes into mature cells to reprogram them to an embryonic-like state, obviating the need to use an entire egg. These iPS cells have the advantage of having the same DNA as the donor patient who needs the new tissue, but since they arrived on the scene in 2006, we have discovered iPS cells differ from embryonic stem cells in subtle but important ways, we are still a long way from deriving safe and useful stem cell treatments from this method.
So, a way to overcome the ethical problems of using embryos and the problems with iPS, could be to go down the cloning route that began with Dolly the sheep. It seems straightforward: take a human egg, strip away the egg DNA and insert the DNA of the patient who needs the new tissue and wait for the egg to divide. However, this method is also fraught with problems, for a start you need an awful lot of eggs (not a problem when you are working with sheep) because the process is very fiddly and many cells just don’t get past a few divisions.
In 2004, a group of scientists led by Woo Suk Hwang, then a biologist at Seoul University, said they had made a viable cloned human embryo, but it turned out the results had been faked and they had used more than 2,000 eggs obtained unethically. The aftermath of this “study” raised serious questions about the legal and moral implications of using human eggs for research.
So study leader Dieter Egli, a researcher at the New York Stem Cell Foundation Laboratory, and colleagues decided to start from scratch. They ran a series of experiments using 270 eggs from 16 donors to try and pinpoint the step in the cloning process that was causing the problems. They established it was the step where the egg DNA is removed: so they tried cloning without removing the egg DNA: in effect coaxing an egg cell with three sets of chromosomes, two from the donor patient and one from the egg, to divide.
The reprogramming worked and the quasi-cloned “embryo” (with three sets of chromosomes) reached the blastocyst stage, which contains about 70 to 100 cells from which you can make stem cells.
Egli told Nature News he was surprised “that it actually worked. Our result really proves the technical hurdles can be overcome.”
Robert Lanza specializes in developing therapies that use stem-cell technology. He is chief scientific officer at Advanced Cell Technology, a company based in Santa Monica, California and was not involved with the study. He said the work Egli and colleagues have done “clearly shows the enormous power of this technology”, and that “human eggs do indeed have the magic we thought they did!”
But he is cautious about this particular experiment, pointing out the method has not been tried before, and also that it has no “clinical relevance” because the stem cells are not compatible with the patient’s tissue since they have the extra set of chromosomes.
However, as more news breaks about the iPS cells, scientists may well search for more “natural” ways of reprogramming cells using cloning.
In the meantime Egli and his group are trying to understand more about egg chromosomes and what factors they have that help the cell divide and reach the blastocyst stage, that aren’t in the chromosomes of mature cells.
Speaking to Nature News, Lanza said he thinks it could be that when you take the chromosomes out of the egg you also remove the spindle apparatus necessary for cell division, something that may not be so critical for other species.
Egli said in a statement that:
“Our hope is that we can eventually overcome the remaining hurdles and use patient-specific stem cells to treat and cure people who have diabetes and other diseases.”
Written by Catharine Paddock PhD