Scientists Say Human Embryos Cloned
South Korean scientists say they have succeeded in creating human embryo clones, a major breakthrough for the promising field of stem cell therapy -- and for the far more controversial endeavor of cloning human beings.
The scientists were able to grow the embryos for several days, extract stem cells from one of them, and then show that the cells could turn into many types of tissues.
The achievement, to be published Friday in the journal Science, was praised by many scientists because it brings closer the possibility that replacement tissues may one day be grown to treat medical conditions such as diabetes, spinal cord injuries and Parkinson’s disease.
But the findings also demonstrate that there is no inherent block to using cloning technology to create babies that are genetic copies of people. Indeed, the paper provides a partial recipe for the correct way to go about it.
Scientists and ethicists urged that laws be enacted to ban any such attempts while permitting research into cloning for medical therapies to continue. They stressed that trying to make human baby clones would not only be ethically questionable but unsafe.
Studies on cloning in animals such as pigs and cows show that many of the embryo and fetus clones die because they contain tiny genetic errors.
“This study doesn’t solve anything about reproductive cloning -- all the real biological problems still remain,” said Dr. Rudolf Jaenisch, a professor of biology at the Massachusetts Institute of Technology.
Experts in stem cells and cloning who had scrutinized the study said that the findings appeared strong, in contrast with the high-profile but unsubstantiated reports of cloned babies that have cropped up over the last few years.
“It’s a stunning achievement, and I think it’s staggering that it has been accomplished so quickly,” said Gerald Schatten, a professor and vice chairman of the department of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh.
While cloning has been achieved in many animals since Dolly the sheep was born in 1996, there has been only one published scientific account of human embryo cloning. It reported that the embryos only grew to about six cells before dying.
Some researchers have suggested that the cloning of primates, including humans, would prove especially difficult because attempts to make monkey clones have been unsuccessful.
However, scientists also said they never doubted that embryo cloning would be achieved in human beings if enough time and money were thrown at the problem.
“Cloning is conceptually very simple,” said Dr. Robert Lanza, medical director of the Worcester, Mass.-based Advanced Cell Technology. “You just need to fine-tune each step of the procedure in each species.”
The study was conducted by a team of scientists at the Seoul National University, Mizmedi Hospital, Hanyang University, Gachon Medical School and Sunchun National University.
A U.S. researcher, Jose Cibelli of Michigan State University, was also a coauthor.
The scientists conducted their experiment not to create human baby clones but to extract stem cells, which have the unique ability to become any type of tissue. To do so, the researchers needed to grow embryos for only several days -- up to the so-called blastocyst stage.
Obtaining stem cells from clones is considered key because it offers the possibility that patients could receive genetically identical tissue that would not be rejected by their immune systems.
In the Science study, the researchers recruited 16 healthy young women who donated a total of 242 eggs. Of these, 176 were suitable for the cloning experiment.
The genetic material was slowly sucked from the eggs then replaced with DNA from a type of body cell known as a cumulus cell. In each case, the egg and the donated genetic material came from the same woman.
The cells were then treated with a chemical to induce division and cultured with nutrients.
The scientists reported that 25% of the egg clones grew to the blastocyst stage. Inside the blastocyst is a small group of cells known as the inner cell mass, which is destined to become the fetus and is the source of stem cells.
From one of the blastocysts, the scientists succeeded in generating a single line of stem cells that could grow in a dish indefinitely.
Under certain conditions, the cells could be induced to form tiny embryo-like bodies that contain a mix of tissue types including skin, muscle, cartilage, bone -- showing the cells were capable of growing into a wide range of tissue types.
While many scientists said the study looked convincing, some pointed out that the experiment did not prove the creation of a clone beyond a shadow of a doubt.
The experiment’s flaw lies in the fact that the egg and donor cell were derived from the same woman. Occasionally, eggs can spontaneously start dividing into embryos, a process known as parthenogenesis.
The scientists attempted to rule this out by performing genetic tests on the stem cells they created, but could not do so absolutely.
“One would want to see this experiment done with a genetically different donor individual,” said David Anderson, a professor of biology at Caltech.
However, other experts said they thought it unlikely that the scientists could have obtained so many blastocysts if parthenogenesis was the cause.
Although producing stem cells from clones is a major milestone in the pursuit of stem cell therapy, it is still a time-intensive process.
In addition, researchers still do not know how to create many kinds of tissues. They do not know whether stem cells will cure diseases or whether they will be stable and not cause cancers.
“We’re still a ways away from the clinic,” said Roger Pedersen, a professor of regenerative medicine at the University of Cambridge in England.
If the South Korean scientists’ research holds up, it raises the possibility that someone could use the technique and implant blastocysts into a woman’s body to create a genetic clone.
Britain has banned human cloning for reproductive purposes. However, such a ban is not in place in the United States.
Even if cloning were perfectly safe, which researchers stress it is not, many are repulsed by the idea of creating genetic replicas of human beings.
Some bioethicists disagree. Gregory Stock, director of the program on medicine, technology and society at UCLA, said society is comfortable with twins, who are genetically identical and yet individuals.
“They are similar in many ways and they are different in many ways,” he said. “I think if anything, cloning would disabuse people of the false idea that clones would simply be a duplication of another person.”
However, Laurie Zoloth, a professor at the Feinberg School of Medicine at Northwestern University in Chicago, said the ability to create clones could have a profound effect on humankind’s perceptions of life and death.
“There is much to reflect on,” she said. “Here is a technology that we have spent literally years thinking about and theorizing about. I have taught it and studied it and researched it and been in hundreds of arguments and debates about it. Yet when the thing is actually accomplished, there is still this sense of crossing a critical threshold.”
