Animal implanted with cloned cells hasn’t rejected new tissue; process could make organ transplants much easier
SAN FRANCISCO – A cow implanted with cells taken from a cloned embryo didn’t reject the tissue, showing the potential of much-debated therapeutic cloning, researchers say.
Cloning technology is controversial and opposed by many, including President Bush and Pope John Paul II, because it requires creating and destroying embryos.
However, some scientists who oppose cloning humans say they believe therapeutic cloning should be pursued because it could supply healthy new tissue to fix a variety of illnesses.
“While more work needs to be done, this demonstrates the potential use of this technology,” said Dr. Anthony Atala, director of tissue engineering at Children’s Hospital Boston and a co-author of the study published in the June issue of Nature Biotechnology.
Using healthy cells cloned with the same DNA of a patient could make difficult organ and tissue transplants much easier, Atala said.
In the study, researchers removed the nucleus from a cow egg and replaced it with a skin cell containing DNA from another cow. They then implanted the cloned embryo into a surrogate cow and let the embryo grow for about six weeks before removing it. They removed heart, skeletal and kidney cells from the embryo, grew them further in the laboratory — even creating mini kidneys — and implanted the cloned cells into the cow that donated the DNA.
They removed the cloned cells after six weeks and found all were thriving. Another cloned set of cells was implanted into the same cow and were found to be functional after 12 weeks. Some of the mini kidneys even produced a urine-like liquid, the researchers said.
“It was pretty spectacular and beautiful,” said co-author Dr. Robert Lanza of Worcester, Mass.-based Advanced Cell Technology.
While still far from human use, experts say the latest advance demonstrates the disease-fighting potential of the method.
“It’s a very important result,” said Robert Nerem, director of the Georgia Tech/Emory Center for the Engineering of Living Tissues. “Immune rejection is a very big problem in tissue engineering.”
The report comes three months after other scientists used therapeutic cloning to fix genetic illness in mice.
But the fact that an embryo was grown for six weeks in a surrogate instead of a test tube concerned even some therapeutic cloning proponents.
“While the research in animal models shows that it may be possible to use cloning to generate tissues and eliminate tissue rejection, it’s important for the American public to understand that the methods used in this animal experiment should not be pursued in humans,” said Christopher Reeve, the actor who has become a patient advocate since being paralyzed in a horse riding accident.
“Research involving the implantation of a human embryo into a woman, even to derive lifesaving cells, crosses a very important line and we need to pass legislation that would prohibit it,” he said.
The authors of the paper said they too are opposed to recreating the experiment in humans.
“We think it is ethically unacceptable to implant a cloned embryo in a woman for any purpose,” Lanza said.
There are three competing bills pending in the Senate that address the issue of human cloning. One would ban all forms of cloning, while the others would outlaw cloning to create a baby but allow the technology for use in finding disease cures as long as the embryos were destroyed after a few days and never implanted in women.
“The timing of this study could not have come at a better time,” said Arthur Caplan, a University of Pennsylvania bioethicist who supports therapeutic cloning.