Health and Science Correspondent
June 7, 2002; Washington, D.C. ( Reuters) - Researchers said they had shown cloning can work as a source of grow-your-own transplants, by implanting into cattle cloned cells that formed functioning kidney-like organs and working heart tissue. The cattle's immune systems showed no sign of rejecting the transplanted cloned tissue, said the team from Children's Hospital in Boston and Advanced Cell Technology in nearby Worcester, MA.
The researchers said their experiment, published in the June issue of the journal Nature Biotechnology, should put to rest criticism that therapeutic cloning will not work. "It was pretty spectacular results," Dr. Robert Lanza, Medical Director at Advanced Cell Technology, said in a telephone interview. "Until now therapeutic cloning was theoretical."
The researchers cloned steers, using tissue from their ears to grow tiny embryos. Tissue from these embryos was used to make small, kidney-like organs that functioned normally. "They were making strong yellow urine," Lanza said. "They were removing toxic waste products from the blood at up to 80 percent of what is considered normal for urine."
The whole issue of cloning is hugely controversial around the world. In the United States, Congress is considering either restricting or banning it. President Bush would like to prohibit all cloning involving humans. Most scientists say they do not want to try to clone a human baby, but doctors, patients' groups and many scientists would like to see cloning technology used in medical research. One idea behind this therapeutic cloning approach would be to take a person's cells, and use cloning to grow genetically matched tissues or organs. Possible uses would be in treating diseases in which cells or tissues are destroyed, such as Parkinson's, juvenile diabetes, and stroke. Such cells, it has been postulated, might even be used to grow entire organs. If this could be done, it might take 80,000 Americans off the waiting list for donated organs. An estimated 3,000 die every year waiting for a kidney, heart, liver, or other organ.
NO ANIMAL IS A TRUE CLONE
Critics have said cloning will not work because the Somatic Cell Nuclear Transplant technique used to make Dolly the sheep and other cloned animals does not make an exact genetic duplicate. What the cloning scientists do is get an egg cell, remove its nucleus, and replace it with the nucleus from a cell taken from the animal to be cloned. Various methods are used to start the egg dividing as if it had been fertilized by a sperm cell.
But the resulting animal does not have 100 percent of the DNA from one animal. Virtually all the DNA is in a cell's nucleus, but some is found in the form of mitochondrial DNA, which is in the body of the egg. All cloned animals have the mitochondrial DNA of the egg donor, not of the animal that was cloned. "It's the presence of this foreign DNA that raises the question of whether cloned cells would be rejected," Lanza said.
Opponents of cloning research use this argument to say that no scientific advances will be thwarted if all cloning is banned. "We believe we have shown that this is not the case," said Dr. Anthony Atala of Harvard University and Children's Hospital, who worked on the study.
The team removed some of the tissue from their tiny cloned embryos. They seeded kidney tissue onto artificial structures that they hoped would grow into kidneys when transplanted back into the steer they were cloned from. It worked even better than expected. They self-assembled in the animal," Lanza said. By themselves, the kidney cells formed a small, kidney-like organ. As a comparison the researchers used cells from an unrelated steer to make a similar artificial kidney, and, as expected, the steer's immune system attacked and killed those cells.
They transplanted cloned heart and muscle tissue under the haunch of a second steer, and that tissue also thrived, the researchers said. No one has cloned a human embryo, but Atala said the experiment may be even easier to do in people. The promise of cloning lies in the embryonic stem cells, cells that have the power to become any kind tissue in the body at all.
Experiments on embryos left over from test-tube fertility attempts have shown these stem cells are readily found in a human embryo that is smaller than the head of a pin. If cloning can be shown to work in humans, and if it remains legal, then theoretically a plug of skin could be taken from a patient and used to grow a new heart, brain cells, or other tissue for transplant.