Present at the Future

by Ira Flatow

  Then there’s reproductive cloning, the approach used to create Dolly and other animals with the same nuclear material as an existing animal—or a deceased pet. Scientists transfer genetic material from the nucleus of a donor animal’s adult cell—obtained from the samples you sent in from your pet cat—to an egg whose nucleus, along with it its genetic material—has been removed. To stimulate cell division and growth, the reconstructed egg has to be treated with chemicals or electric current. Once the cloned embryo has developed far enough, it is transferred to the uterus of a female host, where it continues to grow and eventually is born as your new kitten.

  But that means your kitten—and Dolly and other animals created with reproductive cloning—aren’t completely identical copies of the original donor animal. Only the clone’s nuclear DNA is the same as the donor’s. Some of the clone’s genetic material comes from the mitochondria, powerful cells in the egg. Mitochondria contain their own short segments of DNA, and acquired mutations in mitochondrial DNA may play an important part in aging.

  So cloned animals often have unexpected kinks, including much poorer health than their donors. They tend to have compromised immune systems and can be prone to tumors, infections, and other complications. Many cloned animals simply haven’t lived long enough to tell us how clones age. Finn Dorset sheep like Dolly normally live to the age of 11 or 12. Poor Dolly had to be put down by lethal injection in 2003, when she was only 6. She had had lung disease and arthritis, which was crippling her. People with cloned pets often wonder why they lack some of the qualities that made the originals so endearing. Texas A&M researchers once had a sweet-natured bull named Chance. They liked him so much that they cloned him and dubbed the clone Second Chance. Unfortunately, Second Chance turned out to have a dangerous temper; he was much more of a raging bull.

  Reproductive cloning also is hard to do. More than 90 percent of cloning attempts fail to produce healthy offspring, and more than 100 nuclear transfer procedures may be needed to make one successful clone. Dolly, for example, was a single success out of 276 attempts. Scientists hope to use this method to reproduce animals that have been genetically engineered to produce useful drugs, or to serve as models for studying human disease. Researchers also would like to repopulate endangered animal species or those that are difficult to breed, such as pandas. But that remains a major challenge. (Cloning extinct animals would be even more difficult, because the egg and the surrogate mother would have to belong to different species from the clone.) So far, certain animal species, such as chickens, have resisted attempts to clone them. Cloning has been limited to only a few animal species, and some species may turn out to be more resistant to reproductive cloning than others.

  THERAPEUTIC CLONING

  The third type of cloning is called therapeutic cloning, and it involves the use of cloning technology in medical research. One day, it may allow the production of whole organs from single cells and make waiting lists for donations of organs such as the liver, kidney, or heart a thing of the past. Or therapeutic cloning could produce healthy cells that could replace damaged cells in degenerative diseases such as diabetes, Alzheimer’s, and Parkinson’s.

  In 2002, one biotech company reported that its researchers had successfully transplanted kidneylike organs into cows. The team created cloned cow embryos by removing the DNA from donor cow egg cells, and then injecting the DNA from skin cells of a donor cow. The scientists allowed these cow embryos to develop into fetuses. Then they harvested fetal tissue from the clones and transplanted it into the donor cow. After three months, the team reported that they had not observed any organ rejection in the donor cow.

  XENOTRANSPLANTATION

  Another way that scientists are trying to make therapeutic cloning work is to create genetically modified pigs and harvest from them organs for transplantation to humans, or xenotransplantation. Pigs are good candidates for therapeutic cloning and xenotransplantation because their tissues and organs are quite similar to humans’. To create what British scientists call knock-out pigs, they have to inactivate the pig genes that trigger the human immune system to reject a transplanted pig organ. They knock those genes out of individual cells, which they then use to create clones from which they can harvest needed organs. In 2002, a British biotech firm reported that it had produced the first “double knock-out pigs,” genetically engineered to lack both copies of a gene involved in transplant rejection.

  One potential hazard of using organs from animals such as pigs is the possibility that some viruses that live in the pigs might find their way into humans and kill the recipient. This possibility is making xenotransplants still very controversial and in need of further research.

  EMBRYONIC STEM CELLS

  Therapeutic cloning often is described as stem cell research because both involve growing stem cells. What scientists need to grow human replacement parts are human stem cells, “blank” cells that have not yet decided what they will become. They might become heart, or lung, or brain cells; they are just awaiting genetic instructions. The easiest place to find and extract such stem cells in large quantities is the blastocyst, a ball of cells that forms in the first few days after a sperm and an egg join. These cells—about 32 to 200—are the foundation cells for every organ, tissue, and cell in a human body. These stem cells have not yet differentiated themselves into the more than 200 kinds of specialized cells that can become blood, neurons, skin, or organ tissue in a human body. In 1998, biologists at the University of Wisconsin reported that they had succeeded in using cloning technology—removing cells from human embryos—to establish the world’s first embryonic stem line, or population, in the lab. The Wisconsin stem cells—along with most embryonic stem cells used for research—were extracted from embryos created by in vitro fertilization and were left at fertility clinics, frozen in liquid nitrogen, as spares by couples who already had succeeded in conceiving healthy children. (A small percentage of couples donates the spares to research.)

  A blastocyst is no bigger than the period at the end of this sentence. Its inner cell mass contains 8 to 40 stem cells. Once the stem cells have been transferred into culture, they begin to proliferate. If after several months the original cells have grown into millions of healthy cells, without starting to differentiate into specialized cells, then they are known as an embryonic stem cell line, or colony. A line can replicate indefinitely in a lab—although stem cells do deteriorate as they age and accumulate genetic mutations. So researchers are always looking for new supplies of stem cell lines.

  Adults have a small number of stem cells in many of their organs and tissues, including their blood, heart, skin, bone marrow, and skin. Adult stem cells also can be found in liposuctioned fat, pulp under baby teeth, amniotic fluid, placentas, or a newborn’s umbilical cord. But adult stem cells are scarcer in the body and harder to grow in the lab than embryonic stem cells, and they don’t seem to be as versatile: They might be limited to becoming cell types within the tissue where they are found. (Cord cells produce blood cells and may prove capable of generating bone and cartilage cells.)

  Stem cell research for therapeutic cloning still is at a very early stage. Scientists are working to figure out how to direct stem cells to treat heart disease, leukemia and other cancers, burns, Parkinson’s disease, rheumatoid arthritis, and diabetes and to regenerate nerve cells in patients with spinal-cord injuries. (Christopher Reeve, the actor paralyzed in a 1995 riding accident, campaigned tirelessly for stem cell research until his death in 2004. Michael J. Fox, the actor who has Parkinson’s disease, has picked up where Reeve left off.) So far, only adult stem cells have been tested in humans, although research continues in search of treatments for many different diseases.

  To generate organs or tissues for transplant, scientists would extract DNA from the patient in need and insert it into a donor egg from which the nucleus and genetic donor material have been removed. After the egg, which now contains the patient’s DNA, begins to divide like a regular fertilized egg, it forms the
early embryo, or the blastocyst ball of cells. Scientists would remove the stem cells and use them to grow any kind of tissue, nerve cell, or organ needed to treat the patient.

  RELIGION AND POLITICS: SOLUTIONS?

  In the United States in 2001, President George W. Bush put extreme limits on allowing federal money to finance research using embryonic stem cells if that research destroys the embryo, because the president believes that is equivalent to killing a person. The Catholic Church also teaches this belief, and other people feel the same way who believe that life begins at the moment of fertilization. Since fertilized eggs are usually destroyed in embryonic stem cell research, the president, as well as others of the same view, believes that embryonic stem cell research should not be permitted.

  But new research may offer a solution to that dilemma. Scientists have been able to extract and grow embryonic stem cells without harming the embryo. They say they can pluck a single cell from a blastocyst of less than a dozen cells, leaving the embryo intact, and using that cell to create a line of stem cells. This new method is based on a procedure that is routinely used in fertility clinics to test lab-created embryos for genetic disorders.

  “It’s relatively simple and does not injure the embryo. In fact, it’s been used for years to generate thousands of healthy babies,” says Dr. Robert Lanza, medical director and research team head at Advanced Cell Technology in Worcester, Massachusetts.

  “During this procedure, a single cell is normally removed from an eight-cell stage embryo and then sent off to the laboratory for genetic testing.”

  What Lanza is proposing is that they simply let that cell grow overnight, send one of the resulting cells off for testing, and then use the remaining cell or cells to create stem cells. “Thus, it will not interfere at all with the clinical outcome in any way. It will not affect the chances of the couple having a child. So there’s absolutely no added risk for the embryo, but there’s very much a positive benefit.

  “These stem cells would also be of value to the siblings as well as to the scientific community, who of course could use these since they are immortal and would continue to grow indefinitely. So again, our main goal here would be to increase the number of stem cell lines that are available for federal funding and thus give this field a badly needed jump-start.”

  Would this new technique, which does not harm the embryo, change the mind of those against embryonic stem cell research? Lanza is not sure. “Embryonic stem cell research has been synonymous with the destruction of an embryo for so long, it’s hard to imagine those individuals coming around, at least in the short term, but I think it really does remove the last rational objection to stem cell research.”

  The removal of cells for genetic testing in in vitro fertilization labs has been going on for many years. It’s quite common. So why did Lanza and his colleagues have success where others have not? Why didn’t anyone think of this before?

  “It turns out [that] to derive embryonic stem cells is actually pretty tricky,” he points out, even for the most experienced researchers. “Those early stages of derivation—it’s just very easy to lose the stem cells. And what we’re talking about here is actually removing a single cell even at an earlier stage. You’re talking about normally generating cells from a blastocyst—a clump of cells that’s anywhere from sixty-four to two hundred cells—whereas the embryo we’re removing this from is only eight cells.”

  The key to his success, Lanza believes, is putting the removed cell into a petri dish with other similar cells. “People in the past were just pulling it out of the embryo and throwing it in a plastic dish, and of course, the cell isn’t happy and it dies.” How do you make an embryonic stem cell happy? Give it companionship. “We know that embryos like to be together. If you put two or three embryos in a dish, for instance, they will grow much more strongly. The same with embryonic stem cells. If you only have a few, they tend to die. They’re social creatures.” So it’s not surprising that a cell that’s talking with its neighbors—that is, it’s trying to decide how to become a full organism with all the organs and tissues—that if it’s plucked out and put in a dish, it has been shut off from communicating, and it dies. “It can’t talk to any neighboring cells, and it doesn’t know what to do.”

  AMNIOTIC STEM CELLS

  Just a few months after the Lanza announcement came word, in January 2007, of an even more intriguing stem cell advance: the isolation and growth of stem cells taken from amniotic fluid. “They appear to have the ability to change into many types of tissue in a similar way that embryonic stem cells do,” says Dr. Anthony Atala, professor and chair in the Department of Urology and director of the Institute for Regenerative Medicine at Wake Forest University Baptist Medical Center in Winston-Salem, North Carolina. For almost a decade Atala and his colleagues wondered: “‘Could we find a population of true stem cells in the amniotic fluid and the placenta?’ And the answer was indeed, there was a true stem-cell population that could be found both in the amniotic fluid as well as the placenta, which is the tissue, of course, that surrounds the baby and the fluid during development.”

  They are not embryonic stem cells, says Atala. “They’re a class of [their] own. They’re neither embryonic nor adult, but they have properties of both.” For example, they are closer to human embryonic stem cells not only because they are so young “but [also because] like human embryonic stem cells, the cells are able to grow very rapidly. They double in number every thirty-six hours, which is one of the advantages, of course, of human embryonic stem cells. We also found markers consistent with human embryonic stem cells, but to our surprise, after we started growing these cells, we also found markers consistent with adult stem cells.”

  Atala has been able to prod these stem cells into doing what they do best. He’s been able to direct them to become different tissue types: nerve, liver, muscle, cartilage, bone, and others. But only in the laboratory. “This is still very early in its development stage. It’s going to take a while before we’re able to bring these technologies to patients.”

  But because these cells come from people, would tissue made from these cells be rejected in recipients? “That’s actually another nice advantage of these cells,” points out Atala. “The fact is that you can preserve these cells after birth or during birth, if they have an amniocentesis. You could preserve these cells for self-use. So you can just freeze these cells now, and then use these cells if there’s ever any problem with that particular patient.”

  But there is a second way to use these cells, and that is by creating a cell bank that would be available to other patients for transplant, the way a kidney or liver or heart is available now. You would find a donor “match” among the thousands and thousands of cells in the cell bank, says Atala. “This has all been worked in the transplantation field. You would need a bank of approximately one hundred thousand specimens to be able to provide ninety-nine percent of the U.S. population with a perfect genetic match for transplantation.

  “And that would be a lot easier to do with this source of cells, because, as you know, there are approximately 4.5 million births per year in the U.S. So every birth could be a potential source of stem cells from the afterbirth, or what we call the placenta, and we could just retrieve those cells, bank those cells, and then have those available for other patients when the need arose.”

  The ability of these amniotic stem cells to transform into other tissues does not mean that embryonic stem cell research should be curtailed, says Atala.

  “These are different from human embryonic stem cells; these are different from adult stem cells. And we don’t know yet, long term, which cell would be best for what particular application. I think all research is important because we just don’t know what cell is going to be best for what particular disease process.”

  Atala is continuing to refine his research, poking his stem cells to function at the same level as the normal cell. “They are actually secreting the things they’re supposed to be secreting, and they
are hooking up together with each other like they’re supposed to do. We have a lot of work to do still. Even though it’s exciting, of course, it’s still in its early stage of development.”

  PEOPLE: A CLONING NO-NO

  While there has been talk from rogue scientists about cloning people, and while there is no federal American law banning cloning, many scientists and physicians and organizations such as the American Medical Association and the American Association for the Advancement of Science believe that human reproductive cloning is unwise, if not unethical. Most attempts to clone animals fail, with only one or two healthy offspring for every 100 experiments. Many cloned offspring who seem healthy die prematurely. And no one knows how cloning could affect mental and emotional development in humans.

  ACKNOWLEDGMENTS

  It is my good fortune to know many smart and talented people whose work on my behalf made this book possible. Foremost are my stalwart producers on Science Friday—Charles Bergquist, Annette Heist, and Karin Vergoth—who spend the many hours preparing the interviews that take place on NPR’s Talk of the Nation: Science Friday each week. It is those interviews that served as the backbone for this book.

  My eyes were opened to the mythology of why airplanes fly by Norman Smith, but I could never quite nail down the physics until I read the works of Dr. David Anderson. He was good enough to send me a PowerPoint presentation for a lecture he gave at Fermilab on the physics of flight, as well as his terrifically illustrated book Understanding Flight, written with coauthor Scott Eberhardt. One look, and I had the solid grounding in science I needed to overturn that myth, which had been festering in my mind ever since I had met Smith many years ago.

  For two key illustrations—the double-walled nanotube jacket cover and the rare photo of a jet slicing through the clouds—I’m indebted to Chris Ewels for his out-of-this-world carbon nanotube illustrations and to Paul Bowen for the permission to use his unique jet-in-the-clouds photo.