Stem Cell Research: Science and the Future
Stem Cell Research: Science and the Future
February 14, 2006
by Terry Gross
Fresh Air from WHYY, February 14, 2006 · Since 1998, when scientists isolated embryonic stem cells in a lab, questions over how -- and whether -- to use them have abounded. In Stem Cell Now, bioethics expert Christopher Thomas Scott explores the possibilities of what some consider the greatest discovery since nuclear fusion.
The book details what Scott calls a revolution in research, as the potential for freely available cells that can help repair or rebuild the human body is still being explored.
But while his main concern is the science behind stem-cell research, Scott also takes pains to describe the ethical and moral debate over how the advances are used. For many, embryonic stem cells are at the nexus of a political, religious and medical controversy.
If Scott's examination of stem-cell science helps to inform the ongoing debate, his look at possible treatments helps explain what is at stake. From reversing cancer to replacing damaged organs, much has been made of the generative aspect of stem cells. Stem Cell Now offers a sense of what is possible now, and what may come in the next decade.
Scott heads Stanford University's Program on Stem Cells and Society. He was also a founder and executive editor of the award-winning biotech journal Acumen. His writing has appeared in journals, including Science, Nature Biotechnology, and The Scientist.
Excerpt: Stem Cell Now
by Christopher Thomas Scott
Chapter 7
The Future of Medicine
"I want things to happen quickly. I certainly want to benefit within my lifetime. I don't want to get out of this wheelchair at the age of 75. I am 51, and am now very healthy, and would like to be out of the chair very soon. I'm not willing to resign myself to being an advocate for research that will benefit people only after I'm gone. I'm not that noble."
Christopher Reeve (1952–2004), in a 2003 interview
In the face of hard statistics, one wonders how modern medicine can help so much suffering. By 2010, over 2 million Americans are projected to contract end-stage renal disease, at an aggregate cost of $1 trillion. In 2001, nearly 80,000 people needed organ transplants, fewer than 24,000 got them, and 6,000 died waiting. Of those receiving organs, 40 percent die within the first three years after surgery. One in five of our elders 65 years old or older will require temporary or permanent organ repair or replacement during their remaining years. In 2002, the prevalence of diabetes in the United States exceeded 18 million people -- 6.3 percent of the population. That year, total heathcare costs of diabetes surpassed $130 billion. Cancer kills one out of four of us, more than 1,500 people a day. Even though we are living longer, many octogenarians are unable to appreciate their lengthy lives: nearly half of the people over age 85 have Alzheimer's disease. American lifestyles promote physical inactivity and overeating, causing morbid obesity, hypertension, and diabetes. Add to this list crippling conditions such as spinal injury, Parkinson's disease, multiple sclerosis, AIDS, and a host of genetic and metabolic disorders.
Heart disease is the biggest health crisis of all. In 2004, more than a million Americans died from cardiac failure and stroke, and heart disease leads deaths by all causes, outpacing cancer by 40 percent. No longer does it afflict only the old. Over 64 million Americans suffer from it, but only 25 million are 65 years or older. The total cost of treating cardiovascular diseases and stroke in the United States in 2004 is estimated to reach $368 billion.
Given an ever-widening chasm between treatment and morbidity, it is no wonder the stem cell has become a common denominator of hope. Behind the sobering facts, patients and their families ask, "Will there be a cure? And will it be in time for us?"
When?
Much of the promise of stem cells rests on a scheme for replacing parts worn out by age, injury, or infirmity. Unfortunately, the reality of stem cell biology is overshadowed by the hype. For example, the future is imagined to hold an inexhaustible source of stem cells with a perfect genetic match banked at a local hospital, available for your every medical whim. Need a new pancreas? Place your order, and three weeks later a new one lies ready and waiting in the surgical suite. Heart failure? No worries -- a few injections with multipotent stem cells will grow new cardiac tissue. And thus may 21st century patients extend their lives -- through a kind of patchwork medicine, held together by a fabulous, potent cell. This future sounds incredibly exciting. But it will take time -- and vision -- to us get there.
The truth of the matter is, we've got a goodly distance to go before regenerative medicine -- a catchall term for stem cell therapy -- will help large numbers of patients. It is very possible that many diseases will have to wait for cures from other quarters of medicine. Before any medical treatment (including cell and tissue transplants) is made available through hospitals or clinics, it must first be tested in humans through tightly regulated phases of clinical trials. The first phase determines safety and side effects in a few dozen subjects; the second phase tests efficacy in hundreds of patients; the third and subsequent phases try to prove statistical significance and confirm its effects in many hundreds or thousands of patients. The U.S. Food and Drug Administration (FDA) evaluates the data, and if the results pass muster, the product is approved for sale and moves to the market. Developing a new therapy goes slowly and is terribly expensive -- discovering, testing, and manufacturing one new drug can take between 10 and 15 years and cost nearly a billion dollars.
A hypothetical timeline of a new treatment for skin transplants might look like this:
• Basic Research: In 2006, a source of powerful adult stem cells is discovered beneath human skin. The rare cells are fingerprinted by genetic markers, and the markers are used to isolate the cells from the body and culture them in the lab. Over the next two years, technology is developed to grow the cells in quantity and used to change them into a variety of skin cell types.
• Preclinical Research: Different lines of skin stem cells and their progenitors are transplanted into the injured skin of a transgenic mouse with no immune system (to prevent rejection of the human cells). Over time the transplants are observed. One line works: the cells survive, go to the site of the injury, integrate into the skin, and heal the wound. Other kinds of animals are similarly tested. The tests take three years to complete.
• Clinical Research: The encouraging results in animals prompt tests in humans. In patients with severe burns, the patient's own skin stem cells are cultured, multiplied and then transplanted at the wound site. The cells improve blood flow, promote healing, and reduce scarring. Using adult stem cells is not the only way to approach the problem. An hESC line using nuclear transfer might also produce the skin stem cell in question. The technologies are further developed by companies, tested in more humans, and manufactured for use for burn victims. In 2014, the FDA approves the first cell therapy for use in clinics.
If the treatment being studied is for a disease with a genetic cause, another wrinkle must be ironed out. The faulty gene has to be corrected before the cells are reintroduced or the transplant could succumb with time, as did the original cells. This presents an added set of challenges to stem cell transplants. Once a genetically engineered stem cell is placed into the body and grafts into an organ, it may be there for life. If the change is in one of the wide-ranging cells of the blood or nervous system, the proteins made by the new gene will be everywhere in the body. Care must be taken to limit the effects of the therapy only to the affected areas.
How Much?
Customized treatments that can't rely on economies of scale are likely to be very expensive. For an adult stem cell regimen, the tissue in which the stem cells reside must be biopsied -- perhaps more than once -- surgeries that can put elderly patients at risk. For any cell therapy the methods for isolating, growing, and expanding the cultures must be perfected -- complications not yet perfected for adult stem cells. The procedures must produce millions upon millions of homogenous, long-lived cells that exhibit stemness. Like any transplant, the cells must be free of contamination with unwanted viral, bacterial, or chemical agents.
To avoid "homegrown" protocols and to ensure quality, companies and hospitals will need to standardize laboratory, manufacturing, and clinical practices. Health professionals will need training to provide proper informed consent and oversight of the procedures. Some researchers assert that for each patient, between 10 and 20 technicians will need to work full-time in specialized laboratories. The costs for such individualized treatments, they say, would be astronomical.
A different strategy may reduce the cost. Rather than developing a custom stem cell line for each person, nationwide banks of several thousand hESC lines could be developed. The banks would use a test called HLA (histocompatibility antigens) typing to match donor and recipient genes, minimizing tissue rejection. The closer the HLA match (either from family members or from outside donors), the less the chance that rejection will be a problem. A similar list of donors already exists. Over 6.5 million individuals have already been HLA-typed for bone marrow registries.
Other experts contend that individual treatments are feasible, and that once competition heats up, market forces will conspire to bring down prices. If a stem cell therapy can cure, they argue, then all the downstream costs of caring for chronic illness go away. A high initial price for injecting stem cells would be more than offset by future medical savings.
However, even with the concerns of time and money, there is plenty of good news. Stem cells are already used in clinics with resounding success. Here are the newest medical uses, some still in the last phases of preclinical development and some being tested in humans.
Healing Bad Blood
The tragedy of the Hiroshima and Nagasaki bombings showed how effectively radiation could obliterate the rapidly dividing cells of the marrow. Most radiation victims close to ground zero died within 30 days of exposure. Follow-up research found the only way to save mice from a dose of lethal irradiation was to transplant bone marrow from a healthy donor mouse. The results led others to wonder whether radiation and chemical agents could be used against a disease of rampant cell division, cancer. Their hunch was right, and by 1965 the first cure of childhood leukemia by a bone marrow transplant was announced. The researchers didn't know it at the time, but the marrow's rescue worker was the hematopoietic stem cell or HSC.
There are two basic kinds of bone marrow transplants. Extracting the patient's own healthy cells from the marrow, storing them, and putting them back later is called an autologous transplant. After the marrow is removed, doses of chemotherapy destroy both the cancerous cells and the bone marrow. The cells are then reintroduced to repopulate the marrow, thereby rescuing the patient. Autologous transplants are usually performed when the marrow is healthy and the cancer is elsewhere in the body. In the case of leukemias and multiple myeloma, the marrow itself is diseased. The marrow must be cleansed of cancer cells before it can be reintroduced. The advantage of autologous transplants is that the cells come from the patient's own body, so there is no rejection. New methods can sort the different cells in the bone marrow from each other -- similar in principle to the coin-sorting machines found in supermarkets. Clinical studies using blood stem cell purification techniques have found that patients are significantly less likely to have the cancer return and as a consequence live longer lives.
An allogeneic transplant uses bone marrow from a different person to treat the cancer. The donor's marrow is removed with a needle, treated, and filtered. Chemotherapy is administered to the patient, and the donor's marrow transplanted. Even the best cell filtration systems can't prevent the donor's immune cells from being transplanted and then attacking the patient -- in essence, a reverse kind of rejection. The sometimes-fatal side effect is called graft-versus-host disease (GVHD). Using HLA to select the best donor greatly reduces the severity of GVHD and cure rates have soared. The closest match usually comes from a family member such as a sibling. In these cases, immunosuppressant drugs are required to keep the patient from rejecting the donor's blood and the donor's immune cells from attacking the patient.
Stem cells are now used to treat patients who would otherwise have to rely on bone marrow transplants. Rather than drawing out bone marrow through a needle inserted multiple times into the hipbone, the procedure relies on the stem cells circulating in the donor's blood. To increase the numbers of HSCs for the transplant, two drugs are given to the donor. The first is a genetically engineered hormone called granulocyte colony stimulating factor (G-CSF). G-CSF causes the stem cells to expand their number, leave the bone marrow niche, and enter the circulation. Administering a second drug kills rapidly dividing progenitor cells and also increases the number of circulating HSCs. Like other bodily insults, the depletion of downstream cells creates a demand to regenerate the blood, prompting new stem cells to enter circulation. The blood is collected over the course of several days and filtered through a machine that isolates the circulating stem cells. Like a regular bone marrow transplant, chemotherapy or radiation therapy is used to kill the patient's cancerous cells and "empty" the bone marrow. The donor stem cells are transplanted and, if all goes well, travel through the blood to the vacant marrow where they colonize, produce red cells, immune cells, and platelets. Even with the bolstered numbers of stem cells, graft-versus-host-disease remains a complicating factor; rogue immune cells cause up to 20 percent of these procedures to fail. New purification techniques can help this problem, too. Removing the immune cells from the donor's HSCs can lessen the chance of GVHD.
Umbilical cord blood has emerged as a new source for transplanting blood stem cells to treat some malignant and nonmalignant blood diseases. Cord blood has only a few primitive blood stem cells because of the small volume of blood found inside -- a disadvantage when transplant success is tied to the number of cells infused. The small quantity means that such transplants are suitable only for children or small adults. Nevertheless, using cord blood has advantages. Tests of umbilical cord blood show that its stem cells are highly potent and very active, which means they generate more new blood cells in the bone marrow than their hematopoietic stem cell cousins. Because the immune cells in cord blood are quite immature, an exact HLA match is less important than it is in an HSC transplant using stem cells from an older donor. The incoming white blood cells are less likely to attack the patient, resulting in a lower incidence of graft-versus-host-disease. This increases the number of acceptable donors. To boost the numbers needed, mixed cord blood from several donors has been used with good success. As with other rare adult stem cells, the biggest barrier to using cord blood is their limited number and lack of methods to expand cultures to large enough quantities. Stem cell companies are working on methods to multiply cord blood stem cells so they can be used in adult patients.
Many parents donate their child's cord blood for public use. Like bone marrow registries, public banks need a wide variety of cord blood types in order to match donors with recipients. Parents with one sick child (or close relative who is sick) can bank the cord blood of a subsequent healthy child. Cord blood saved from healthy siblings has proven useful for helping children with genetic blood diseases such as sickle cell anemia, thalassemia, and leukemia. If the first child is affected with the disease, the cord blood from a healthy second child can be used as a transplant. At one such bank, Children's Hospital Research Center based in Oakland, California, 46 out of 55 children with blood disease were cured using sibling cord blood-matched transplants.
Should parents of a healthy newborn bank cord blood stem cells for possible use as future therapy for that same child? For fees and dues that run into thousands of dollars, profit-seeking cord blood companies encourage parents to store their baby's blood. The service is designed as a kind of biological insurance against future infirmities, such as leukemia, or for future use of the cells in regenerative medicine. If the family can afford the fees, a future cure for an unseen disease could well be worth the investment. There is some evidence that cord blood stem cells can make muscle and bone, but there is little evidence that they transdifferentiate. Cord blood may help patients with heart disease, too. In any case, it is likely that cord blood stem cells will be first to successfully treat anemias and other childhood blood disorders. For other diseases, families that want to bank their baby's blood will have to weigh the costs of keeping the blood against the likelihood that cures for diseases using cord blood stem cells will be found.
Protection from Rejection
How do immune cells "learn" to protect us? Why do immune cells betray us in diseases like rheumatoid arthritis and diabetes? The answers are found during early development. As our immune system matures, stem cells in the bone marrow develop into antibody-producing B cells, and progenitor cells move into the thymus, where they develop into T cells that protect us against foreign invaders. During fetal development, the immune system learns to distinguish between body cells that are "self" and foreign invaders that are "not self." What remains is a protective apparatus with astonishing flexibility.
Autoimmune diseases occur when the sufferer's body is attacked by its own white blood cells. They destroy cartilage (rheumatoid arthritis), nerves (multiple sclerosis) and organs (juvenile diabetes, Crohn's disease, and lupus). The current treatments only ameliorate the symptoms or slow the disease.
Transplants using embryonic stem cells could cure autoimmune disease, which is actually two problems: (1) a faulty immune system and (2) complications that arise from organs attacked by the immune system's white blood cells. Most of the time, transplants from one person to another cause a rejection of the host's tissue because it is recognized as "not self." In terms of curing autoimmune disease, the solution sounds too good to be true: a healthy immune system from an unrelated donor can replace a faulty one, and as a result won't attack the donor's organs or tissues. Stem cell transplantation experiments between mice have proved the concept. At Stanford University, Judy Shizuru and Irving Weissman treated one mouse with radiation, but at a low enough dose that didn't completely destroy the bone marrow. Before transplanting blood stem cells from an unrelated mouse, a purification step eliminated any stray immune cells from the donor that could attack the irradiated mouse and cause GVHD. The incoming stem cells grafted into the marrow, and the mouse recovered and began to manufacture two genetically distinct populations of immune cells -- the original ones, and the new variety from the donor. The immune cells that develop from the stem cells "learn" to recognize the recipient's cells as "self." After a period of time, the donor's stem cells take over the marrow and become the primary blood-forming system. Amazingly, these blood chimeras have a lifelong tolerance to any tissue transplanted from the donor mouse.
Human blood chimeras may prove to be the answer for genetically incompatible organ transplants of patients. A donor could supply a patient with a new, compatible immune system and an organ with little or no rejection. For more complicated autoimmune diseases the brass ring could come from human embryonic stem cells. Consider type I or juvenile diabetes, an autoimmune disorder introduced in Chapter 6. Diabetes is ruinous, destroying the insulin-producing cell of the pancreas. Complications from this type of diabetes include heart disease, kidney failure, nerve damage, and blindness. In order to cure type I diabetes, the faulty immune system and the damaged cells must be replaced. Using a line of hESCs made from the patient's own cells won't solve the problem, because immune cells made from the line will have the same defect.
A hypothetical multistep solution using a donor line of embryonic stem cells, shown on the next page, could help patients with diabetes and other autoimmune diseases. First, the patient's immune system must be partially destroyed with chemotherapy. This resets the immune system to the time before it incorrectly learned to attack the patient's own cells and organs. Then, a donor line of embryonic stem cells with a good HLA match would be created. The hESC line would be used to make a population of hematopoietic stem cells. After transplanting the HSCs into the patient, new immune and red blood cells are made. Later, new insulin-producing cells made from the same embryonic line would be transplanted to help repair the pancreas. The beauty of this method -- called co-transplantation -- is no rejection, because both the immune cells and the new pancreatic cells come from the same genetic source and are immunologically compatible. The method could work for other autoimmune disorders like multiple sclerosis: a donor line of embryonic cells could reset the blood system and provide new oligodendrocytes, the neural cells that make myelin, the nerve-conducting material.
Cell Therapies to Mend a Broken Heart
Cell therapy hopes to treat people with failing organs (such as the heart, lungs, and liver). Clinical trials using adult stem cells are underway. A Maryland company, Osiris Therapeutics, Inc., hopes its line of mesenchymal cells will prevent graft-vs-host disease after bone marrow transplants. Osiris also uses the cells to regenerate cartilage in injured and arthritic knees and is testing them in patients with heart disease. Building an organ like the heart from scratch is another matter, but stem cells can do the work in damaged areas, much like a road crew repairing a bad stretch of interstate (or inner-state) highway. To be effective therapeutically, stem cells must be made in sufficient quantity and must be shown to repair the organ. Most importantly, the repair must stand the test of time. Using stem cells to treat heart disease is an especially interesting case in point.
Donald Orlic, an associate investigator at the Genetics and Molecular Biology branch of the National Institutes of Health and his collaborators reported in 2001 that, in heart-injured mice, massive numbers of bone marrow cells repaired the damaged tissue. He interpreted the results as stem cell plasticity: blood stem cells changed into heart cells called cardiomyocytes. The desperate medical need and reasonably safe procedure of injecting heart patients with their own blood (containing hematopoietic stem cells) spurred a clinical trial in Brazil, and by 2003, ten trials in clinics around the world had enrolled hundreds of subjects with end-stage heart disease. Clinicians reported cases where formerly bedridden patients were jogging and climbing stairs after the procedure. In 2003, the British medical journal Lancet reported that patients receiving their own bone marrow enriched for stem cells had improved cardiac function and blood flow. The FDA reviewed the Brazilian and European data and moved to approve American trials in hospitals in Texas and Massachusetts in 2004 and in Maryland in 2005.
The foreign trials did show a modest (and statistically significant) improvement in heart function. The percentage volume of blood pumped out of damaged ventricles into the aorta increased up to 8.5 percent. In the meantime, two laboratories working independently at the University of Washington in Seattle and Stanford University could not repeat the Orlic lab experiments. The Stanford group injected highly purified populations of blood stem cells with a genetic tag into the heart muscle of 23 mice. The transplanted cells did not increase the survival rate in mice, did not persist in the heart muscle more than 30 days, and did not produce the signature proteins of heart cells (and instead continued to produce those of blood cells). The cells did, however, improve pumping efficiency slightly. Later, the Lancet published the first fully controlled, randomized, and blinded study using unpurified HSCs on heart patients. In 60 patients with myocardial infarction, the average improvement was 6.7 percent. Meanwhile, early reports from the Texas and Boston trials are encouraging. After the procedure, some bed-bound patients are said to be leading normal lives, but their long-term outlook remains unknown.
If sick people get better, then why even debate stem cell plasticity? In the emotionally charged arena of adult and embryonic stem cell research, some worry that the results will cause political winds to shift even further away from acknowledging the benefits of hESCs. To doctors treating sick people, the argument about plasticity isn't as important as the clinical result: what matters is whether the patient gets better. It could be that stem cells improve angiogenesis, the formation of blood vessels. In one recent instance, Advance Cell Technologies' Robert Lanza and his collaborators found that transplanting blood precursor cells found the developing embryos into the damaged hearts of mice repaired nearly 40% of the tissue within a month. Lanza's group found that not only did the cells rebuild the heart, the transplants helped the repaired tissue form a new system of arteries and capillaries. Or some other collateral effect might be at work. Because pure stem cells are not used, the effect could be due to something carried along in the mix of cells and liquid. The HSCs could be fusing with cardiac cells, and the union could promote healing. But fused cells do not divide, and so can't contribute to heart repair beyond their limited lifespan.
Some laboratory scientists say the clinicians moved too swiftly. Transplanting mixed populations of cells, they say, leaves the mechanisms of the therapy locked in a black box. Harvard's Amy Wagers worries about declaring victory too early. "If we consider a 6 percent improvement in cardiac function a success, then we've left behind an opportunity to understand why this is happening and aim for a 60 percent improvement." Stem cell hunter Kenneth Chien wrote in the April 8, 2004 issue of Nature, "we should be wary of prematurely pushing laboratory research into clinical practice." The Harvard scientist went on to say, "Now is the time to search for the presence of naturally occurring heart progenitor cells." And about a year later, he found them. In February 2005, Chien discovered a self-renewing population of stem cells in the hearts of adult rats.
Clinicians point out that all the studies were done safely, and that some patients fared better after the trials. Joshua Hare is a Johns Hopkins University cardiologist and one of the directors of the university's Institute for Cell Engineering. Hare is using mesenchymal stem cells to treat his heart patients in the Baltimore, Maryland clinical study. He points out that millions of dollars and years of effort can be spent trying to pin down the minutiae of stem cell science when patients need help immediately. "Basic scientists say it is premature to do the trials when the mechanisms are unknown," says Hare. "I say it's unethical to wait. We won't fully understand the mechanism until we do the human studies. That's what clinical research is all about!"
Bioconstruction Zone: Tissue Engineering
Stem cells are quietly revolutionizing a high-tech medical field that unites engineering, materials science, and cell biology. The two-decade-old field of tissue engineering relies on the body's own repair mechanisms. A "scaffold" made of nylon or a biomaterial like collagen is transplanted into the body. Cells use the scaffold as support, replacing it over time with natural three-dimensional tissue. Scaffolds can be used with transplanted cells too. Like the cells in bone marrow transplants, the introduced cells are either from the patient or from a donor.
The success of tissue regeneration varies from organ to organ. The lung, like the heart, has little regenerative oomph. Yet when stem cells from the human lung are purified and put onto synthetic polymer sheets, they form smooth and shiny pulmonary tissue. And mouse lung tissues made from stem cells develop into respiratory structures after transplantation. Pancreatic tissue hasn't been made, though insulin-producing cell systems are under intense study. The liver can regenerate easily in the body, but a reliable method of growing cells in the lab has not yet been found. Rudimentary skin grafts made using collagen and cell suspensions have helped burn patients for more than 20 years, but regenerating fully functioning skin that does not scar is still a distant goal. For most organs, the secrets lie in the pathways of stem cell differentiation. If science can discover the genes and proteins involved in every step of tissue and organ formation, it may be possible to precisely manufacture the necessary body parts.
Human embryonic stem cells can be used to make beating heart cells, but that is just a start: to be useful as a tissue graft, they must grow into organized structures. Seeding a scaffold made from a thin patch of biomaterial with heart muscle cells begins the regeneration process. Once such structures are sewed into mice, heart cells that secrete matrix-forming proteins infiltrate the patch. This stimulates the construction of blood vessels and eventually new myocardial tissue and muscles develop. The heartbeat stretches and strengthens the new tissue as the scaffold slowly degrades.
Making bits of the body's plumbing is proving easier. Like any transplant, the proof in the pudding is whether these stem cell-directed structures can function fully and survive for the lifetime of the patient. Several labs are focusing on forming blood vessels. Another group has devised a way to make a trachea, the thin tube that carries air to the lungs out of cells found in the nasal cavity. MIT researchers are teasing hESCs into cells that line the blood vessels. They seed them on scaffolds, sprinkle in growth compounds, and a few days later watch networks of small tubes traverse through the matrix. When transplanted into a mouse, the manufactured vessels incorporate into the mouse's vasculature.
The Organ Makers
The future of stem cell research has also come to the southeastern United States. Research Triangle Park, North Carolina is a busy amalgam of biology, technology, and commerce. Wake Forest is just one of several universities that ring the 7,000 acre park, and nestled among the rolling hills are dozens of companies dedicated to research, drug discovery, and healthcare services. Research Triangle Park is billed as the total package, where good ideas can flourish into products. Inside the medical school over an acre of glistening laboratory space is crammed with sleek laboratory benches, special microscopes, and incubators. And in one brightly lit room, tall cylinders of clear liquid bubble and boil, and grow entire organs.
What does it take to lure one of the world's best tissue engineers away from the heady environment of Harvard University to the tobacco country of North Carolina? A top research university like Harvard, with its medical center and affiliated teaching hospitals, has thousands of faculty members, employees, and graduate and medical students, millions of square feet of space, and billion dollar budgets rivaling many big corporations.
The answer is, quite a bit, actually. It took a multimillion-dollar recruitment package and the promise of a new institute in regenerative medicine for Wake Forest University, with its small but highly regarded medical school, to lure the slightly built and intense scientist away from Harvard's ivy halls. Anthony Atala, 46, belongs to a breed of restless surgeons found in the country's top teaching hospitals. He's confident that what he's created will help the people he treats. "I have one goal," the soft-spoken doctor of urology states flatly. "To cure the patient." Atala is among a growing cadre of physician-scientists who combine their knowledge of human anatomy with an understanding of engineering, electronics, drug development, and computing, to devise widgets that will propel us into a buzzing and whirring old age.
The Southeast's dedication to technology is another reason Atala and his team of scientists made the pilgrimage from Cambridge. "Everything we need is here. I can recruit the best scientists to an institution that encourages inventiveness. The local and state governments provide resources and land, and we have capital markets that invest in small companies," he says. In order to make tissues and organs to strict standards, the university gave him funds to build a government-certified facility to manufacture organs near the institute. The institute also has a venture fund, managed by Wake Forest, that invests in the most promising medical discoveries. Atala hopes that once his new ideas hit the market, the profits from products and public offerings will flow back and fund more research -- a virtuous cycle.
It's an interesting combination; the razzle-dazzle high finance of biotechnology linked to a man who believes that slow and steady will win the race. After years of experimentation, in 1999 Atala created the first human organ -- a bladder -- using tissue engineering. The bladder looked pretty normal -- oblong, hollow, with a narrow top and bottom -- and was complete with blood vessels, nerves, musculature, and openings in the right places. Other organs followed. Using a sample of human tissue, he's been able to make cell suspensions that form uteruses, vaginas, and large blood vessels. Believe it or not, Atala's group has constructed a fully functioning rabbit penis. Randy rabbits with newly engineered members chase their female counterparts around the cage barely four weeks after surgery. His laboratory equipment is mostly custom built. Fish-tank-sized structures connected to transparent hoses are controlled by a blizzard of dials and gauges. A handful of his new organs have already been transplanted into humans. Atala doesn't rush things -- he's still observing patients with manufactured bladders four years later and aims to try larger clinical trials only when he's certain he's found the safest and most efficient procedures.
Ten years ago, they said human organs couldn't be built. Now the challenge is unraveling the knotty problem of solid organs, like the liver, pancreas, heart, and lungs. Using renal tissue from cows and a spongy matrix no bigger than a 50-cent piece, the institute has made miniature kidneys that filter blood and eliminate straw-colored fluid. The surprising thing about many of these successes is that they don't rely on a pure source of stem cells. As long as the right kind of stem cell is in the mix of tissue, the brew of growth factors and scaffolds do the rest.
"Most of our research has a stem cell focus, both adult and embryonic," he maintains. "Some people are under the impression that regenerative medicine is this science-fiction drama with dozens of ready-made organs hanging in refrigerators, waiting for patients. That's nonsense." He waves his arm toward a collection of scientists and students huddled over an organ culture machine. "The reason that we've assembled an international group of physicians, engineers, and biologists is that one technology doesn't solve all problems. We have to change our expectations about regenerative medicine. The absolute first priority is the patient -- what's best for the patient?"
To illustrate, Atala recites a litany of broken and diseased human parts and the approach for each. "If a heart has an infarct [or damage]," he says, "engineering new tissue from embryonic stem cells is best, because trying to biopsy a bit of the heart in order to isolate cells for tissue engineering endangers the patient." The same goes for especially sensitive organs like the pancreas, where the slightest injury provokes pancreatitis, an inflammation that can destroy the organ. Atala flashes his frustration with conventional surgical wisdom. "Why is it that surgeons think that if a piece of your heart gives out, you have to change the whole heart? You don't! Our organs have tremendous reserves. When someone comes to a doctor with heart pains or kidney trouble, it's because 90 percent of the organ has failed. You don't need much repair to get back to a normal lifestyle. And a stem cell patch may be the best approach."
When asked about whether making customized organs and tissues patient-by-patient will be cost effective, Atala replies, "you can't argue with autologous." His point is that making organs from a patient's own cells is the best way to go, regardless of cost. He claims he can build a hollow organ in just five weeks: four weeks to expand the number of cells and one week to seed and build the "construct," the three-dimensional structure that becomes the organ. The advantage is no tissue rejection. Once again, Atala cuts to the chase: "Immunosuppressant drugs are nasty things. I think that people who suggest that we can control rejection with better HLA matches haven't spent much time at the bedside of someone on prednisone. There are too many immune genes that make us different, and more are discovered every year. I don't believe that we'll solve immune rejection in my lifetime, or perhaps ever."
So to get where he wants to go, Atala is focusing on how nature does it and what's best for the patient.
Repairing Nerves
The "before" videotape shows a rat with a recently damaged spinal cord. Staggering inside a circular Plexiglas container, the animal drags its hindquarters along the runway, its tail trailing limply behind. The next segment shows the same rat after an injection of oligodendrocytes made from a line of embryonic stem cells. It sniffs the air and stands on its rear legs. Dropping down, it takes a lap around the cage with only a slight suggestion of a limp -- once disabled, now cured. The revived rat is compelling visual evidence that Professor Hans Kierstead uses to wow audiences of scientists, patients, and news reporters. The University of Irvine neuroscientist is backed by the Christopher Reeve Foundation and the stem cell company Geron. His recently published research on rats has caused a stir among patient activists and physicians who are impatient for human testing to begin. He takes embryonic stem cells and differentiates them into pure colonies of oligodendrocytes, the neural cells that form the conductive material myelin. The cells are then injected seven days after the injury, and the rats began to walk properly within two months of the treatment. Timing is crucial: when Keirstead waits until 10 months after the injury, motor movements do not return. The rat's trauma doesn't sever the nerves -- leaving the basic wiring essentially intact -- and it's not clear how effective the procedure will be for injuries involving severed nerves or scar tissue. Geron hopes to clinically test the safety of their therapy in as early as 2006, during the routine surgery that follows an accident. Repairing damaged human nerves can be a major medical victory -- the success would ripple far beyond spinal injury to demyelinating diseases, such as multiple sclerosis.
Chapter 3 detailed the chain of developmental events that lead to the most complex network of cells in the body, the nervous system. When it comes to understanding how nerve cells come to be, Anders Bjorklund, professor and chief of the Wallenberg Neuroscience Center at Lund University, Sweden, says that "compared to our understanding of the blood stem cell system, we are at least a couple of decades behind." Bjorklund, with support from the Michael J. Fox Foundation, pursues clinical research in Parkinson's disease, where loss of cells that produce dopamine causes neurons to fire out of control; this results in loss of motor movements.
At this writing, no human clinical trials are using stem cells for Parkinson's, but there is a history of treating Parkinson's patients using neural cells from aborted fetal tissue. Bjorklund's ground breaking work in the late 1980s transplanted six-to eight-week-old neural fetal cells into the brains of humans and proved that cell therapy could actually work. In the majority of patients the injections improved motor function. Follow-up studies have been less encouraging. A clinical trial in 1999 at Columbia University and the University of Colorado had mixed results, helping younger patients but offering no benefit to patients over 60. In 2001, the same physicians did a follow-up study, but this time tremors in 6 out of 20 patients receiving fetal cells became worse. The results worried many who feared that cell therapy could be more damaging than therapeutic, especially when treating brain disease. As a result, preclinical work with stem cells is moving slowly through animal testing. Chapter 6 describes how embryonic stem cell therapy can improve Parkinson's-like symptoms in rodents and monkeys.
Slow-progressing brain diseases are heartbreaking, but there is an affliction that is even worse: Batten's disease. In Batten's patients, a defective enzyme keeps cells from degrading lipoproteins, fatty packages of cholesterol that travel through the bloodstream. Lipoproteins accumulate in the cell's cytoplasm to the point where they destroy neurons, retinal cells, and brain cells. The afflicted individuals go through rapid stages of blindness, ataxia, dementia, and finally, death. Batten's disease is fatal and affects only children. In the United States alone, 10,000 infants will appear healthy until their first birthday. By age three they will be dead.
Scientists at the biotech company Stem Cells Inc. believe they have an answer for Batten's patients. They hope their discovery will also lead to treatments for other lysozomal storage disorders like Gaucher and Tay Sach's disease. The researchers used stem cells found in the human brain to perfect a procedure that multiplies them into clusters of multipotent neural stem cells. After human cells are transplanted into a mouse with a disease that mimics Batten's, the stem cells travel to the damaged areas and begin to secrete normal enzymes, slowing the progress of the mouse's symptoms. Ann Tsukamoto, Stem Cell Inc.'s Vice President of Research and Development, is encouraged by the results. "The fact that we see increasing levels of enzyme production over time is very positive," she says. "It means that transplanted cells are renewing, multiplying, and might be replacing dead cells with normal neurons. We're hopeful that a single transplant may be enough to treat these patients." The company hopes to start human clinical trials sometime in 2006.
Stem Cells as Tools
The experts agree that immortal embryonic lines will become one of biology's most powerful tools. The Australian embryologist and stem cell biologist Alan Trounson, a pioneer of in vitro fertilization, believes that "studying disease with stem cells is incredibly important for research. We need to develop embryonic cell lines from patients who've got muscular dystrophy, Alzheimer's disease, and cystic fibrosis. That way we can develop drugs that actually block the disease from occurring." James Thomson agrees. "Human embryonic stem cell research will be developed more as a research tool than for transplanting engineered cells and tissues. I mean, think about disease for a minute," he says. "You don't want to do anything so crude as replacing those cells once they have died. You want to stop the disease from happening in the first place! If you had a reliable supply of neuronal cells, for example, you could study them to understand exactly how Alzheimer's disease causes them to die."
Discovering drugs is an important application of hESC technology. Potential drugs made of chemical or biological compounds can be tested in cultures of pure populations of cells that are specifically related to or affected by the disease. For example, the dopamine-producing neurons implicated in Parkinson's disease might be made from hESC lines and stored in quantity. Treating the neurons and measuring their response would quickly sort out which chemicals work best. Thousands of potential drugs tested in this fashion would speed up drug discovery. Existing pharmaceuticals could be refined and improved in the same fashion.
Gene therapy is a relatively recent and highly experimental approach to treating disease. Although most drugs are manufactured outside the body, gene therapy takes a different approach: a gene is delivered into the affected cells in the body, where it produces a protein that acts as a therapeutic agent. The potential success depends not only on the gene's delivery into the appropriate cells, but also on the gene's ability to function properly. Both requirements pose considerable technical challenges. Noninfectious viruses are used to deliver the gene, just like ordinary viruses infect cells. Unfortunately, this method is imprecise and also limited to the specific types of cells the virus can infect. If the proteins aren't produced efficiently or the transformed cells eventually die of old age, then repeated rounds of therapy are needed.
Gene therapy can be improved by using stem cells. Because stem cells self-renew, they can reduce the need for repeated rounds of therapy. Blood-forming stem cells are especially good choices for delivering drugs because they are easily removed from -- and reintroduced into -- the body, and once in the body they home in on certain organs and structures such as marrow, spleen, and thymus. Dozens of human clinical trials have used HSCs to deliver therapeutic agents such as interferon to patients suffering from blood and solid-tumor cancers (as opposed to cancers of the blood), anemias, and immune diseases such as SCID and HIV. In some cases the results have been promising, extending the lives of terminally ill patients. Cell-to-cell fusion -- one of the phenomena behind apparent stem cell plasticity -- might also be a way to deliver a therapeutic gene. If the disease is due to a missing or defective gene in the liver, an engineered blood stem cell might fuse with liver cells and produce the needed protein. However, fusion is a rare event, so delivering enough protein to repair the organ may be a problem.
Neuroscientist Anders Bjorklund believes that a combination of gene and stem cell therapy holds the key to correcting brain dysfunction. He's set his sights on a mutation in a gene implicated in Parkinson's called Nurr1. If a corrected copy of Nurr1 can be delivered to patients via stem cells, he believes it will slow or stop Parkinson's progression. The idea is to swap a corrected copy of the defective gene into an uncommitted neural cell. Many such engineered cells could be injected directly into the brain. If the cells took hold, they would manufacture the missing protein. Bjorklund adds that cells that promote brain healing and self-repair could be injected. The big hurdle here is navigating the pathways of cell differentiation. According to Bjorkund, "One of our dilemmas is that we don't always know what is, and what is not, a nervous system stem cell."
Experiments using other kinds of stem cells to carry therapeutic cargo are underway. High-powered mesenchymal cells carrying the cancer-fighting gene for interferon doubled the survival rates for transgenic mice ridden with human tumors. The cells homed in on tumors no matter their location, suggesting a way to treat human cancers that have already spread. Neural stem cells carrying antitumor agents such as interleukin 2 also show promise. In mice with brain tumors, the stem cells produce and release interleukin 2, which then stimulates white blood cells to enter and kill the cancer cells. Other neural stem cells deliver the drug right to the cancer cells themselves, ensuring a good kill rate.
Stem cells are being used to diagnose disease. At a growing number of in vitro fertilization clinics, single-gene defects that cause Huntington's, Tay Sachs, sickle cell anemia, cystic fibrosis, and dozens of other disorders are being detected via an embryo-sampling technique called preimplantation genetic diagnosis, or PGD. Four days after fertilization, while still in a laboratory dish, an eight-cell embryo is grasped gently by light suction and a single cell is removed with a pipette. The embryo recovers with a quick round of cell division. The DNA in the cell is extracted and then tested with a genetic probe for the disease in question. The test ascertains whether the embryo has no disease genes, is a "carrier" with one disease gene and one normal gene, or has both copies of the gene and will therefore develop the disease. Only embryos with no disease genes are chosen for implantation. Parents who carry the gene, or who have family histories of the disease, can use PGD to avoid having an affected child. A separate analysis identifies a group of different diseases caused by the wrong chromosome number, such as Down's syndrome, or abnormalities that lead to miscarriage. PGD has emerged as a tool for parents whose only other option would be to test abnormalities during fetal development. In most cases, PGD enables the family to avoid the difficult decision of whether or not to end a late stage pregnancy. The procedure is expensive, running $5,000 for both sets of tests.
Just as advances in reproductive biology helped embryologists derive the first human embryonic stem cell lines, PGD can help study disease. Rather than discarding donated embryos that test positive for defects, a clinic at the Reproductive Genetics Institute in Chicago has developed over 30 hESC lines by transferring the defective nucleus into enucleated eggs. These stem cell lines, each with a different genetic disease, are now available to researchers who can use them as an in vitro model. Observing how these cells behave compared to normal cells will help identify how certain diseases begin, progress, and affect healthy tissue. Not only are the disease-causing genes and their proteins identified, this also opens up possibilities for designing drugs that reverse or treat the problem.
The story of Molly Nash illustrates how stem cell tools and therapies can work together to save lives. The Colorado child was born with Fanconi's anemia, a genetic blood disease with an especially poor prognosis. Most patients rarely reach adulthood and die of leukemia. A bone marrow transplant from a healthy sibling with a matched HLA or immune profile can cure the disease, but Molly was an only child and her parents -- both carriers of the deadly gene -- were fearful of having another child with the disease. They used in vitro fertilization, pre-implantation diagnosis and a cord blood transplant in an attempt to save their child. PGD was used to screen 24 embryos made in the laboratory. One embryo was disease-free and matched Molly's immune profile. The blastocyst was implanted and nine months later her sibling, named Adam, was born. The stem cells from Adam's umbilical cord were given to Molly and today she is eleven years old and free from disease.
The diversity of stem cell treatments reflects the diversity of stem cell breeds. Lines of hESCs may become the preferred source of cells used to treat patients. Presently, tissue engineering, bone marrow transplants and the results from early clinical trials confirm the utility of adult stem cells taken from the body. Along ethical dimensions, the two kinds of cells are very different, and those differences deserve a closer look.
Excerpted from ' Stem Cell Now' by Christopher Thomas Scott. Copyright (c) 2006 by Christopher Thomas Scott. Excerpted by permission of Pi Press, a division of Penguin Books.
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