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Biomedicine

The Troubled Hunt for the Ultimate Cell

Capturing the human embronic stem cell might change the face of medicine. But to get there, a small band of researchers and biotech firms must endure a federal funding ban and ethical controversy.

John Gearhart’s lab is closed to outsiders.

Rather than happening there, an interview brokered by a university public affairs officer takes place in a windowless lecture room in the bowels of the Johns Hopkins University School of Medicine. Outside, seedy east Baltimore vibrates with the energy of a bright spring day. Gearhart appears and takes a seat under the fluorescent lights. Time is short, and no tape recorders, please.

With reddish blond hair and a direct gaze, Gearhart speaks with excitement about the vast medical potential of the research going on in his lab. He describes the early stages of human life and an elusive cell found only in embryos. But there’s much about this conversation that’s fleeting, incomplete and evasive. Suddenly his voice turns defiant and he’s scowling deeply. He relates how he and his family have received threats, how other scientists have criticized his failure to publish and his close ties with industry. And then he is gone, sprung by the clock-conscious PR man.

If awards were given for the most intriguing, controversial, underfunded and hush-hush of scientific pursuits, the search for the human embryonic stem (ES) cell would likely sweep the categories. It’s a hunt for the tabula rasa of human cells-a cell that has the potential to give rise to any of the myriad of cell types found in the body. If this mysterious creature could be captured and grown in the lab, it might change the face of medicine, promising, among other remarkable options, the ability to grow replacement human tissue at will. The ES cell could, scientists hope, be a factory-in-a-dish that turns out cardiac muscles to patch heart attack victims, neurons to mend paralysis or pancreatic cells to battle diabetes. “It’s a treasure house of opportunity for developing fundamental knowledge and medical applications,” says Michael McClure, chief of the National Institute of Child Health and Human Development’s Reproductive Sciences Branch in Bethesda, Md.

That all sounds so promising. Why, then, is John Gearhart besieged? The answer is that these cells are found only in embryos or very immature fetuses, and pro-life forces have targeted the researchers who are hunting for ES cells, hoping to stop their science cold. In addition, the federal government has barred federal dollars for human embryo research, pushing it out of the mainstream of developmental biology. To make matters worse, human ES cells could conceivably provide a vehicle for the genetic engineering of people, and the ethical dilemmas surrounding human cloning threaten to spill over onto this field. Deprived of the federal funds that power most basic biomedical research and surrounded by fierce controversy, the hunt for the ES cell is being undertaken only “by a few brave souls,” says Colin Stewart, a colleague of McClure’s at the National Institutes of Health (NIH).

Extensive reporting by TR suggests that in the United States, those brave souls are drawn from fewer than a half-dozen research groups. There are also a few others in the United Kingdom, Australia and Singapore. Even this intensive survey may have missed some researchers, since some probably prefer to do their work in silence. “We’re constantly wondering what our competitors are doing, and even who they are,” says Gearhart, director of research at the Johns Hopkins department of gynecology and obstetrics.

Taming the human ES cell wouldn’t just be a huge scientific coup-it would also be a potential gold mine for the biotech firm that took out an enforceable patent on the tabula rasa cell. But the same secrecy and controversy that dogs the researchers has also limited the open involvement of industry. Just one company is openly chasing the human ES cell-Geron of Menlo Park, Calif. This young Silicon Valley firm has aggressively signed collaborations with leading ES researchers, including Gearhart and Roger Pedersen, a reproductive biologist at the University of California, San Francisco (UCSF). A search of the U.S. patent filings also shows that a small startup in White Plains, N. Y., called Plurion, is building up intellectual property around the ES cell. But Plurion executive Mark Germain declines to comment further.

“It’s a taboo area,” says Doros Platika, CEO of the Cambridge, Mass.-based startup Ontogeny, a rising star in the developmental biology business. “Big pharmaceutical companies are afraid to touch it. And the field needs to sort itself out before we’d get into it.”

In spite of all these difficulties, there is a healthy scientific competition to catch the human ES cell-driven both by the desire for scientific glory and by the riches that might come with controlling the fabled stem cell itself. “It’s a race. I lose sleep,” Gearhart says. And despite many technical difficulties, several labs-including Gearhart’s-believe they may already have captured the ES cell and are working to characterize and control the cells, furiously filing patent applications as they go.

Furious scientific competition, threats of violence, huge medical potential, fear and secrecy. Welcome, behind closed doors, to the topsy-turvy world of the human embryonic stem cell.

A Breakthrough

The prize in this hunt is an invisibly small translucent dot found on the inside of an early stage of the human embryo, known as the blastocyst. Several days following fertilization, the blastocyst, a hollow ball of about 140 cells, rolls out of the fallopian tube and into the uterus, to be implanted there. Clinging to the inside of this rolling sphere are a group of identical cells-the ES cells-which are the starting point of the fetus. Soon they will divide rapidly and their descendants will take on increasingly specialized roles, emerging as heart, muscle, blood, bone, hair, nerves and all the rest of the human apparatus. For now, though, they are pure potential: holding the capacity to become any part of the body. And therein lies their mystery and their biomedical significance.

Biologists, understandably, are fascinated. But before they can study this primordial cell, they need to capture it-and control its growth-in the laboratory, something that hasn’t proved easy to do. Like physicists studying particles present at the birth of the universe by recreating its initial conditions in high-energy colliders, biologists are attempting to isolate the ES cell with a concoction of powerful biological substances that mimic those present in the first days of life.

The science behind ES cells began in earnest in 1981, when researchers in Great Britain and California independently succeeded in isolating a curious kind of cell from the interior of the mouse blastocyst. These embryonic cells were identical but each had the potential to give rise to an enormous range of different cell types-a defining mark of a stem cell.

Into the Fire

Back in Baltimore, Gearhart had adopted a radically different strategy-and one that appears to have propelled him to the front of the pack. He decided to sidestep the use of blastocyst-stage embryos altogether as a source of ES cells. The deciding factors were both political and scientific. The government’s funding ban, combined with the poor quality of available embryos “turned me away from that approach,” he says.

Instead, Gearhart picked up on a technique devised by cell biologist Brigid Hogan at Vanderbilt University Medical School. In 1992, Hogan showed that so-called primordial germ cells from the genital ridge (terrain destined to develop into the testes or the ovaries) of a mouse fetus could be grown in culture and acted much like ES cells. She hypothesized that the same approach might work in humans. Using aborted fetuses donated by patients, Hogan managed to isolate some interesting cells but wasn’t able to establish permanent cell lineages growing in culture-a key aim of ES research.

This alternative approach circumvented some of the funding and scientific difficulties of working with embryos. Yet in some ways it was a case of jumping out of the frying pan into the fire, since researchers using aborted fetuses are exposed to the same risk of violence from anti-abortion activists that abortion clinics face. “The threat to people working with fetal material is very real,” says Hogan.

Nevertheless, Gearhart took this strategy and ran with it-possibly all the way to the finish line. In July 1997, at the 13th International Congress of Developmental Biology in Snowbird, Utah, which was still abuzz from Ian Wilmut’s announcement that February that he had cloned a sheep named Dolly, Gearhart told a special ethics forum that he and postdoc Michael Shamblott had been growing “ES-like cells” in their lab for the preceding six months.

The connection between the ES cells and Dolly was more than just a coincidence of timing: Human ES cells could, in principle, be the vehicle for creating new breeds of human beings, as the mouse ES cells have already been used for mice. Gearhart, however, assured some attendees that neither he nor his colleagues had any intention of producing genetically altered people. His focus, he said, is strictly on the cells’ potential for saving lives by growing replacement tissues and organs and by providing important tissues for medical research. Yet even Gearhart’s colleagues understand where the fear of this new technology comes from. “It’s so easy to imagine the bad applications, since the misuse of technology, the Frankenstein myth, is already part of the vernacular,” says Pedersen, who chaired the ethics session at Snowbird.

Is Gearhart the winner in the race for the human ES cell? That’s not an easy question to answer. He and his collaborators say they have succeeded in growing “ES-like cells” from 5-to-9-week-old fetuses and are sustaining them in cell culture. But, in keeping with the field’s atmosphere of secrecy, Gearhart’s lab hasn’t yet published its results. The difference between these fetal germ cells and ES cells may well turn out to be a bone of contention among labs in the race. Gearhart, for his part, remains confident. “For all practical purposes,” he believes, these cells and ES cells will turn out to be “equivalent.”

Whether Gearhart has already won the race behind closed doors or not, the benefits for medicine of having a winner will be very large, with the largest payoff probably coming in the area of growing replacement tissues and cells.

Thomas Okarma, director of Geron’s cell therapy programs, says replacement tissues for transplant will likely be the “big hit” for human ES cells. The first type of transplantable cell Geron hopes to make are heart cells. Okarma imagines inserting a “cassette” of genetic instructions into an ES cell that would direct it to turn down the differentiation path to heart tissue. “The cells could be injected directly into the failing part of the heart,” Okarma says. The result could shore up failing heart tissue, nursing heart-attack victims back to health or providing a stop-gap for patients waiting for the right heart for a transplant.

Although Okarma envisions “a fermenter full of cells” derived from ES cells that someday will pump out new heart tissue, he stresses that the research is at an extremely early stage. To give some sense of how early, he tells TR that he hopes that within three years Geron will be testing the heart-tissue approach, using ES cells from Rhesus monkeys transplanted into other monkeys.

But the benefits of identifying and cultivating the ES cells are not only practical; there will be substantial rewards for science as well. “In theory,” says Okarma, “we should be able to generate an infinite and stable supply of [normal] human cells.” In addition to their clear medical uses, these cells, which could be turned into particular types of tissues at will in the laboratory, would be hugely useful in research. Liver cells might be used to study drug metabolism and toxicity, while other cell types might be used to test the efficacy of drug candidates. A combination of ES cell and genetic engineering techniques could also generate many interesting cell lines. Just one example: brain neurons that quickly develop the type of amyloid plaque associated with Alzheimer’s disease, providing an invaluable system for testing potential drugs to treat the ailment.

The ES cell could also open an invaluable window on human development, partly because developmental biologists would like to know which genes tell an ES cell to differentiate into more specialized cells. The proteins coded for by such genes could turn out to be new targets for drugs, or in fact be used as drugs themselves to spur, say, the regeneration of worn-out cartilage, or even to grow back receding hair.

Although the scientists at Geron are optimistic that they will be able to deliver on these promises, not everyone shares that upbeat state of mind. In spite of the apparent recent progress, some researchers who have worked with embryonic human cells doubt biologists will learn to control their growth anytime soon. H. Ralph Snodgrass, former chief scientific officer at Geron’s Menlo Park neighbor Progenitor, says, “It’s one thing to say the cells have the capacity to differentiate into all these cell types; it’s quite another to exploit that. There are some significant hurdles.”

Snodgrass is in a position to understand the practical difficulties. In the early 1990s, Progenitor, a biotech firm that also specializes in developmental biology, worked with human blastocysts, hot on the trail of the ES cell’s close cousin-an undifferentiated version of the hematopoietic stem cell (which gives rise to the full complement of cells in human blood). But Snodgrass recalls that Progenitor’s scientists couldn’t control the embryonic cell on anything other than an experimental scale-developing an actual therapy that could withstand the scrutiny of the Food and Drug Administration seemed out of the question. Progenitor has largely dropped that effort, and now focuses on better understanding the genes that control the development process in mouse embryos.

Even those who aren’t quite as skeptical as Snodgrass point out that there may be an easier route to finding a cell that could be useful as a source of replacement tissue. The shortcut involves stem cells that have already changed into a cell family, say bone or nerve, but have not yet given rise to a specific type of cell. These stem cells are a step further down the differentiation tree from the embryonic stem cell. And many scientists believe they could be far easier to isolate (partly because they are still present in adults) and nearly as useful as a source of tissue for therapies involving replacement tissues.

With so many uncertainties and questions remaining, no one is ready to declare the race for the human ES cell over or predict the winner. And it could take years to sort out the competition. Proving one has the ES cell, or even an “ES-like” cell, is no easy task since no one is exactly sure what it should look like.

According to James Robl, a biologist at the University of Massachusetts who recently saw presentations from several ES research groups at a meeting in Australia, “The cells that I have seen don’t look pretty, and they don’t look like ES cells. But we’ll just have to wait and see.” Gearhart,

But the ultimate test of an ES cell’s power, says Gearhart, “won’t be done.” As in mice, that ultimate proof involves implanting human ES cells in a developing embryo, producing a germ-line chimera: a person that could pass the traits of the implanted ES cell to its own offspring. Deprived of this ultimate assay, which lies far outside the bounds of what’s ethical or even feasible, it will be impossible to meet the strictest definition of an ES cell. But, when Gearhart looks at the composite picture provided by the other tests, he says, “We’re convinced.”

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