American attitudes to stem-cell therapies are changing fast
Can I serve you now?
FOR the past eight years, America’s government has declined to fund new research into one of the world’s most promising medical technologies: the use of human embryonic stem cells to repair or replace damaged tissue in the diseased and injured. Embryonic stem cells are special for two reasons, one scientific and one ethical. The scientific reason is that they are able to turn into any of the body’s myriad cell types, which is why they might be used in this way. The ethical reason is that, at the moment, harvesting them usually involves killing human embryos. The embryos in question have no future anyway (they are usually “spares” from in vitro fertilisation procedures). But it was this destruction of potential human life that disturbed George Bush and his supporters.
Barack Obama has promised to reverse the ban. When that happens, American academics will no longer have to watch enviously from the sidelines as their colleagues in Australia, Britain, China, the Czech Republic, Israel, Singapore and South Korea push ahead. But though the legislative wheels have yet to start turning, the mood has already shifted.
One sign of this shift came on January 23rd when the country’s Food and Drug Administration (FDA) granted permission for the first clinical trial of a therapy based on human embryonic stem cells to Geron, a firm based in Menlo Park, California. Geron was able to ask for permission, and the FDA was able to grant it, because the ban does not apply to privately financed research. America, it seems, is back in the stem-cell business.
Off we go
Geron’s trial is of a treatment for paralysis caused by damage to the spinal cord. Between eight and ten patients with severe spinal-cord injuries will be recruited to test this treatment for safety. At the same time both the researchers and the patients will be looking for signs of improvement in the condition. If the trial is successful, larger ones will follow.
The trick that Geron’s researchers have learned is how to turn embryonic stem cells into cells called oligodendrocytes. These, in turn, generate a structure called the myelin sheath, which insulates nerves against leakage of the electrical signals that carry their messages around. Geron plans to inject its oligodendrocytes into the damaged spines of patients between one and two weeks after their injury.
Tests in rats, using human cells, have shown that oligodendrocytes injected this way can indeed help repair myelin sheaths and restore the ability of nerve cells to carry signals. The hope is that the same will happen in people. The nerve cells themselves will not be replaced, so even in principle such treatment could not help everyone with a spinal injury. Many observers do, however, see this research as a step along the road to reconnecting the brains and limbs of those with severed spinal cords, by growing new nerve cells to bridge the gap.
All new medical procedures need to be tested for safety, of course. With stem cells, the main risk is not the sort of chemical toxicity associated with a drug; rather it is of an unusual type of tumour called a teratoma. Teratomas are more or less normal bodily structures—eyes or teeth, for example—that are growing in the wrong place. They are a special risk with stem cells precisely because such cells can turn into any other sort. If the wrong genetic switch is flicked, the wrong sort of tissue results.
Another risk, though, is immune rejection. Introducing stem cells into a body is a bit like transplanting an organ: the recipient’s immune system might throw a wobbly and try to destroy the intruder. Geron’s patients will therefore have to spend two months taking anti-rejection drugs. Other people, though, think they may be able to get round this difficulty. The International Stem Cell Corporation (ISCo), in Oceanside, California, for one, reckons it can do so and, at the same time, deal with the ethical issue of embryo destruction.
ISCo has found a way of producing embryonic-like stem cells from unfertilised eggs. The egg is chemically stimulated to create a group of cells that form a non-viable (and unfertilised) “embryo”. This, explains Kenneth Aldrich, the firm’s boss, is something that could not be implanted into a woman’s womb and produce a child. Nonetheless, the cells it contains have the same characteristics as stem cells.
Besides any ethical advantages this procedure may have, it could also have medical ones. Because lines of stem cells created in this way have only one parent, they are immunologically simpler than normal embryonic cells—in other words they have a smaller variety of the proteins that trigger rejection. That lack of variety, says Dr Aldrich, means it might be feasible to create a bank of stem-cell lines that could be matched to every immune type in the human population, rather as a blood bank carries blood of all the different groups (A, B, O and so on). Replacement stem cells might then be ordered off the shelf.
Nor are spinal-cord injuries the only condition lined up for treatment. Both ISCo and Advanced Cell Technology, of Los Angeles, are trying to create stem cells that could stop—and possibly reverse—a process called macular degeneration, which leads to blindness. ISCo says it hopes to start human trials later this year. Using embryonic stem cells in this way is regarded as a particularly promising route because a similar form of treatment that employs stem cells recovered from still-born children is already known to work.
Try, try, try again
The true potential of this approach is unknowable. It might yet prove too difficult to use as widely as its supporters hope. Stem-cell therapy has been suggested as a way of dealing with arthritis, angina and Parkinson’s disease, as well as spinal-cord injury and blindness—a range of conditions that makes it look like a panacea. That risks disappointment and overreaction if things go wrong. But the only way to find out is to try.
Michael West, the founder of Geron and now head of BioTime, another biotechnology company, says the existing legislation has affected privately financed research as well as the public sort. Investors have been frightened off by the political debate. Once it is gone, the full brunt of America’s innovative know-how, academic and private, could transform the subject, as other countries may soon find out.
From The Economist print edition