Medics have a name for the devastating injury that Christopher Reeve suffered during what was supposed to be just another day's riding in May 1995. They call it the Hangman's fracture, after those best known to have exploited its swift and almost guaranteed effect.
When Reeve fell, he landed in such a way that his neck fractured high up, between the first and second vertebrae. It is one of the body's key weak points: sever the spinal cord so high up and not only does it stop nerve signals sparking between your brain and limbs, rendering you quadriplegic, it also cuts off nerve signals to your lungs. Without immediate attention, the Hangman's fracture causes death by suffocation.
With luck, Reeve got help immediately, and at that point began his public transformation from superhero to a man half-reclined in a motorised wheelchair.
But there was more to Reeve's transformation than the new limitations so visibly thrust upon him. He became a vocal advocate for the cutting-edge medical science of stem cell research. In stem cells, Reeve saw a powerful tool being hampered by US policy, a tool that not only promised potential therapies to heal himself, but to treat a host of medical conditions in others. "He wanted every effort to be made on behalf of patients of all disorders that could potentially be helped by stem cell research," says Roger Pederson, an acquaintance of Reeve's and professor of regenerative medicine at Cambridge University.
And Reeve made a difference. He campaigned in Congress. He was the public figure that brought the stem cell debate to the public. "He was the human voice that changed attitudes," says Colin Blakemore, chief executive of the Medical Research Council. "It's one thing for scientists to say, 'We know we can do this', but Christopher Reeve put all this into a real-life perspective."
Reeve came to the stem-cell debate when the US was considering outlawing therapeutic cloning, a technique where stem cells are harvested from surplus fertilised eggs created in fertility clinics. Such embryonic stem cells, it is thought, can be turned into any of the hundreds of cell types in the body. To its supporters, few medical technologies have held more promise, as they could potentially be used to replace damaged and diseased cells anywhere in the body. To its critics - and in Washington, that meant many Republicans and the religious right - this creation of embryos is morally repugnant.
Reeve saw the resistance as a challenge. "His dream was to come to the UK, be treated with a whole repertoire of stem cell therapies - that is to say, making nerves from stem cells through therapeutic cloning. He then wanted to return to the US and walk off the plane and be arrested for having infringed US laws against therapeutic cloning," says Pederson.
With an eye on the electorate, the Bush administration imposed strict controls on therapeutic cloning, declaring that while private institutions could do whatever they wanted, federal funds could only be used to research stem cells created before 2001. Without the full weight of federal funding behind it, Reeve and many scientists felt stem cell research had been scuppered. He set up the Christopher Reeve Paralysis Foundation to fund some of the best research into therapies for paralysis, but research is an expensive business and the $15m (£8.3m) a year the foundation dedicated to research was just a fraction the US National Institutes of Health could have paid for, if the Bush administration had allowed it. "He was incensed by the quitter attitude of the Bush administration, which held back from exploring every possible avenue," says Pederson.
Despite the restrictions in the US, which presidential candidate John Kerry has vowed to lift should the US electorate give him the chance, stem cell research continues at a fierce pace. Last year, the California-based company Geron announced they had used an injection of human embryonic stem cells to restore some function to rats who had had their spinal cords cut. The work, though promising, is still a lab study. In the real world, fractures are messy and when nerves are damaged in the spine, the injury site is quickly mobbed with cells that make nerve repair extremely difficult.
Geron is arguably the world leader in trying to use stem cells to treat spinal cord injuries. But in other companies and universities, stem cells are being put through their paces to see if they can help treat conditions as disparate as Parkinson's, Alzheimers, diabetes and motor neurone disease. Others are using stem cells to correct irregular heart beats and salvage damaged retinas.
In Britain, one of just a handful of countries to have firm legislation allowing therapeutic cloning to produce stem cells, only one licence has been granted for such research. Based at Newcastle University, Miodrag Stojkovich and Alison Murdoch of the Newcastle Fertility Centre hope to produce stem cells to study diabetes and Reeve's contribution to helping the public understand the merits of stem research is not lost on them. "We will miss his contribution, especially where mediation of scientific progress to the public is needed, but we hope that we will go on where his dream stopped," says Stojkovich.
Last month, Ian Wilmut, the scientist behind the team that cloned Dolly the sheep, applied for a licence to clone embryos to make stem cells, this time to treat motor neurone disease. If their application gets the green light from the Human Fertility and Embryology Authority, the body that polices such research in the UK, the team hope to begin work by Easter next year.
If ever there were a flurry of activity in medical science, stem cells has to be it. In one week this month, two scientific teams reported successes with stem cells. In Israel, Izhak Kehat of the Technion-Israel Institute of Technology created biological pacemakers for pigs, by implanting heart cells derived from human stem cells into their hearts. If the technique works in humans, it could make electrical pacemakers obsolete. Meanwhile the Massachusetts-based Advanced Cell Technology announced they had, for the first time, transformed stem cells into retinal cells. Transplanted into the eye, the company hopes that the cells could reverse some of the most common forms of blindness.
Within the stem cell community, arguments still rage over whether funding should be skewed in favour of more versatile embryonic stem cells or the less ethically problematic adult stem cells. These provoke less ethical backlash because they can be extracted from people who are able to give consent. Bone marrow has long been known as a rich source of adult stem cells, and they are also found at the base of hair follicles, where they help stimulate hair growth. But scientists believe adult stem cells have a downside - they cannot be transformed into any kind of cell. Their role in the body has already, at least in part, been determined. More versatile may be stem cells taken from the blood of umbilical cords, though again, these have limits on what they can turn into.
The balance of versatility versus acceptability is very different for embryonic stem cells. While scientists believe that these cells can truly form any other type in the body, that they must be extracted from a ball of 100 or so cells grown from a fertilised egg is viewed by some as morally objectionable.
Many who have staked their futures on finding cures with stem cells are reluctant to say when real therapies will emerge, so when Reeve announced his desire to walk again, so soon after his accident, many saw it as the most wishful of thinking. According to Pederson, though, his hopes were not misplaced. "It's probably 10 years off and that's the tragedy, that it hasn't happened in Christopher's lifetime. Now we must redouble our efforts to make sure these advances happen in the lifetime of people who need them and can benefit from them."
