For all the past week's headlines about embryonic stem cells' medical promise there is a sobering reality: The science to prove that promise will take years, probably too long for many of today's seriously ill.
On his desk at Children's Hospital Boston, Harvard stem cell researcher Dr. George Daley keeps a file about 3 inches thick of e-mails and letters from patients and families who hope his work could help them. They are both inspiration and caution.
"It took much of the 20th century to figure out how to deliver chemicals as drugs," noted Daley. "We should be humble and appreciate it may take us the better part of this century to truly harness the power of cells as medicines."
Nor is there any way to know which kinds of cells ultimately will work — embryo-derived ones that elicit heated moral debate, or some of the many other types of stem cells that scientists are studying furiously.
President Barack Obama last week lifted restrictions on taxpayer funding of research using human embryonic stem cells, widening the field. The Bush administration had limited taxpayer money for that research to a small number of stem cell "lines," or groups that were created before Aug. 9, 2001, lines that in many cases had drawbacks that limited their potential use.
Make no mistake: Federal law forbids taxpayer money from being used to create or destroy embryos, and only Congress could change that, considered unlikely.
The National Institutes of Health now is developing guidelines on what kinds of stem cell studies will be allowed. The rules are due in July.
It's a young science to be so contentious. University of Wisconsin scientists culled the first human embryonic stem cells — from an embryo no bigger than the period at the end of this sentence — a mere decade ago. They're prized because they can turn into any cell of the body. If scientists could control that metamorphosis, they might create replacement tissue to treat a variety of diseases and conditions, from diabetes to Parkinson's to the paralysis of spinal cord injury.
But that initial culling of the cells does kill the days-old embryo. So critics say using the resulting stem cells — which can propagate in lab dishes indefinitely — makes taxpayers who are morally opposed to embryo research complicit in it.
There are various alternatives. Different types of stem cells can come from fetuses and placenta, blood and bone marrow. So-called "adult" stem cells that already have matured to create a given tissue-type aren't considered as flexible as embryonic ones, although some recently discovered in men's testicles seem close.
Then there are recently developed "reprogrammed" stem cells where scientists take, say, an ordinary skin cell and slip genes inside it to turn back the clock and make it embryonic-like again. If those so-called iPS cells truly prove to be as flexible as they appear, they could remove the moral debate — and even leading embryonic stem cell scientists hope that happens.
Meanwhile, critics argue that adult stem cells already can cure people. Indeed, what people once called "bone-marrow transplants" are injections of stem cells destined to grow blood and immune-system cells, and they do treat various blood and immune disorders.
But taking a stem cell destined to produce blood and making it grow heart muscle or nerves instead is very different, stressed Dr. John Gearhart of the University of Pennsylvania.
Adult stem cell injections temporarily helped heart-failure patients a few years ago. The new cells didn't grow but for a few months secreted substances that helped what was left of the old scarred heart tissue work a little better, he said. New attempts using different stem cells are under way now.
Spinal cord injury may be more amenable to stem cell therapy than diseases that could overtake and damage newly implanted cells. Stem cells have helped paralyzed rodents move again by repairing insulation lost around damaged nerves. In the first attempt at an embryonic stem cell therapy this summer, Geron Corp. will test if a few recently paralyzed people react similarly.
Last week another California company, DaVinci Biosciences, reported injecting a few paralyzed patients in Ecuador with stem cells from their own bone marrow. The researchers reported no side effects and recorded some signs of improvement in movement and bladder function two years later, although there was no way to know if that was due to the stem cells.
Scientists long thought Type 1 diabetes might be the easiest disease for stem cells to tackle. After all, some patients today do well with transplants of donated insulin-producing cells. But Gearhart said it's proving hard to grow pancreatic cells from any sort of stem cell. They seem to be missing compounds essential for their survival.
"It's the whole neighborhood" that may have to be recreated, he said.
Desperate patients don't always recognize those hurdles, laments Gearhart — who has tried to dissuade some heading overseas to clinics advertising stem cell "cures." Just last month, Israeli doctors reported the sad case of a 9-year-old with a fatal brain-disease whose parents carried him to Russia for injections of purported fetal stem cells. Not only did the injections not help, they apparently triggered a brain tumor discovered four years later.
"You try to give the message there of caution, caution, caution," Gearhart said.