Actor quadraplegic Christopher Reeves wants the Pope to read this:.....Stem cells help paralyzed mice walk
Work using human fetal cells is likely to ignite raging debate
By Charlene Laino
MSNBC
BAR HARBOR, Maine, July 24 — In a novel experiment, human stem cell transplants have allowed paralyzed lab animals to walk again — the first time such transplants have given rise to any type of recovery, scientists said Tuesday. The work used “smart” cells derived from human fetuses, which along with embryonic sources, are at the center of a controversy raging throughout the world.
IN THE latest feat to grow out of the controversial research, motor function was restored to all 80 paralyzed mice and rats given an infusion of stem cells from aborted human fetuses, reported John Gearhart, a researcher at Johns Hopkins Medical Institutions in Baltimore.
While a normal gait was not restored in the animals and many obstacles need to be overcome before human trials can even be considered, “we have now demonstrated proof of concept,” Gearhart said here at a genetics meeting at Jackson Laboratories.
Mouse stem cells have already been successfully used in a range of experiments. But a human source is needed should the work ever proceed to people, Gearhart explained, as the body tends to reject tissue from other species.
Researchers at the meeting were generally enthused about the new work’s potential, but universally stressed that the field is still in its infancy.
STEM CELL CONTROVERSY
The building blocks of all other cells in our bodies, stem cells have taken center stage in recent months. Many scientists say that transplanting such cells opens the door to growing new brain, bone, cartilage, fat and muscle tissue — in virtually unlimited amounts — to replace diseased parts of the body.
The controversy: The best source of stem cells is considered to be embryonic and fetal tissue. Not only do these cells have the potential to become any kind of cell in the body, but they also seem to have the ability to survive indefinitely. They are more flexible than adult stem cells, some researchers say.
But such stem cells, by definition, must be taken from an embryo or a fetus, usually after an abortion. And that, claim some, is taking a human life.
Stem cells: all the facts
Just what is an embryonic stem cell, anyway? To find out answers to your frequently asked questions, choose a question below.
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The U.S. government has already put on hold a plan approved by former President Bill Clinton that would provide federal funds for human embryonic and fetal stem cell research. President George W. Bush has said he will decide any day now whether to allow such funding.
Anti-abortion groups are pushing for an all-out ban on any such research. And, on Monday, Pope John Paul II told Bush he should reject practices that “devalue and violate human life.”
But Bush, who said he opposed such funding during last year’s presidential campaign, has been under mounting pressure in Congress to allow the funding. Included among those trying to persuade him of embryonic and fetal stem cells’ vast medical potential are some conservative Republicans who, like Bush, oppose abortion.
Researcher Gearhart said the federal funding is urgently needed, telling reporters that the experiments that could benefit millions carry a high price tag.
STUDY DETAILS
For the new research, Gearhart used a virus to induce a spinal cord disorder characterized by complete paralysis in 50 mice and 30 rats. While not the exact equivalent of any human disorder, “it has characteristics of the motor neuron destruction of amyotrophic lateral sclerosis [often referred to as ALS or Lou Gehrig’s disease] as well as spinal atrophy and polio,” Gearhart said.
Tests showed that by one month later, 97 percent of specialized nerve cells known as motor neurons were obliterated in the lab animals.
In an attempt to reverse the disease’s destructive progression, a small tube was placed on the tip of each animal’s spinal cord, and stem cells that were programmed to become nerve cells — but were not yet fully mature nerve cells — were infused into the cerebrospinal fluid, a cushion that lines the entire spinal cord.
The stem cells floated along the entire length of the spinal cord and migrated through the cord’s membrane and into the spinal cord, right to the site of injury — in this case, the so-called ventral horns in the hind brain, Gearhart said.
By three months after surgery, “every one of the animals was walking,” said Gearhart, stressing that their gait is not normal. Nonetheless, he said he considers their recovery remarkable.
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“Their hind limbs went from being completely flaccid and dragging to having some muscle movement,” he said. “Gradual improvement continued: They started to draw in their limbs, then they could support some weight. Eventually gait was restored, though it was twitchy. But they are ambulatory.”
While the scientists still aren’t completely sure why gait was restored, Gearhart said there is evidence of at least two mechanisms at work. First, the programmed human stem cells mature into human motor neurons that stepped in and replaced the damaged neural cells in the rats and mice, he said. In addition, he said, they secreted a substance known as a growth factor that caused the animals’ own motor neurons to regenerate.
Gearhart stressed that the technique was used in animals with paralysis due to motor neuron loss; they still had intact spinal cords. This is not the same as paralysis due to spinal cord injury, such as that suffered by actor Christopher Reeve, so this technique may not be applicable to such injuries.
The research, which was funded by Project ALS, a New York-based nonprofit organization, has been submitted to a major journal for publication.
QUESTIONS REMAIN
Gearhart has already started testing the technique on monkeys. But, he and others said, many questions remain to be answered before human tests can start.
Davor Solter of Germany, a pioneer in the field, expressed concern that the technique could cause tumors to form months, even years, down the line. Whenever one induces cell proliferation — a characteristic of cancerous cells — that is a worry, explained Johns Hopkins’ Dr. David Valle, who was not involved with the new work.
Gearhart downplayed the risk, explaining that his lab had developed “a fail-safe system” for knocking out cancerous cells “in which any cell that produces a certain end product is destroyed.” Before instituting the system, two animals in the lab developed tumors, he said. Since then, “we’ve had none.”
Solter pointed to other unanswered questions: How many stem cells are needed for a therapeutic effect? Is using your own stem cells crucial? Does it need to be done right after injury, when these animals were treated?
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Also, the animals were given immunosuppressive drugs before the transplant so they wouldn’t reject the human stem cells as foreign bodies. While Gearhart said there’s no evidence that the drugs affected the results in any way, it remains to be seen what would happen if the drugs are not given, Solter said.
Despite all the questions, the work is “very exciting,” said Valle, a co-director of the meeting. If the early work pans out, human stem cell transplantation holds the potential “to help people whom medicine up to now has failed to help.” |
