Embryonic Stem Cells & Other Stem Cells Promise to Advance Treatments
While the attention of the public and ethicists has been focused on embryonic stem cells, research into other kinds of stem cells -- including the kind of adult bone-marrow stem cells Clegg received -- has been advancing and, in some cases, exploding. "I have never been in a field that is moving at this pace," says
But scientists still call embryonic cells the "gold standard" for stem cells, which is why they've been the subject of privately- and state-funded research while federal funds were restricted. It's also why researchers are excited about Obama's move to allow the government to fund research using lines of embryo-derived cells, as long as the embryos are left over from fertility treatments, not created solely for research purposes.
A maturing field
The earliest therapeutic breakthroughs are likely to arise from adult stem cells, which exist in everybody in many subtypes -- blood-producing stem cells in the bone marrow, for example, and stem cells in the brain that can become neurons and other brain cells. "In the short term -- say, the next five years -- most of the therapeutic applications from stem cells will be from adult stem cells," says
A host of ongoing projects are testing adult stem cells.
In one, researchers at the
Or, they may lead to new drugs
"The way stem cells [used as therapy] exert much of their power is to provide the chemical signal to turn on [existing but dormant] stem cells in the body," says
But adult cells can be reprogrammed into only a limited number of other cell types, which is where they fall short of more versatile embryonic stem cells. The latter are pluripotent, which means they can become pretty much any type of human tissue. But that comes with problems. "They're the teenagers of stem cells; they have great potential, but we can't always get them to do what we want them to do," says
Guiding their differentiation -- their journey to becoming a specialized cell or tissue -- with a lab-made brew of growth factors and other chemicals is a big scientific challenge, and it's not the only one. "You want to be sure you can differentiate [the stem cell] into the therapeutic cells," says
So eyes are on
It's that latter problem that makes scientists particularly excited about iPS cells, which would have the clinical potential of embryonic cells but can be created from a patient's own cells. Reprogramming an adult cell into an embryolike, more malleable state sidesteps the issue of immune rejection, not to mention the moral debate. It's also simple in concept -- adding just four genes to an adult cell can do the trick. But the virus needed to transport the genes into adult cells poses a cancer risk. In late April, scientists reported a breakthrough in mice: They induced pluripotency by inserting proteins, which don't require a virus to carry them, instead of genes, which do. In June, researchers said they'd accomplished the same thing with human cells.
Less than perfect. Some scientists, including
It will be years, if not decades, before iPS cells can be refined enough to use in patients
But even if treatments are years off, Chernoff says iPS cells have another, more immediate use: to study the progression of a disease. Researchers could take normal and malignant cells from a pancreatic cancer patient, for example, turn back the clock on both, and then reprogram the cells to form pancreatic tissue. They could then monitor the cancer-derived cells to see what, exactly, goes wrong.
Despite obstacles, scientists are cautiously optimistic that iPS, embryonic cells, or both can lead to new therapies
Type 1 diabetes and certain disorders of red blood cells are good targets, says Gasson. Replacing retinal cells damaged by macular degeneration, regenerating the immune system, and creating new cartilage in arthritis patients are, in theory, also relatively straightforward applications, adds West. If stem cells can be made to work in those simpler cases, they may be able to tackle more complex conditions, like Alzheimer's or even limb regeneration, he says. And more technical leaps may be coming; research in mice suggests it might be possible to avoid turning an adult cell's clock back entirely and instead reprogram it directly into another type of adult cell.
As for Clegg, it's too soon to tell if his will be an early success story in a stem cell treatment revolution.
So far, 13 other patients have enrolled in the same trial, and the company running it,
Meantime, doctors are monitoring Clegg. Within months after his surgery, his ejection fraction, a measurement of the percentage of blood pumped from the heart with each beat, had improved to almost 30 percent.
While shy of what's normal, that's nearly three times what it was before his procedure.
"His heart function has improved, and he's going to the gym. Can I say it's all [a direct result of] the stem cells? No," says
"It's potentially an isolated instance, or it may be the tip of the iceberg."
The same could be said for every apparent stem cell advance. With each, patients and the public are waiting, hopeful it's the latter.
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