Could stem cells be the ultimate body repair kit?

Now what if your contractor tells you not to worry, he has a new type of building material made up of generic "fix-all" building blocks that you can deposit into the crawl space under the house? These amazing blocks find their own way to damage in the house and transform into any needed replacement part right there on the spot!

For the unfortunate homeowner, this scenario remains the stuff of science fiction. But medical researchers are hot on the trail of something like these fix-all building blocks for the repair of human tissues damaged by injury or disease. They're called stem cells and recent developments in their study were named the scientific breakthrough of 1999 by Science magazine.

Stem Cells and Neuromuscular Disease

As human beings, we're far greater than the sum of our parts. Even so, many of our parts are critical for survival and modern medicine has made tremendous progress in repairing or replacing those that fail. Over the years, we've come to accept as routine the transplant of certain organs that are absolutely essential, such as the heart, liver, lungs and kidneys.

Despite this progress, neuromuscular diseases have remained notoriously intractable. A muscle disease that affects all the voluntary muscles in the body or a nerve disease that destroys the complex web of connections distributed within the brain and spinal cord elicit the same repair problems typified by foundation damage or faulty wiring in a house. Because of the mass of the tissue involved and its distributed nature, neither muscle nor nerve is transplantable on a large scale in the way that a small, self-contained organ like a kidney is.

For these reasons, therapeutic efforts in neuromuscular disease have focused primarily on ways to stop the progress of the disease, or to prevent it from starting in the first place. Unfortunately, these types of therapies haven't yet been effective enough to stop the substantial loss of muscle and nerve that occur in many neuromuscular diseases - a problem that millions of people around the world have already experienced.

What's needed is a way to regenerate tissues already lost. And now, in response to a series of landmark scientific discoveries over the last two years, even the most conservative scientists are beginning to think seriously about muscle and nerve regeneration through transplant. The trick is that instead of transplanting whole organs, they want to transplant the components to build those organs and then stimulate this to happen naturally within the body, as it does when a baby develops in the womb.

The Stem Cell Revolution

It all comes down to stem cells. Stem cells, unlike other kinds of cells that we hear about - muscle cells, nerve cells, bone cells, etc. - are like children who don't know what they want to be when they grow up. Rare stem cells that haven't ruled out any sort of future career are known as totipotent cells. They can contribute to any type of tissue. Other stem cells that have ruled out some possibilities but not others are called pluripotent stem cells.

Researchers have known about the existence of totipotent and pluripotent stem cells for a long time because they play an important role in the early development of multicellular organisms (like humans). At one time, we were each made of up of a single totipotent fertilized egg cell, which subsequently gave rise to all of the tissues in our adult body. As each new generation of cells is born, the number of careers that a cell can choose from is gradually narrowed, until most cells are designated to make a specific type of adult cell.

In 1998, two groups made headlines around the world by announcing that they'd been able to isolate, and grow in culture, early human stem cells from fetal tissue and from embryos discarded by fertility clinics. The announcement caused a stir of excitement as well as controversy. Two years later, the debate over the ethics of using fetal or embryonic stem cells still rages, and federally funded researchers are banned by Congress from conducting this research. Currently, all such research must be supported by private sources.

At almost the same time that embryonic stem cells were in the headlines, researchers were making surprising discoveries about a second, overlooked source of stem cells in the human body - adult tissues.

The surprise isn't so much that stem cells exist in the adult body (the blood, skin and lining of the gut are constantly renewed from pockets of adult stem cells), but that they exist in organs such as the brain that weren't thought to regenerate beyond early infancy, and that adult stem cells are far more versatile in their capabilities than once thought.

For instance, our red blood cells only live 120 days and are regenerated from a population of adult stem cells that are found in the spongy matter inside bones, the bone marrow. The stem cells in bone marrow also produce some of the cells of the immune system.

But in spring 1998, researchers at the Telethon Institute for Gene Therapy in Milan, Italy, published an article in Science demonstrating that transplanted bone marrow cells could help form new muscle tissue at the site of a muscle injury in mice. And, last April, researchers from a company called Osiris Therapeutics and from Johns Hopkins University in Baltimore demonstrated that bone marrow stem cells grown in the lab could also give rise to cartilage, fat and bone cells under the right circumstances.

Meanwhile, other groups demonstrated that stem cells isolated from the brains of mice can become blood cells when transplanted into the bone marrow, and that bone marrow stem cells can turn into certain types of brain cells if injected into the fluid-filled spaces, or ventricles, of the brain.

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