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What Can Stem Cells
Really Do?

By Raja Mishra, Globe Staff, 8/21/2001

Source: This story ran on page C1 of the Boston Globe on 8/21/2001.
Copyright 2001 Globe Newspaper Company.

READING - Inside the Fertility Center of New England in Reading are several waist-high freezers. Inside the freezers are hundreds of pinpoint-thin straws. And in the straws are human embryos, each smaller than the period at the end of this sentence.

Some will be implanted in women. Most end up in the trash. The ongoing national debate on stem cells begins there.

''See these little gray circles - that's them,'' said lab supervisor May Fung as she held microscope-enhanced photos of the embryos, whose rough textures resemble moon rocks.

Fung goes about her task - helping impregnate women - quietly, shuffling from freezer to microscope to incubator. But the debate has been anything but quiet, especially since President Bush earlier this month allowed limited taxpayer funds to support research on embryonic stem cells. Supporters claim the new field has boundless potential for medicine. Opponents equate it with murder. Much of the public is confused about this quite new sliver of biology - and scientists have not always helped clarify the issue, mingling optimistic predictions with firm facts. What follows is a primer on stem cells.

What is a stem cell?

Every person begins as a single cell - the fertilized egg - and grows into an enormously complex machine, a unified network of billions and billions of cells. Stem cells are behind this transformation.

Within that initial cell is all the information needed to create a person. Hours after fertilization, the cell divides. Then it divides again and again. Within five days, there is a cluster of about 150 cells called the blastocyst. In the inner core of the blastocyst are embryonic stem cells.

As time passes, they will receive genetic signals to change. Some will become bone cells. Some heart cells. Others will form the cells of the brain.The body has more than 200 types of cells. The stem cells in the blastocyst are called ''pluripotent'' - they can become any one of those types. And as long as they remain stem cells, they can divide indefinitely. Once they start to specialize, they cannot.

Scientists extract the mass of stem cells from the blastocyst for research. They store them in such a way that they do not specialize. Instead, they keep dividing, producing a mass of stem cells with the same DNA, called a ''line.'' As long as the line continues to reproduce, many researchers can draw from this supply for their experiments.

But, in the process of extracting the cells, the blastocyst is destroyed.

Is a blastocyst a person?

Many believe that life begins the moment the egg and sperm fuse to form the first cell. At this point, they believe, the cell is given a soul, otherwise known as ''ensoulment.''

By this reasoning, the blastocyst is morally just like a person, endowed with the same basic human rights. To destroy the blastocyst is murder, in their view. And stem cell research, whatever benefit it may have, comes at the expense of this slaughter, they feel.

Supporters of embryonic stem cell research fall into two camps. There are those who believe that an embryo should not be considered a human life until well into a pregnancy. Some say after three months; others after six. A smaller group believes life starts at birth.

There are also stem cell researchers who believe ensoulment occurs quite early, but later than the blastocyst stage. They point out that a blastcyst still has potential to become twins. How, then, can it have a soul? They believe as soon as the stem cells start on their missions and the faint signs of a person appear, then ensoulment occurs. In this camp, many believe three weeks into a pregnancy, when the spine emerges, is the magic threshold.

How can stem cells cure disease?

Most major diseases involve the destruction of cells - Parkinson's disease, diabetes, liver disease, cancer, spinal injuries, burns, multiple sclerosis and Alzheimer's disease, to name a few.

Scientists theorize they can coax stem cells to become whatever new cells a patient needs. A Parkinson's victim can get new brain cells. A burn victim, new skin cells. And so on.

Does this really work?

We know plenty about embryonic stem cells - in mice.

In 1981, scientists first successfully removed mouse stem cells and stored them in a lab. It wasn't until 1998 that this was repeated with human cells. In mice, scientists have used the cells to cure paralysis, diabetes and brain disease. This has generated enormous hope among researchers. But mouse cures do not mean human cures.

Researchers have had limited success in coaxing human stem cells to become pancreatic cells, cardiac cells and blood cells.

How close are the answers?

In reality, we know surprisingly little about stem cells. Fundamental questions remain: What is the mechanism by which they specialize? How can we control what they become? How can we deliver them to patients with precision?

Even if stem cell research takes off in the coming years, researchers estimate it will be at least five years before the first clinical tests begin. And many of these will fail.

Can scientists use the existing stem cells?

Bush said in his televised address that only stem cell lines already in existence as of three weeks ago could be used for taxpayer-funded research. No new embryos could be destroyed for federal research.

Bush said that 60 or so stem cell lines exist around the world. But that doesn't mean researchers will have access to all 60 lines. Some researchers believe the true number is far lower. The ownership of many of the lines are shrouded in secrecy. And researchers suspect that many of the lines Bush is counting on are unusable. The Wisconsin lab that harvested the first five lines of embryonic stem cells has acknowledged that two of those lines cannot be used for research.

What happened?

To keep stem cells from specializing requires a carefully controlled lab environment, all the more difficult because scientists don't know exactly what makes these cells specialize. Sometimes the stem cells researchers cultivate spontaneously start specializing. Their ability to multiply then ends, and the line dies out.

The other problem is a common one in labs - contamination. A infectious organism can render a line scientifically useless. And sometimes lines die out for reasons unknown.

What about adult stem cells?

The blastocyst is not the only place in which stem cells are found. In fact, from conception to death, stem cells are present.

Stem cells with potential to become bone marrow cells are found in umbilical cord blood, which is usually discarded after birth. Already, these cells are used to treat leukemia victims and other severely ill patients whose immune systems are crippled by chemotherapy.

Many types of stem cells exist in adults. Embryonic stem cell opponents have seized on this, stating that embryos do not have to be destroyed to get the cells.

Scientists have identified adult stem cells in bone marrow, the brain, blood vessels, bone, skin, eyes, teeth, liver and several other tissue types. But they are very difficult to find and isolate.

Adult and embryonic stem cells differ in fundamental ways. Embryonic stem cells can multiply indefinitely, enough to potentially treat disease. Their adult counterparts proliferate less, limiting their supply.

Adult cells also have a more limited ability to specialize. Embryonic cells can become any of the 200 or so body tissues. But adult cells appear limited by their environment. For instance, adult stem cells in the blood can transform only into cell types related to blood. Scientists have had limited success in coaxing adult stem cells to transform into other types of cells, with skin stem cells appearing to have great promise. But much of the work has been done in mice.

Some have proposed that adult stem cells can be coaxed ''backward'' into embryonic stem cells. This has not been proved.

There remains much research to be done into both adult and embryonic stem cells. Most scientists are uncertain what they will find.

Does the Bush decision mean that no embryos will be destroyed?

No. Bush's decision did not outlaw any stem-cell work. He simply declared that no federal research money could go to scientists who either create or use fresh lines of embryonic stem cells.

And since the advent of test-tube fertilization in the 1980s, modern fertility science has been creating unneeded extra embryos.

On a recent morning, Fung at the Reading fertility clinic prepared for the moment of truth. A woman had come in for implantation. Earlier, seven of her embryos were frozen. Then they were exposed to her husband's semen. They were placed in an incubator that mimics the conditions inside a woman and, within days, three appeared to develop promisingly.

The team decided to implant two. This would increase the chances that one would take. But implanting all three might result in a multiple pregnancy, which the fertility center discourages.

The woman lied on the operating table as a team of embryologists brought the precious cargo to the implantation doctor. Later, the woman would throw the leftover embryos in the trash.

Until the stem cell debate erupted recently, this simple act occurred thousands of times a year, mostly unnoticed.

For more information on stem cells, visit:

Source: This story ran on page C1 of the Boston Globe on 8/21/2001.
Copyright 2001 Globe Newspaper Company.

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