More MS news articles for July 2001

Cell Versatility: How It May Cure Diseases

07/10/2001 - Tuesday
by Earl Lane
Washington Bureau

Washington - Human embryonic stem cells, first isolated by researchers in 1998, hold great medical promise but also have been the focus from the outset of a contentious political and ethical debate.

Such cells, obtained from spare embryos slated to be discarded at fertility clinics, could be used to create custom-designed cells for use in medical treatment - insulin producing cells to cure diabetes, muscle cells for implant in diseased hearts, brain cells to treat Parkinson's and Alzheimer's diseases.

Scientists are excited about embryonic stem cells because of their versatility. Scientists have known that even adults harbor stem cells in bone marrow and elsewhere that are capable of replenishing vital tissues. Liver stem cells give rise to more liver cells, for example. Recent research suggests that even adult stem cells may be able to develop into more diverse kinds of tissue than previously thought.

But it is the embryonic stem cells that are considered to be truly remarkable, able to proliferate indefinitely once isolated and potentially to turn into any of the dozens of specialized types of cells - skin, hair, muscle, kidney - that make up the human body.

To understand what such cells are, and are not, consider first what happens when a sperm fertilizes an egg. It creates a single cell capable of forming an entire organism through many successive cycles of cell division and specialization.

In the first hours after fertilization, as the egg divides into two cells and then four, each of those early cells continues to be non-specialized and "totipotent," according to a National Institutes of Health primer on stem cells.

But after about five days, and additional cycles of division, the cells form a hollow sphere, called a blastocyst, that is ready for implant on the uterine wall. The outer layer of the sphere will go on to form the placenta and other tissues, such as the umbilical cord, needed for fetal development in the womb. The inner cluster of cells will go on to form virtually every type of cell found in the human body.

In November 1998, James Thomson and his colleagues at the University of Wisconsin at Madison reported that they were able to extract inner cells from blastocysts, grow them in a culture medium and isolate single cells that then continued dividing indefinitely while retaining the potential to grow into a wide variety of specialized cells.

At the same time, Dr. John Gearhart of Johns Hopkins University in Baltimore and his colleagues reported isolating a source of similarly adaptable stem cells from human fetal tissue.

Scientists note that embryonic stem cells, drawn from the inner mass of the blastocyst, are not the equivalent of embryos. If implanted in a womb, they will not grow into a baby because they do not have the potential to make the placenta and other specialized tissues needed for a successful pregnancy.

But opponents of embryonic stem cell research say it is unethical to use such cells for medical studies, no matter how promising, because they are obtained initially from the destruction of surplus embryos which they regard as sanctified human life.

Since 1995, Congress has banned federal funding of research in which a human embryo is destroyed or injured. Thomson's research was privately financed, and a privately financed spinoff from the University of Wisconsin Medical School has been offering embryonic stem cell lines for sale to other researchers. Such privately financed stem cell research can continue.

But experts say a federal role in funding of embryonic stem cell research would bring more investigators into the field, stimulate more open exchange of ideas and data and provide more oversight over developments. The Clinton administration proposed to finesse the funding issue by continuing to ban use of federal money to create stem cell lines derived from surplus embryos. But it proposed allowing federally funded researchers to study and use embryonic stem cell lines that had been created through private funding and then made more widely available for publicly funded research.

Opponents of using embryonic stem cells cite the promising research on the potential of stem cells derived from tissues of fully grown adults, such as those in the bone marrow that replenish blood cells throughout a person's life.

Animal research suggests such adult stem cells, previously thought to be committed to developing only certain types of specialized cells, may be more versatile. Studies in rats suggest that stem cells in the bone marrow can produce liver cells, for example. But scientists say it is by no means clear that various types of adult stem cells will ever have as much adaptability as those derived from early embryos.

As one option, the Bush administration reportedly is considering limiting federally funded researchers to using only the embryonic stem cell lines that already have been established in the lab. But scientists say the handful of cell lines already available is not enough to fully explore the potential of embryonic stem cells, particularly since studies in mice suggest there are subtle differences between embryonic stem cell lines that must be explored.

They argue that dozens of stem cell lines must be established if the research effort is to go forward.

The Debate Over Stem Cell Research President George W. Bush will soon decide whether to fund research using stem cells derived from human embryos.

All cells in the human body originate from stem cells-unspecialized master cells that renew other cells that die or become damaged.

USING STEM CELLS FORM EMBRYOS Undifferentiated stem cells from embryos are able to develop into any cell in the body. There are two possible sources: o Existing embryos: In vitro fertilization for infertility treatments creates many more embryos than needed. Those that are not implanted can be used to harvest stem cells.

Cloned embryos: Researchers working with mice have created cloned embryos using DNA from a donor mouse. Stem cells from the cloned embryo develop into other cells that won't be rejected when transplanted into the original mouse.

A blastocyst is a hollow ball of about 100 cells that forms about a week after fertilization. Stem cells are removed from blastocysts at this early stage.

Stem cells multiply in culture and then, when bathed in certain chemicals, differentiate into specific cells and tissue types.

The Debate Over Stem Cell Research o Adult stem cells, found in bone marrow and other tissues, may be less versatile than those from embryos; for example, researchers haven't been able to make stem cells found in blood develop into brain cells that could help treat Parkinson's.

SOURCES: Science, National Bioethics Advisory Commission, University of Wisconsin-Madison
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