The Science of Stem Cells

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The Science of Stem Cells

In late 1998, a group of scientists led by University of Wisconsin-Madison developmental biologist James Thomson became the first in the world to successfully isolate and culture human embryonic stem cells.

Because embryonic stem cells are the precursor cells to all other cell types in the human body, this accomplishment has set the stage for a revolution in medicine and basic biology.

The promise of stem cells lies in their ability to be cultured in the laboratory and, ultimately, directed to become specific types of cells or tissue that can be used to treat a host of cell-based diseases such as juvenile diabetes, Parkinson's and heart disease.

Stem cells arise early in development, when embryos are less than a week old, and exist there in an undifferentiated state for a very short time before going off to become other types of cells. In the course of development, they ultimately become skin cells, neurons, muscle, blood cells and every other of the 220 cell types that make up the tissues and organs in the body.

In their undifferentiated state in the laboratory, stem cells show an ability to divide indefinitely. The five cell lines established here in 1998 continue to divide, and show no evidence of a diminished ability to make more cells.

In addition to the potential for advances in health care, stem cell research also offers science its only window to the earliest stages of human development. The opportunity to study events at this stage offers insight into the unknown cellular events that cause birth defects and contribute to infertility.

Stem cell research could also yield powerful new methods for screening and testing new drugs. By creating pure populations of specific kinds of cells and exposing them to new chemical compounds, it is possible to better explore issues of drug safety and efficacy before further testing is done on animals and humans.

While stem cells hold significant clinical and technological potential, scientists are only beginning to understand their basic biology. For example, the cellular events that lead to cell specialization are not well understood and much work needs to be done before scientists are able to direct undifferentiated stem cells to become specific types of cells. There is also the potential that cultured human stem cells used in transplant medicine could face rejection by the body's immune system.

None of these technical challenges are insurmountable, but there is much work that needs to be done before stem cell therapy becomes a reality. At UW-Madison, and through the private, not-for-profit WiCell Institute, stem cell research continues on many fronts with the ultimate goal of contributing to promising new therapies and improved quality of life.

What are embryonic stem cells?
Embryonic stem cells are undifferentiated cells that are unlike any specific adult cell. However, they have the ability to form any adult cell. Because undifferentiated embryonic stem cells can proliferate indefinitely in culture, they could potentially provide an unlimited source of specific, clinically important adult cells such as bone, muscle, liver or blood cells.

Where do embryonic stem cells come from?
Human embryonic stem cells are derived from fertilized embryos less than a week old. Using 14 blastocysts obtained from donated, surplus embryos produced by in vitro fertilization, a group of UW-Madison developmental biologists led by James Thomson established five independent stem cell lines in November 1998. This was the first time human embryonic stem cells had been successfully isolated and cultured.

The cell lines were capable of prolonged, undifferentiated proliferation in culture and yet maintained the ability to develop into a variety of specific cell types, including neural, gut, muscle, bone and cartilage cells.

The embryos used in the work at UW-Madison were originally produced to treat infertility and were donated specially for this project with the informed consent of donor couples who no longer wanted the embryos for implantation.

In virtually every in vitro fertilization clinic in the world, surplus embryos are discarded if they are not donated to help other infertile couples or for research. The research protocols were reviewed and approved by a UW-Madison Institutional Review Board, a panel of scientists and medical ethicists who oversee such work.

Why are embryonic stem cells important?
Embryonic stem cells are of great interest to medicine and science because of their ability to develop into virtually any other cell made by the human body. In theory, if stem cells can be grown and their development directed in culture, it would be possible to grow cells of medical importance such as bone marrow, neural tissue or muscle.

The first potential applications of human embryonic stem cell technology may be in the area of drug discovery. The ability to grow pure populations of specific cell types offers a proving ground for chemical compounds that may have medical importance. Treating specific cell types with chemicals and measuring their response offers a short-cut to sort out chemicals that can be used to treat the diseases that involve those specific cell types. Stem cell technology, therefore, would permit the rapid screening of hundreds of thousands of chemicals that must now be tested through much more time-consuming processes.

The study of human development also benefits from embryonic stem cell research. The earliest stages of human development have been difficult or impossible to study. Human embryonic stem cells offer insights into developmental events that cannot be studied directly in humans in utero or fully understood through the use of animal models. Understanding the events that occur at the first stages of development has potential clinical significance for preventing or treating birth defects, infertility and pregnancy loss. A thorough knowledge of normal development could ultimately allow the prevention or treatment of abnormal human development. For instance, screening drugs by testing them on cultured human embryonic stem cells could help reduce the risk of drug-related birth defects.

How might embryonic stem cells be used to treat disease?
The ability to grow human tissue of all kinds opens the door to treating a range of cell-based diseases and to growing medically important tissues that can be used for transplantation purposes. For example, diseases like juvenile onset diabetes mellitus and Parkinson's disease occur because of defects in one of just a few cells types. Replacing faulty cells with healthy ones offers hope of lifelong treatment. Similarly, failing hearts and other organs, in theory, could be shored up by injecting healthy cells to replace damaged or diseased cells.

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Why not derive stem cells from adults?
There are several approaches now in human clinical trials that utilize mature stem cells (such as blood-forming cells, neuron-forming cells and cartilage-forming cells). However, because adult cells are already specialized, their potential to regenerate damaged tissue is very limited: skin cells will only become skin and cartilage cells will only become cartilage. Adults do not have stem cells in many vital organs, so when those tissues are damaged, scar tissue develops. Only embryonic stem cells, which have the capacity to become any kind of human tissue, have the potential to repair vital organs.


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