WHAT ARE STEM CELLS?
Some call them magic seeds, for their ability to replicate indefinitely and morph into any kind of tissue. Taken from human embryos only days old, stem cells are nature's blank slates, capable of developing into any of nearly 220 cell types that make up the human body. Scientists believe they will lead to cures for diseases once thought untreatable.
1 EMBRYO An egg is fertilized or cloned to form an embryo. The embryo begins to divide.
2 1 TO 5 DAYS The embryo divides again and again and takes shape as a sphere called a blastocyst
3 5 TO 7 DAYS By this time embryonic stem cells are visible and are capable of developing into any tissue in the body
4 STEM LINE The cells are removed and grown in a Petri dish. As they divided, they create a line of stem cells
5 TISSUE PRODUCTION Using various recipes of nutrients and other factors, scientists hope to turn stem cells into any of the body's more than 200 tissues, such as:
--Pancreatic islet cells Could provide a cure for diabetes
--Nerve cells Could be used to treat Alzheimer's and Parkinson's diseases and spinal-cord injuries
--Muscle cells Could repair or replace a damaged heart
FOUR WAYS TO GET EMBRYOS
The controversy begins at the source--the human embryos that must be destroyed to retrieve stem cells. Scientists can obtain these embryos in four ways, each with its own ethical challenges. The least morally problematic--using embryos left over from fertility treatments--is the only method Bush is considering supporting. Private groups are already attempting the others.
--FERTILITY CLINICS During in-vitro fertilization, clinics routinely fuse more than one egg with sperm. That way, if implanting a fertilized egg doesn't work the first time, they can try again. This practice has left thousands of unwanted embryos stored in clinic freezers. James Thomson, left, the first scientist to establish a human stem-cell line, used such embryos.
--ABORTED FETUSES John Gearhart, above right, the Johns Hopkins biologist credited, along with Thomson, with first culturing stem cells, extracted his from fetuses donated by women at a nearby abortion clinic.
--CLONING Advanced Cell Technology of Worcester, Mass., acknowledged last week that it is trying to create cloned human embryos (euphemistically referred to as "entities") as sources for stem cells. The company has considered selling its stem cells to other researchers.
--MADE TO ORDER The Jones Institute in Virginia, where the first U.S. test-tube baby was conceived, has mixed sperm and eggs expressly to create embryos as sources for stem cells.
WHY DOES FEDERAL FUNDING MATTER?
Since a lab in Virginia has already created made-to-order embryos for stem-cell research, and another in Massachusetts is cloning embryos for the same purpose, it's hard not to wonder: Is federal money really necessary? No matter what Bush decides, stem-cell research is sure to continue. But federal funding would dramatically change the scope of this research, widening the circle of scientists involved and most likely accelerating the rate at which cures are found.
IF PRESIDENT BUSH SAYS...
YES