(CNN) -- The Food and Drug Administration has approved the first human clinical trial of embryonic stem cell therapy. The stem cells used for this study came from the 60 existing stem cell lines approved in August 2001 by the Bush administration. Before that time, federal research dollars were not allowed to be used for stem cell research.
Stem cells have the ability to turn into any organ or tissue cell in the body.
To date, only 21 of these lines have proved useful to researchers.
What are stem cells?
Embryonic stem cells have the potential to turn into any organ or tissue cell in the body.
Stem cells have this ability for a very short time. Just a few days before the embryo would implant, it starts to develop into specific cells that will turn into skin or eyes or other parts of a developing fetus.
How do scientists get stem cells?
At this point, researchers use embryos that have been created in fertility clinics by taking an egg, which is fertilized with a sperm in a petri dish. Stem cells are not removed from embryos that have been conceived naturally. The embryos used for research are not intended for making a baby, and researchers need to get consent from the parents to use their fertilized eggs for their studies.
When the embryo is 4 or 5 days old, scientists extract the stem cells and put them in a petri dish. With the removal of these stem cells -- of which there may be about 30 -- the embryo is destroyed. This is why some people oppose this type of research.
What is a "stem cell line"?
When human embryonic stem cells are placed in a petri dish, they are surrounded by a solution or "medium" that allows the cells to multiply while still having the potential to turn into any type of body cell. According to the National Institutes of Health, after six months of culturing, these original 30 cells can turn into millions of embryonic stem cells. These millions of stem cells are called a "stem cell line." Researchers will continue to monitor these cells to ensure that their properties haven't changed.
Where are these stem cell lines kept?
All of the 21 remaining federally approved stem cell lines are kept at the National Stem Cell Bank at WiCell Research Institute in Madison, Wisconsin.
The last two approved lines were deposited in this stem bank January 12. For a fee, researchers can apply for access to use stem cells for their research.
All About Stem Cell Research