Acquiring Stem Cells for Research

In the early 1980s, scientists learned how to pull embryonic stem cells from a mouse and grow them in a laboratory. In 1998, they first reproduced human embryonic stem cells in a lab.

Photo courtesy University of Wisconsin Board of Regents Culture trays containing human embryonic stem cells are stored in heat-controlled conditions and studied by developmental biologist James Thomson's research lab at the University of Wisconsin in Madison

Where do researchers get human embryos? Embryos can either be made via reproduction -- merging sperm and egg -- or by cloning. Researchers aren't likely to create an embryo with sperm and egg, but many use fertilized embryos from fertility clinics. Sometimes, couples who are trying to have a baby create several fertilized embryos and don't implant them all. They may donate the ones that are left over to science.

Another way to create an embryo is via a technique called therapeutic cloning. This technique merges a cell (from the patient who needs the stem cell therapy) with a donor egg. The nucleus is removed from the egg and replaced with the nucleus of the patient's cell. (See How Cloning Works for a detailed look at the process.) This egg is stimulated to divide either chemically or with electricity, and the resulting embryo carries the patient's genetic material, which significantly reduces the risk that his or her body will reject the stem cells once they are implanted.

Both methods -- using existing fertilized embryos and creating new embryos specifically for research purposes -- are controversial. But before we get into the controversy, let's find out how scientists get stem cells to replicate in a laboratory setting in order to study them.