The most straightforward way to find out whether a drug or environmental chemical might harm an unborn baby is to test its effect on a pregnant lab animal. In recent years, however, the thousands of chemicals in need of testing—in food, cosmetics, and medicines, for example—have driven researchers in industry and government to search for in vitro alternatives with the hope of reducing the number of animals required.
Increasingly, embryonic and induced pluripotent stem cells from humans and animals alike have been put to work in such toxicology studies. In 1997, scientists introduced the mouse embryonic stem cell test, or EST, which assesses the effects of a chemical on cell differentiation and death. Today, the EST is one of the most widely used in vitro toxicity assays. Several pharmaceutical companies, such as Pfizer and Merck, use the EST for preclinical toxicity screening, and the US Environmental Protection Agency (EPA) and ...
